Systematic Analysis of the Relationship among 3D Structure

Oct 5, 2017 - Graduate School of Bioresources, Mie University, 1577 Kurimamachiya-cho, Tsu 514-8507, Japan. ‡Graduate School of Pharmaceutical Scien...
0 downloads 11 Views 4MB Size
Download PDF
Article Cite This: J. Org. Chem. 2017, 82, 11447-11463

pubs.acs.org/joc

Systematic Analysis of the Relationship among 3D Structure, Bioactivity, and Membrane Permeability of PF1171F, a Cyclic Hexapeptide with Paralyzing Effects on Silkworms Yuichi Masuda,*,†,‡ Ren Tanaka,‡ A. Ganesan,§ and Takayuki Doi*,‡ †

Graduate School of Bioresources, Mie University, 1577 Kurimamachiya-cho, Tsu 514-8507, Japan Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aza-Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan § School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom ‡

S Supporting Information *

ABSTRACT: PF1171 hexapeptides, a family of cyclic hexapeptides produced by fungi, exhibit paralyzing effects on the larvae of silkworms via oral administration. To elucidate the structural features of PF1171 hexapeptides that are crucial for bioactivity, the relationship among 3D structure, bioactivity, and membrane permeability of PF1171F (the peptide with the highest bioavailability) was systematically analyzed through the synthesis of 22 analogues. The PF1171F analogues were prepared by the solid-phase synthesis of a linear precursor and subsequent solution-phase macrolactamization. Analysis by NMR spectroscopy and molecular modeling indicated that the major 3D conformations of PF1171F in various solvents resemble its X-ray crystal structure. The analogues with this conformation tend to exhibit potent paralysis against silkworms, indicating the significance of the conformation in the paralysis. The biological activity was dependent on the mode of administration, varying between hemolymph injection and oral administration. Parallel artificial membrane permeability assay (PAMPA) of the analogues revealed a correlation between membrane permeabilities and paralytic activity by hemolymph injection, indicating that the target molecule of PF1171F is present inside the cell membrane.

■

INTRODUCTION Cyclic peptides can form unique 3D structures because of the various amino acid residues involved and the potential for intramolecular interactions between these residues within macrocyclic structures. The 3D conformations are essential for specific interactions with biomolecules, which trigger bioactivity. In addition, compared to linear peptides, cyclic peptides have been reported to favor metabolic stability1,2 and cell membrane permeability.3,4 Because of these advantages, cyclic peptides have been attracting considerable attention as a source of bioactive compounds.5 The 3D structures of cyclic peptides are maintained by an intricate balance of hydrophobic and hydrophilic interactions, steric repulsions, hydrogen bonds, and other noncovalent interactions. Thus, the modification of a local structural unit in a cyclic peptide possibly affects this intricate balance, leading to the transformation of the global 3D structure. Despite the fact that the cyclic peptide is considered to be more rigid than the corresponding linear peptide, the conformational flexibility of cyclic peptides makes it difficult to understand their structure− activity relationship (SAR).6−9 Moreover, hydrogen bonds formed by amides are easily perturbed by the external environment. For example, the intramolecular hydrogen bonds formed in a hydrophobic environment, such as organic solvents and cell membranes, can be transformed into intermolecular ones in a hydrophilic environment, such as water and fluid.10,11 As the 3D structure of cyclic peptides is © 2017 American Chemical Society

affected by a number of intra- and intermolecular interactions, it is extremely difficult to design cyclic peptides with specific 3D structures. Several natural-source-derived bioactive cyclic peptides form exquisite 3D structures via the fine balance of interactions. A notable example is cyclosporin A (CSA), which is a cyclic undecapeptide clinically used as an orally bioavailable immunosuppressant.12 CSA has attracted interest as an excellent model for medium-sized bioavailable molecules because it can penetrate the cell membrane by passive diffusion despite its high molecular weight (∼1200).13 The 3D structure of CSA has been investigated both in the free state and in the ternary complex with its target proteins, namely cyclophilin and calcineurin. In the crystal structure of the CSA complex with cyclophilin and calcineurin, CSA forms a conformation in which most of the polar groups point outward, forming intermolecular hydrogen bonds with both protein partners.14 In an aqueous solution, CSA is present in multiple conformations,15,16 and the 3D structure of a CSA analogue in water is similar to the cyclophilin-bound CSA conformation.17 However, CSA in chloroform adopts a conformation in which all of its backbone N−H groups are involved in intramolecular hydrogen bonds.18,19 This conformational flexibility indicated that CSA can form intramolecular hydrogen bonds in Received: August 6, 2017 Published: October 5, 2017 11447

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

PF1171F from a mixed solvent of chloroform, diethyl ether, and n-hexane. X-ray crystallographic analysis has revealed that the four intramolecular hydrogen bonds are crucial for maintaining the 3D structure, which is related to paralytic activity (Figure 2A).41 However, it is not clear whether the 3D

hydrophobic media, which in turn facilitates membrane diffusion via the reduction in the energetic cost associated with the desolvation of the amide N−H. In recent years, an increasing number of studies regarding the relationship between 3D structure and membrane permeability of cyclic peptides have been reported.3,20−24 In particular, insightful data have been reported for naturally occurring cyclic peptides.25−28 As a notable model of bioactive cyclic peptides, we started bioorganic chemical studies of PF1171 hexapeptides, of which four (namely PF1171A, C, F, and G) have been discovered thus far in nature (Figure 1).29−35 These analogues are produced by

Figure 2. 3D structural models of PF1171F. (A) X-ray crystal structure.41 Recrystallization solvent, CHCl3/Et2O/n-hexane = 1:130:70. Yellow dotted lines indicate intramolecular hydrogen bonds. The crystallographic data (CCDC 1006825)41 can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. (B) Lowest-energy structure of the major conformer based on NMR data. NMR solvent, CDCl3.

structure is essential for affinity to target biomolecules or disposition in vivo. This study aimed to investigate the structural features of PF1171 hexapeptides that are crucial for the regulation of their conformations and activities. In particular, the effect of environments on the 3D structure of PF1171 hexapeptides was investigated by NMR. The PF1171 analogues were systematically designed and synthesized, and the relationship among chemical structure, 3D structure, bioactivity, and membrane permeability was extensively studied.

Figure 1. Chemical structures of PF1171 hexapeptides.

several types of fungi, including the Hamigera species,29−31 Acremonium species,32 unidentified ascomycete OK-128,33,34 and the marine-sponge-associated fungus Aspergillus similanensis.35 PF1171 hexapeptides contain successive anthranilic acid (Ant), pipecolinic acid (Pip), and N-methylleucine (MeLeu) residues and three variable amino acids including D-stereoisomers. PF1171A and C have been reported to suppress the secretion of apolipoprotein B in HepG2 cells and enhance the contractile force of isolated guinea pig hearts.29 PF1171 hexapeptides have been reported to induce paralysis in the larvae of the silkworm Bombyx mori by oral administration.33,34 Silkworms produce paralytic peptide (PP), which causes paralysis in silkworms, accompanied by the contraction of muscles and the morphological alteration of hemocyte subtypes.36,37 Recent studies have suggested that PP can serve as an insect cytokine that regulates innate immune responses in multiple tissues and contributes to selfdefense.38−40 As the PF1171 hexapeptides induce paralysis similar to PP, the mechanistic action is intriguing. The above-mentioned unique structure and bioactivity have motivated us to achieve total synthesis of PF1171A, C, F, and G by the combination of solid-phase peptide elongation and solution-phase macrocyclization.41 The total synthesis of PF1171 hexapeptides and their analogues have revealed that the Ala residue in PF1171A and C exhibits D-configuration41 and that similanamide, which is isolated from Aspergillus similanensis, is identical to PF1171C.42 In bioassays, the hemolymph injection of PF1171A, C, F, and G into silkworms leads to potent paralysis, whereas epi-PF1171A and epiPF1171C, bearing L-Ala instead of D-Ala, are relatively inactive.41 We have successfully prepared a single crystal of

■

RESULTS AND DISCUSSION Comparison of Silkworm Paralytic Activities by Hemolymph Injection and Oral Administration. Previously, our group has reported the paralysis of silkworms by the administration of peptides via the hemolymph injection of PF1171A, C, F, and G.41 In this study, the suitability of these compounds for oral absorption was evaluated (Figure 3, Table S1). Notably, the peptides exhibited a different order with respect to the paralytic activity between the two modes of administration. As a typical example, PF1171C, which induced potent paralysis by hemolymph injection, exhibited poor oral bioactivity. However, PF1171F showed the best oral bioavailability. As the X-ray crystal structure of PF1171F has been reported in our previous study (Figure 2A),41 it was selected as a lead for further conformational studies. NMR Analysis of 3D Structures in Various Solvents. To investigate the effect of the environment on the 3D structure of PF1171F, NMR experiments were performed in various solvents. First, the 3D structure of PF1171F in CDCl3, a common NMR solvent, was analyzed. Dihedral angle constraints were determined from J-coupling constants between vicinal protons (3JH,H) using a J-based configuration analysis (JBCA) method43 (Table S2). For distance constraints, 2D NOESY experiments were carried out, and the cross peaks were semiquantitatively translated into three distance constraint categories (strong, ≤2.5 Å; medium, ≤3.5 Å; weak, ≤5.0 Å) according to their signal intensities (Table S2). Molecular modeling was conducted on a MacroModel (version 9.9) 11448

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

based on NMR data (Tables S3 and S4). The major conformers in octanol-d17 (Figure S3A) and CD3OH (Figure S3B) resembled those in CDCl3 (Figure 2B). However, the major structure in DMSO-d6 and the minor structures in all solvents were not determined because the NMR signals were small and broad, which made analysis difficult. The amide proton chemical shift of an amino acid residue has been recognized as an indicator of strength of the intramolecular hydrogen bonds. The increase in the hydrogen bond strength leads to a downfield amide proton chemical shift.50,51 The minor broad signals were considerably upfield compared to the major sharp signals, indicating that the intramolecular hydrogen bonds formed in CDCl3 (hydrophobic and aprotic solvent) are partly disrupted by the solvent molecules of octanol-d17 (hydrophobic, protic solvent), CD3OH (hydrophilic, protic solvent), and DMSO-d6 (hydrophilic, aprotic solvent). To investigate the effect of water molecules on the 3D structure, the NMR spectrum of PF1171F was recorded in the presence of H2O. As PF1171F exhibits poor solubility in H2O, THF-d8 containing 10% H2O was used as the NMR solvent. In addition to the major sharp peaks, small broad peaks were observed (Figure 4E,F, blue arrowheads). Molecular modeling based on NMR data (Tables S5 and S6) indicated that the major structures in THF-d8 (Figure S3C) and THF-d8 containing 10% H2O (Figure S3D) are similar to those in CDCl3 (Figure 2B). Small broad peaks were more prominent in the spectrum of THF-d8 containing 10% H2O (Figure 4F) compared to those in the spectrum of 100% THF-d8 (Figure 4E). The data indicated that H2O molecules disrupt the formation of intramolecular hydrogen bonds formed in THFd8 . The above NMR analyses of PF1171F have suggested that the major conformation with the intramolecular hydrogen bonds is observed in all solvents, and it is in equilibrium with the minor conformation without some of the hydrogen bonds in hydrophilic and/or protic solvents. However, it is extremely difficult to analyze the minor conformation in detail because of the broad, weak NMR signal. The interpretation of NMR spectra of such cyclic peptides with multiple conformations is highly challenging.6 3D Structure−Activity Relationship Study. Although considerable information about the 3D structure of PF1171F was obtained by NMR analyses, the structural features that are crucial for biological activity remain unclear. This issue can be addressed by the comparison of 3D structures and activity of synthetic analogues.52 Previously, our group has reported that PF1171A, C, F, and G with intramolecular hydrogen bonds induce potent paralysis of silkworms, whereas epi-PF1171A and epi-PF1171C, bearing L-Ala instead of D-Ala, do not form the hydrogen bonds and exhibit marginal paralytic activity.41 The data led us to compare the 3D structures and bioactivity of PF1171F analogues to reveal the 3D structural features of PF1171F that are crucial for bioactivity. PF1171F analogues (1−22, Figures 5−8, left column) were designed, where a part of the structure was replaced by a variant. The analogues can be categorized into four groups: side-chain modification (Figure 5), reversal of carbon stereochemistry (Figure 6), N-methylation or demethylation of amide (Figure 7), and cyclic structure modification (Figure 8). These analogues were synthesized by the split-and-pool method using a trityl alcohol SynPhase Lantern53 based on the synthetic route to PF1171F reported previously by our group (Scheme 1).41 Briefly, acylations of amino groups with N-α-(9-fluorenylme-

Figure 3. Paralytic activities of PF1171 hexapeptides against the larvae of silkworms by hemolymph injection and oral administration. For the hemolymph injection assay, each peptide dissolved in DMSO was injected into the fourth-instar larvae, and the number of paralyzed larvae was monitored 1 h after the injection. The data for hemolymph injection have been previously reported.41 For oral administration, an artificial diet containing each peptide (100 ppm) was given to the third-instar larvae, and the number of the paralyzed silkworms was counted 3 h after the serving. Table S1 (Supporting Information) summarizes the data after 1, 3, 5, and 24 h.

program44−46 using distance geometry followed by a conformational search using 20 000-step torsional sampling based on the Monte Carlo method with 16 distances and 1 dihedral angle constraint derived from the NMR data. An OPLS-2005 force field and a generalized Born/solvent-accessible surface area (GB/SA) solvent model were applied.47 The calculation was conducted in a chloroform environment. The lowest-energy structure in CDCl3 (Figure 2B) was almost identical to the crystal structure formed in the mixed solvent of chloroform, diethyl ether, and n-hexane (Figure 2A), indicating that the geometries of NH and CO of PF1171F in CDCl3 are the same as those in the crystal structure. To verify the presence of intramolecular hydrogen bonds, variable temperature and H/D exchange NMR experiments were performed in CDCl3 (Figures S1 and S2). The temperature dependence of amide proton values (ΔδNH/ΔT) at D-Ala, Ant, D-allo-Ile, and L-Phe was relatively small ( 40%) exhibited good membrane permeability (red markers in Figure 10), whereas impermeable compounds (PAMPA permeability, Pe < 5 × 10−6 cm/s) exhibited low activity (paralysis < 40%) (green markers in Figure 10). Moreover, no compounds that were impermeable and active (Pe < 5 × 10−6 cm/s and paralysis > 40%) were observed. These data indicated that passive membrane

permeability is possibly important for paralysis by hemolymph injection. This result indicated that putative target biomolecules of the PF1171 hexapeptide are present inside the cell membrane. The analogues that maintain the 3D structure similar to the X-ray crystal structure (such as 1−5, 8, 12, 21) exhibited good permeability. However, several exceptions were observed. For example, analogue 11 (L-Phe → D-Phe) forms almost the same 3D structure as PF1171F in CDCl3 (Figure 9B−F), but hardly passed through the artificial membrane. However, 9 (L-Pip → D-Pip) and 17 (L-Phe → L-MePhe) also exhibited good membrane permeability despite the difference in the 3D structures (Figures 6D and 7F). Compound 12 (enantiomer of PF1171F) exhibited good membrane permeability, but it was inactive probably because of the chirality of the target biomolecule. Notably, 13 (D-Ala → D-MeAla), which gave broad NMR signals in CDCl3, exhibited good membrane permeability and potent paralytic activity. This indicates that 13 can induce paralysis because it can pass through the cell membrane. As 13 cannot form 3D structures similar to that in PF1171F (Figure 7B), the 3D structure when binding to the 11454

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

Scheme 1. Synthesis of the PF1171F Analogues by Solid-Phase Peptide Elongation and Solution-Phase Macrolactamization

possibly favorable for intestinal absorption. This consideration is strongly supported by the excellent membrane permeability of 21 in PAMPA. However, 1−3 (Figure 5B−D), with a strong paralytic activity by hemolymph injection, were considerably less absorbed orally compared to PF1171F despite similar conformations and smaller size. Oral absorption of the peptides can be dependent on the proteolysis because the proteases in the midgut of silkworm were reported to exhibit strong proteolytic activity.66 However, cyclic peptides with nonproteinogenic amino acid residues tend to be resistant to proteolysis.67,68 As the subtle difference of the structure apparently affects oral absorption, a more detailed study should be carried out for revealing the mechanism.

target molecule might be different from the crystal structure (Figure 2A). In the case of 13, N-methylation might enhance the membrane permeability, as has been reported by several researchers.64 Although cyclic peptides supposedly exhibit more bioavailability compared to linear ones,3,4 Kwon and Kodadek have reported that some cyclic peptides are less permeable than their linear counterparts,65 indicating that a peptide does not cross the membrane better simply because it is cyclized. Membrane permeability should be related to several factors, such as physical properties, N- and C-termini-protecting groups, and 3D structures. For the PF1171F analogues, 22 (linear analogue) did not exhibit good membrane permeability. The 1 H NMR spectrum indicated that 22 does not form intramolecular hydrogen bonds similar to PF1171F, which possibly explains that the cyclic structure helps in the formation of hydrogen bonds in PF1171F, leading to good membrane permeability. Paralysis by Oral Administration. The oral absorption of the PF1171F analogues was investigated. An artificial diet including 100 ppm of each compound was given to silkworms, and the number of paralyzed silkworms was counted (Figure 11). Most of the analogues, which were active by hemolymph injection, did not induce paralysis by oral administration. It is noteworthy that only 21 (L-Pip → L-MeAla) caused significant paralysis by oral administration. To investigate the reason for this observation, the molecular modeling of the 3D structure of 21 in CDCl3 based on NMR data was carried out (Table S9). The 3D structure of 21 was similar to that of PF1171F (Figure 9G−I). The bulky cyclic ring of Pip was replaced with the Nmethyl group, indicating that the small molecular size of 21 is

■

CONCLUSION The 3D structure of the PF1171 hexapeptides should be closely related not only to the affinity to target biomolecules but also to the disposition in vivo. Among the naturally occurring ones, the X-ray crystal structure of PF1171F was determined and the highest paralytic activity was observed for PF1171F. To elucidate the essential structural feature of PF1171F for bioactivity, the relationship among 3D structure, paralytic activity via injection and oral administration, and membrane permeability was analyzed. The 3D structures of PF1171F in various solvents were analyzed by NMR in combination with molecular mechanics calculation. The major conformations of PF1171F in CDCl3 were similar to its X-ray crystal structure with four intramolecular hydrogen bonds. Although the major conformations of PF1171F in various solvents were found to be similar to the 11455

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

Figure 9. Comparison of 3D structures of 8 (A−C), 11 (D−F), and 21 (G−I) in CDCl3. The lowest-energy structures of the major conformer based on NMR data are shown on the left (A, D, G). Superposition of the lowest-energy structure of each analogue (green) on that of PF1171F (red) is shown in the middle (B, E, H), and segmentary views of the substituted position are shown on the right (C, F, I).

direct injection and oral administration, and membrane permeability in PAMPA were investigated. Paralytic activity by hemolymph injection showed good correlation with membrane permeability, indicating that the putative target molecules are present inside the cell. The analogues with the intramolecular hydrogen bonds exhibited good membrane permeability and potent paralytic activity. However, one analogue with a different structure such as in 13 also passed through the membrane and exhibited strong paralysis. Modification such as the N-methylation of the amide might enhance the membrane permeability of the analogues. Notably, compound 21, which has the same 3D structure as PF1171F, exhibited potent paralysis by both hemolymph injection and oral administration and good membrane permeability. Overall, a specific correlation was observed among the 3D structure, bioactivity, and membrane permeability of PF1171F. However, some exceptions make it difficult to fully interpret the SAR. Hence, the analysis of the 3D structure under physiological conditions and investigation of molecular targets are currently under consideration.

Figure 10. PAMPA permeability (Pe) versus paralytic activity by hemolymph injection. Compound numbers are shown besides the markers (PF1171F is described as “F”). The markers were categorized into four groups: permeable and active (red), permeable and inactive (blue), impermeable and inactive (green), and impermeable and active (no data).

■

X-ray crystal structure, minor conformations without the intramolecular hydrogen bonds were also observed. To investigate the important structural feature for paralysis in silkworms, a structure−activity relationship study was carried out. Twenty-two analogues were efficiently synthesized by solid-phase peptide elongation and solution-phase macrocyclization. Their 3D structure in CDCl3, paralytic activity by

EXPERIMENTAL SECTION

General Techniques. All commercially available reagents were used as received. Dry THF and CH2Cl2 (Kanto Chemical Co., Inc.) were obtained by passing through activated alumina column with commercially available predried, oxygen-free formulations. DMF (SP grade > 98%) was purchased from Watanabe Chemical Industries, Ltd. The trityl alcohol SynPhase Lantern53 (surface, polystyrene; loading, 11456

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

Figure 11. Paralytic activities of the PF1171 hexapeptides against larvae of silkworms by hemolymph injection (blue bar) and oral administration (red bar). For the hemolymph injection assay, each peptide dissolved in DMSO was injected into the third-instar larvae, and the number of paralyzed larvae was monitored 1 h after the injection. For oral administration, an artificial diet containing each peptide (100 ppm) was given to the third-instar larvae, and the number of paralyzed silkworms was counted 3 h after the serving. The data for hemolymph injection have been reported previously.41 Table S1 (Supporting Information) summarizes the data after 1, 3, 5, and 24 h. 35 μmol) was purchased from Mimotopes. Anthranilic acid (Ant), (R)-(−)-2-aminobutyric acid (D-Aba), D-valine (D-Val), and 3-amino2-naphthoic acid (Ana) were purchased from Wako Pure Chemical Industries. L-Pipecolinic acid (L-Pip), D-pipecolinic acid (D-Pip), 3aminobenzoic acid (3-Abz), and N-methylanthranilic acid were purchased from Tokyo Chemical Industry Co., Ltd. 4-Aminobenzoic acid (4-Abz) was purchased from Nacalai Tesque, Inc. D-alloIsoleucine, L-allo-isoleucine, and N-α-(9-fluorenylmethoxycarbonyl) (Fmoc)-protected amino acids (Fmoc-D-Ala-OH, Fmoc-L-Ala-OH, Fmoc-L-Leu-OH, Fmoc-L-Phe-OH, Fmoc-β-Ala-OH, Fmcoc-D-PheOH, Fmoc-D-Leu-OH, Fmoc-L-MeAla-OH, Fmoc-L-MePhe-OH, Fmoc-L-Pro-OH) were purchased from Watanabe Chemical Industries, Ltd. All reactions in solution-phase were monitored by thin-layer chromatography carried out on 0.2 mm E. Merck silica gel plates (60F-254) with UV light and visualized with a ninhydrin solution. Silica gel 60N (Kanto Chemical Co., Inc. 40−100 μm) was used for column chromatography. 1 H NMR spectra and 13C NMR spectra were recorded on a JEOL JNM-AL400 (400 MHz for 1H) or a JEOL ECA-600 (600 MHz for 1 H) spectrometer in the indicated solvent. Chemical shifts (δ) for 1H NMR spectra are referenced to signals for internal tetramethylsilane (0 ppm) and residual nondeuterated solvents (chloroform = 7.26 ppm; methanol-d4 = 3.30 ppm; dimethyl sulfoxide (DMSO)-d6 = 2.49 ppm; THF-d8 = 1.72 ppm; OH of octanol-d17 = 5.17 ppm). Chemical shifts (δ) for 13C NMR spectra are referenced to signals for residual deuterated solvents (chloroform-d = 77.0 ppm, methanol-d4 = 49.0 ppm; DMSO-d6 = 39.5 ppm; THF-d8 = 25.3 ppm; C1 of octanol-d17 = 62.2 ppm). Multiplicities are reported by the following abbreviations: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), dd (double doublet), dt (double triplet), ddd (double double doublet), ddt (double double triplet), dddd (double double double doublet), brs (broad singlet), brd (broad doublet). Coupling constants (J) are represented in hertz (Hz). Mass spectra and high-resolution mass spectra were measured on JEOL JMS-DX303 (for EI), JEOL MS-AX500 (for FAB), and ThermoScientific Exactive Plus Orbitrap mass spectrometers (for ESI). IR spectra were recorded on a JASCO FTIR-4100. Only the strongest and/or structurally important absorptions are reported as the IR data afforded in wavenumbers (cm−1). Optical rotations were measured on a JASCO P-1010 polarimeter at 589 nm. Melting points were measured on a RFS-10 melting point apparatus (Round Science Inc.) and are uncorrected. Analysis of the synthetic peptides was performed by reversed-phase high-performance liquid chromatography (RP-HPLC) on a Waters LC/MS system consisting of a Waters 600 HPLC System equipped with a Waters 2996 Photodiode array detector and a Waters Micromass ZQ 2000 unit. RP-HPLC conditions were as follows:

column, X-Bridge ODS-3.5 μm, 4.6 mm × 75 mm; flow rate, 1.1 mL/ min; elution method, solvent A/solvent B = 90:10 to 5:95 linear gradient (0.0−4.0 min), solvent A/solvent B = 5:95 isocratic (4.0− 11.0 min) (solvent A, 0.1% HCOOH/H2O; solvent B, 0.1% HCOOH/MeOH). The purity was determined with peak area at UV 214 nm. Preparative RP-HPLC was carried out on a Waters 1525EF HPLC system equipped with a Waters 2489 UV/Visible detector (monitoring at 214 and 254 nm). General Procedure for Molecular Modeling Based on NMR Data. Molecular modeling of PF1171F based on NMR data was performed in the same manner as previously reported.7,8 NMR measurements for 3D structural analysis were conducted with a NMR spectrometer (600 MHz for 1H) at 298 K using about 10 mg of each sample in 0.7 mL of solvent. 3JH,H values were determined by 1D 1H spectra and 1H−1H J-resolved 2D NMR spectra. According to a Jbased configuration analysis (JBCA) method,43 3JH,H coupling constants for clearly anti-oriented vicinal protons (3JH,H ≥ 10 Hz) were interpreted as dihedral angle constraints (Tables S2−S9). To obtain information regarding 1H−1H internuclear distances, NOESY experiments (standard pulse program ‘‘noesy_pfg_zz’’ in Delta NMR software of JEOL) were performed at a mixing time of 500 ms. NOESY cross-peak intensities were roughly determined by their peak area in 1D slices of the 2D spectra. NOE cross-peak intensities were classified as “strong” (upper distance constraint ≤2.5 Å), “medium” (≤3.5 Å), and “weak” (≤5.0 Å) (Tables S2−S9). The cross peaks between the geminal protons of Phe-CβH2 were used as internal standards for calibration. To address the possibility of conformational averaging, intensities were classified conservatively and only upper distance limits were included in the calculations to allow the largest possible number of conformers to fit the experimental data. Molecular modeling was performed on the MacroModel (version 9.9) program44−46 by the distance geometry method. We utilized an OPLS-2005 force field and a generalized Born/solvent-accessible surface area (GB/SA) solvent model.47 The calculating environments were as follows: chloroform for CDCl3, CD3OH containing 5% CDCl3, THF-d8, and THF-d8 containing 10% H2O; octanol for octanol-d17. To find 3D structures that were in agreement with the experimental data (J-coupling and NOEs, summarized in Tables S2− S9) and also had low energies in a given force field, we selected a protocol that comprised two steps. First, a conformational search was performed using Monte Carlo-based torsional sampling with 1H−1H distance constraints (force constant, 10 kJ mol−1 Å−2) and antioriented dihedral angle constraints (1H−C−C−1H angle, 180° ± 30°) at 20 000 iterations with 500 times of energy minimization. Then, 5000 times of energy minimization was conducted on each found structure without constraints. The lowest-energy structures (Figures 2, 9, and S3) along with top-10 stable structures (Figure S5) were shown. 11457

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

argon atmosphere. After being stirred at room temperature for 3 h, the reaction mixture was poured into saturated aqueous NaHCO3 and the aqueous layer was extracted with EtOAc. The organic layer was washed with brine, dried over MgSO4, and filtered. The filtrate was concentrated in vacuo, and the resulting residue was passed through a short pad silica gel and further purified by RP-HPLC (column, YMCPack R&D ODS-A 20 mm × 150 mm; flow rate, 12.0 mL/min; elution method, H2O/MeOH = 25:75 to 10:90 linear gradient (0.0−15.0 min)). 1 (L-MeLeu → L-MeAla): yield 50% (27.0 mg, 41.7 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.50 (1H, s), 8.30 (2H, d, J = 8.3 Hz), 7.57 (1H, d, J = 9.8 Hz), 7.47 (1H, t, J = 7.8 Hz), 7.39 (3H, d, J = 7.8 Hz), 7.31− 7.11 (5H, m), 4.77−4.62 (2H, m), 4.43 (1H, dd, J = 7.3, 3.2 Hz), 4.15 (1H, dd, J = 13.8, 3.3 Hz), 3.75 (1H, t, J = 7.0 Hz), 3.54 (1H, q, J = 6.8 Hz), 3.38 (1H, d, J = 14.1, 5.1 Hz), 3.27 (1H, dd, J = 14.4, 9.8 Hz), 3.22 (3H, s), 3.19 (1H, m), 2.42 (1H, m), 2.16 (3H, m), 1.83 (1H, m), 1.62 (3H, d, J = 6.8 Hz), 1.59−1.50 (1H, m), 1.42−1.28 (3H, m), 1.25 (3H, d, J = 7.3 Hz), 0.94−0.87 (6H, m); 13C NMR (100 MHz, CDCl3) δ 174.3, 173.5, 170.8, 170.5, 169.0, 168.7, 138.3, 137.0, 131.7, 129.4, 128.3, 127.1, 126.3, 123.9, 123.3, 122.7, 62.2, 61.4, 57.3, 54.6, 52.7, 47.6, 36.8, 36.3, 33.8, 27.7, 27.5, 26.8, 24.5, 18.3, 13.9, 13.0, 11.7; IR (neat) 3339, 3961, 2936, 1684, 1641, 1618, 1594, 1521, 1507, 1450, 1432, 1294, 1252, 754, 702, 667 cm−1; [α]24 D +15.3 (c 1.30, CHCl3); HRMS (ESI/IT) calcd for C35H46N6O6Na [M + Na]+ 669.3371, found 669.3354. 2 (D-allo-Ile → D-Ala): yield 26% (15.0 mg, 23.2 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.28 (1H, s), 8.26 (1H, d, J = 8.2 Hz), 8.17 (1H, d, J = 8.0 Hz), 7.65 (1H, d, J = 9.9 Hz), 7.47 (1H, t, J = 7.8 Hz), 7.36 (1H, d, J = 7.0 Hz), 7.28 (2H, m), 7.22−7.12 (4H, m), 4.70 (1H, m), 4.61 (1H, m), 4.48 (1H, m), 4.13 (1H, d, J = 11.6 Hz), 3.75 (1H, d, J = 9.9 Hz), 3.52 (1H, q, J = 4.5 Hz), 3.34 (1H, d, J = 14.1, 5.4 Hz), 3.28− 3.25 (1H, m), 3.23 (3H, s), 3.17 (1H, m), 2.34−2.18 (2H, m), 2.18− 2.07 (2H, m), 2.07−1.94 (1H, m), 1.75−1.64 (2H, m), 1.64−1.55 (2H, m), 1.52 (3H, d, J = 7.2 Hz), 1.37−1.26 (1H, m), 1.24 (3H, d, J = 7.2 Hz), 1.01 (6H, t, J = 6.2 Hz); 13C NMR (100 MHz, CDCl3) δ 174.0, 172.5, 171.0, 170.1, 169.0, 168.9, 138.1, 136.9, 131.6, 129.6, 128.3, 126.9, 126.4, 124.1, 123.4, 123.2, 65.3, 61.4, 54.7, 52.5, 49.8, 47.6, 37.9, 34.2, 27.9, 27.4, 25.6, 24.4, 23.3, 22.1, 18.2, 18.0; IR (neat) 3340, 3009, 2956, 2937, 2870, 1683, 1645, 1619, 1595, 1538, 1520, 1450, 1435, 1411, 1330, 1291, 1267, 1218, 753, 701, 667 cm−1; [α]27 D −9.80 (c 0.700, CHCl3); HRMS (ESI/IT) calcd for C35H46N6O6Na + [M + Na] 669.3371, found 669.3356. 3 (L-Phe → L-Ala): yield 19% (8.4 mg, 13.7 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.48 (1H, s), 8.33 (1H, d, J = 8.5 Hz), 8.06 (1H, d, J = 8.0 Hz), 7.51−7.44 (2H, m), 7.20 (1H, dd, J = 7.7, 1.4 Hz), 7.13 (1H, td, J = 7.5, 1.0 Hz), 4.83 (1H, m), 4.64 (1H, m), 4.45 (1H, dd, J = 7.5, 3.1 Hz), 4.14 (1H, dd, J = 13.5, 3.6 Hz), 3.70 (1H, dd, J = 11.5, 2.3 Hz), 3.48 (1H, q, J = 4.5 Hz), 3.20 (3H, s), 3.17 (1H, m), 2.46−2.38 (1H, m), 2.28−2.21 (1H, m), 2.14−1.97 (4H, m), 1.91 (1H, m), 1.74−1.54 (3H, m), 1.51 (3H, d, J = 7.0 Hz), 1.39 (2H, m), 1.29 (3H, d, J = 7.5 Hz), 1.00−0.90 (12H, m); 13C NMR (100 MHz, CDCl3) δ 174.1, 174.0, 171.0, 170.2, 169.1, 168.9, 137.2, 131.7, 127.1, 123.8, 123.3, 122.5, 65.1, 61.5, 57.3, 52.6, 48.3, 47.7, 37.91, 37.86, 36.5, 28.0, 27.4, 26.8, 25.6, 24.5, 23.2, 22.1, 18.4, 13.89, 13.85, 11.8; IR (neat) 3337, 2959, 2936, 1684, 1640, 1637, 1618, 1594, 1539, 1521, 1507, 1450, 1435, 1293, 755 cm−1; [α]24 D +14.5 (c 0.395, CHCl3); HRMS (ESI/IT) calcd for C32H48N6O6Na [M + Na]+ 635.3528, found 635.3511. 4 (D-Ala → D-Val): yield 23% (12.1 mg, 16.9 μmol) over 13 steps from Fmoc-D-Val-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.50 (1H, s), 8.26 (1H, d, J = 8.2 Hz), 8.13 (1H, d, J = 8.0 Hz), 7.60 (1H, d, J = 10.1 Hz), 7.50−7.42 (2H, m), 7.38 (2H, d, J = 7.0 Hz), 7.27 (1H, t, J = 7.4 Hz), 7.22−7.17 (2H, m), 7.12 (1H, td, J = 7.5 Hz, 1.1 Hz), 4.71 (1H, dd, J = 10.3, 3.0 Hz), 4.67−4.61 (1H, m), 4.44 (1H, dd, J = 7.5, 3.1 Hz), 4.14 (1H, dd, J = 13.3, 3.9 Hz), 3.57 (1H, q, J = 4.6 Hz), 3.36 (1H, dd, J = 13.4, 2.5 Hz), 3.28−3.24 (1H, m), 3.23 (3H, s), 3.17 (1H, m), 2.63−2.55 (1H, m), 2.49−2.39 (1H,

Atomic coordinates and calculated potential energies of the lowestenergy structures were summarized in Tables S10−S17. Syntheses of PF1171F Analogues 1−23. General Procedure for Loading First Fmoc Amino Acid to the Trityl Alcohol Lantern. A trityl alcohol SynPhase Lantern (D-series, 35 μmol/unit) was treated with a solution of acetyl chloride in CH2Cl2 (1:10, v/v) at room temperature. After the Lantern was shaken at the same temperature for 4 h, the mixture was filtered. The Lantern was rinsed with CH2Cl2 and washed five times each with CH2Cl2 to afford the trityl chloride Lantern. The resulting Lantern was immediately used for the immobilization of the Fmoc amino acid. The trityl chloride Lantern was treated with a solution of Fmoc amino acid (0.100 M) and DIEA (0.200 M) in CH2Cl2 (1.00 mL/Lantern) at room temperature, and then the mixture was shaken at the same temperature. After being shaken for 12 h, the reaction mixture was filtered. The resulting Lantern was rinsed with CH2Cl2 and then washed with CH2Cl2 (3 min × 5) and Et2O (3 min × 1). The washed Lantern was dried in vacuo to afford the polymer-supported amino acid. The immobilization yields were found to be 85% (Fmoc-D-Ala), 93% (Fmoc-D-Val), 85% (Fmoc-D-Leu), 91% (Fmoc-D-MeAla), and 85% (Fmoc-L-Ala) by gravimetric analysis after cleavage with 30% HFIP/CH2Cl2 (room temperature, 1 h) from the polymer support. General Procedure for Deprotection of the Fmoc Group. The N-Fmoc-protected peptide-supported Lantern was treated with a solution of 20% piperidine in DMF at room temperature. After being shaken for 1 h, the reaction mixture was filtered and the Lantern was washed with DMF (3 min × 5). The washed Lantern was immediately used for the next acylation. Acylation with Second−Sixth Fmoc Amino Acid on the Polymer Support. Acylation was performed by the following conditions A−C according to Table S18. General Procedure for Condition A. To a suspension of Lantern, Fmoc amino acids (0.100 M), and HOBt (0.150 M) in DMF (1.00 mL/lantern) was added DIC (0.100 M), and the mixture was shaken at room temperature. After being shaken for 12−20 h, the reaction mixture was filtered and the Lantern was washed with DMF (3 min × 3), THF/H2O (3:1) (3 min × 3), MeOH (3 min × 2), and CH2Cl2 (3 min × 2). General Procedure for Condition B. To a suspension of Lantern, Fmoc amino acid (0.100 M), and DIEA (0.200 M) in DMF (1.00 mL/Lantern) was added PyBroP (0.100 M) at room temperature, and the flask was purged with argon. After being shaken at the same temperature for 12 h, the reaction mixture was filtered and the Lantern was washed with DMF (3 min × 3), THF/H2O (3:1) (3 min × 3), MeOH (3 min × 2), and CH2Cl2 (3 min × 2). General Procedure for Condition C. The Lantern was rinsed with THF (3 min × 2) and immediately used for the next reaction. To a solution of Fmoc amino acid (0.100 M) and triphosgene (0.033 M) in THF (1.00 mL/Lantern) was added 2,4,6-collidine (0.250 M) to give a white suspension. After 1 min, the suspension was added to the Lantern, and the mixture was shaken at room temperature. After being shaken for 12 h, the reaction mixture was filtered and the Lantern was washed with DMF (3 min × 3), THF/H2O (3:1) (3 min × 3), MeOH (3 min × 2), and CH2Cl2 (3 min × 2). General Procedure for the Final Deprotection of the Fmoc Group and Cleavage from Lantern. The N-Fmoc-protected hexapeptide-supported Lantern was treated with a solution of 20% piperidine in DMF at room temperature. After being shaken for 1 h, the reaction mixture was filtered and the Lantern was washed with DMF (3 min × 5) and CH2Cl2 (3 min × 2). The washed Lantern was dried in vacuo. The dried Lantern was treated with 30% HFIP/CH2Cl2 (1.00 mL/Lantern) at room temperature. After being shaken for 1 h, the reaction mixture was filtered and the Lantern was washed with CH2Cl2 (3 min × 3). The combined filtrate was concentrated in vacuo, and the crude cyclization precursor was used for the next reaction after being passed through a short pad of silica gel (eluent, 10% MeOH/ CHCl3). General Procedure for Macrolactamization. To a solution of crude cyclization precursor (1.0 equiv) in dry CH2Cl2 (1.0 mM) was added DIEA (6.0 equiv) and then HATU (3.0 equiv) at 0 °C under an 11458

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

(c 0.600, CHCl3); HRMS (ESI/IT) calcd for C38H52N6O6Na [M + Na]+ 711.3841, found 711.3824. 8 (L-MeLeu → D-MeLeu): yield 17% (9.8 mg, 14.2 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.34 (1H, s), 8.24 (1H, d, J = 8.3 Hz), 7.80 (1H, d, J = 8.0 Hz), 7.72 (1H, d, J = 9.5 Hz), 7.47 (1H, t, J = 7.2 Hz), 7.37 (2H, d, J = 7.3 Hz), 7.28 (2H, t, J = 7.4 Hz), 7.22−7.11 (4H, m), 4.88 (1H, dd, J = 11.6, 3.8 Hz), 4.67 (2H, m), 4.50 (1H, dd, J = 7.9, 3.0 Hz), 4.15 (1H, d, J = 12.7 Hz), 3.88 (1H, dd, J = 11.0, 3.2 Hz), 3.44 (1H, dd, J = 14.4, 5.9 Hz), 3.24 (1H, dd, J = 14.1, 9.5 Hz), 3.00 (3H, s), 2.41 (1H, m), 2.26−1.98 (4H, m), 1.72 (1H, m), 1.60 (3H, m), 1.39−1.22 (4H, m), 1.19 (3H, d, J = 7.1 Hz), 1.02 (3H, d, J = 6.6 Hz), 0.99 (3H, d, J = 6.3 Hz), 0.89 (6H, m); IR (neat) 3330, 3009, 2959, 2936, 2873, 1683, 1640, 1618, 1594, 1515, 1450, 1436, 1401, 1294, 1257, 755, 701, 668 cm−1; [α]26 D +74.5 (c 0.460, CHCl3); HRMS (ESI/ IT) calcd for C38H52N6O6Na [M + Na]+ 711.3841, found 711.3822. 9 (L-Pip → D-Pip): yield 24% (12.4 mg, 18.0 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 8.90 (1H, s), 7.88 (1H, d, J = 7.6 Hz), 7.38 (1H, t, J = 7.8 Hz), 7.34 (1H, d, J = 7.6 Hz), 7.30−7.17 (6H, m), 7.17−7.04 (2H, m), 6.87 (1H, d, J = 8.0 Hz), 5.36 (1H, t, J = 7.7 Hz), 4.84 (1H, q, J = 7.6 Hz), 4.64 (1H, m), 4.53 (1H, dd, J = 9.4, 3.5 Hz), 4.42 (1H, m), 3.68 (2H, m), 3.29 (1H, m), 3.10 (1H, s), 3.05 (2H, d, J = 6.1 Hz), 2.27 (1H, m), 1.94 (2H, m), 1.85 (1H, m), 1.75 (4H, m), 1.64 (3H, m), 1.46 (1H, m), 1.26 (1H, m), 0.98 (3H, d, J = 6.6 Hz), 0.91 (6H, m), 0.80 (3H, d, J = 6.8 Hz), 0.73 (3H, d, J = 5.9 Hz); 13C NMR (100 MHz, CDCl3) δ 173.5, 173.2, 171.3, 170.8, 169.6, 136.4, 135.7, 130.8, 129.1, 128.6, 127.6, 126.9, 125.0, 124.3, 124.2, 55.8, 55.4, 54.1, 53.8, 49.1, 46.0, 37.9, 35.0, 34.4, 30.6, 26.1, 25.4, 24.9, 23.3, 23.0, 21.5, 19.4, 17.3, 14.4, 11.7; IR (neat) 3360, 3012, 2959, 2935, 2873, 1689, 1653, 1623, 1592, 1507, 1456, 1429, 1404, 1387, 1282, 1256, 1216, 754, 700, 667 cm−1; [α]25 D +47.3 (c 0.580, CHCl3); HRMS (ESI/IT) calcd for C38H52N6O6Na [M + Na]+ 711.3841, found 711.3823. 10 (D-allo-Ile → L-allo-Ile): yield 34% (13.9 mg, 20.2 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 8.04 (1H, s), 7.66 (3H, m), 7.41 (1H, t, J = 7.8 Hz), 7.32 (4H, m), 7.25−7.12 (3H, m), 6.72 (1H, m), 4.69 (1H, t, J = 8.0 Hz), 4.44 (3H, m), 3.62 (1H, m), 3.47 (1H, m), 3.34 (3H, s), 3.20 (1H, dd, J = 14.0, 4.3 Hz), 3.04 (2H, m), 2.29 (1H, m), 2.15 (1H, m), 1.97 (1H, m), 1.88 (2H, m), 1.76 (4H, m), 1.59 (4H, m), 1.50 (3H, m), 1.28 (1H, d, J = 7.2 Hz), 1.20 (3H, d, J = 7.1 Hz), 1.00 (3H, d, J = 6.6 Hz), 0.96 (3H, d, J = 6.6 Hz), 0.90 (3H, t, J = 7.3 Hz), 0.74 (3H, d, J = 6.6 Hz); 13C NMR (100 MHz, CDCl3) δ 173.8, 172.2, 171.6, 171.5, 171.4, 171.2, 136.3, 134.2, 131.5, 134.2, 131.5, 130.5, 130.3, 129.5, 129.1, 129.0, 128.8, 127.5, 127.1, 126.2, 125.6, 66.0, 58.4, 57.9, 57.1, 54.2, 48.1, 45.0, 40.5, 37.9, 35.0, 26.8, 25.8, 25.1, 23.6, 22.9, 21.4, 19.7, 16.2, 15.4, 14.7, 11.5, 11.3; IR (neat) 3319, 2959, 2935, 2871, 1684, 1676, 1636, 1629, 1522, 1498, 1455, 1291, 754, 700 cm−1; [α]25 D +39.2 (c 0.660, CHCl3); HRMS (ESI/IT) calcd for C38H52N6O6Na [M + Na]+ 711.3841, found 711.3813. 11 (L-Phe → D-Phe): yield 20% (8.2 mg, 11.9 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.54 (1H, s), 8.65 (1H, d, J = 7.2 Hz), 8.35 (1H, d, J = 8.5 Hz), 8.28 (1H, d, J = 6.8 Hz), 7.59 (1H, d, J = 9.7 Hz), 7.48 (1H, m), 7.29 (2H, m), 7.24−7.16 (4H, m), 7.12 (1H, m), 4.82 (1H, m), 4.41 (1H, dd, J = 7.4, 3.3 Hz), 4.10 (1H, m), 3.99 (1H, q, J = 7.7 Hz), 3.68 (1H, m), 3.61 (1H, dd, J = 14.0, 8.4 Hz), 3.51 (1H, m), 3.45 (1H, dd, J = 8.7, 5.1 Hz), 3.18 (3H, s), 3.13 (1H, m), 2.44 (1H, m), 2.20 (1H, m), 2.09−1.95 (3H, m), 1.80 (1H, m), 2.15 (1H, m), 1.65 (2H, m), 1.88 (2H, m), 1.50 (4H, m), 1.29 (3H, d, J = 7.2 Hz), 1.25 (1H, m), 1.01−0.93 (12H, m); 13C NMR (100 MHz, CDCl3) δ 175.2, 174.2, 170.9, 170.3, 169.1, 168.8, 137.2, 137.1, 131.7, 128.9, 128.5, 127.1, 126.8, 123.6, 123.3, 122.6, 64.9, 62.2, 61.4, 57.1, 52.7, 48.0, 38.0, 37.8, 36.6, 36.2, 27.5, 27.4, 27.1, 25.6, 24.4, 23.2, 22.1, 17.9, 14.2, 11.9; IR (neat) 3339, 3303, 2959, 2934, 1684, 1641, 1618, 1594, 1521, 1507, 1481, 1450, 1433, 1292, 755, 699, 665 cm−1; [α]25 D +45.2 (c 0.380, CHCl3); HRMS (ESI/IT) calcd for C38H52N6O6 Na [M + Na]+ 711.3841, found 711.3825. 12 (enantiomer of PF1171F): yield 32% (13.7 mg, 19.9 μmol) over 13 steps from Fmoc-L-Ala-Lantern; a white amorphous solid; 1H NMR

m), 2.34−2.25 (1H, m), 2.21−2.01 (3H, m), 1.76−1.53 (4H, m), 1.42−1.25 (3H, m), 1.02 (6H, t, J = 6.6 Hz), 0.94−0.89 (6H, m), 0.77 (3H, d, J = 6.8 Hz), 0.51 (3H, d, J = 7.0 Hz); 13C NMR (100 MHz, CDCl3) δ 173.4, 173.1, 170.7, 170.2, 170.0, 169.0, 138.2, 137.1, 131.8, 129.4, 128.3, 127.0, 126.4, 123.8, 123.4, 122.2, 65.3, 61.5, 57.2, 56.4, 54.5, 52.4, 38.1, 38.0, 36.1, 33.9, 28.6, 27.8, 27.5, 26.8, 25.6, 24.5, 23.4, 22.1, 19.3, 16.2, 14.1, 11.7; IR (neat) 3339, 2960, 2933, 1684, 1641, 1618, 1595, 1521, 1507, 1450, 1436, 1433, 1297, 754, 665 cm−1; [α]25 D +9.60 (c 0.575, CHCl3); HRMS (ESI/IT) calcd for C40H56N6O6Na [M + Na]+ 739.4154, found 739.4132. 5 (D-Ala → D-Leu): yield 33% (18.6 mg, 25.5 μmol) over 13 steps from Fmoc-D-Leu-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.44 (1H, s), 8.29 (1H, d, J = 8.5 Hz), 8.20 (1H, d, J = 7.8 Hz), 7.57 (1H, d, J = 9.8 Hz), 7.47 (1H, t, J = 7.8 Hz), 7.38 (3H, m), 7.27 (2H, t, J = 7.6 Hz), 7.19 (2H, m), 7.14 (1H, dd, J = 14.4, 6.8 Hz), 4.66 (2H, m), 4.45 (1H, dd, J = 7.6, 3.2 Hz), 4.15 (1H, m), 3.75 (1H, t, J = 7.0 Hz), 3.75 (1H, d, J = 9.9 Hz), 3.53 (1H, dd, J = 9.0, 4.4 Hz), 3.37 (1H, dd, J = 14.3, 5.0 Hz), 3.27 (1H, dd, J = 14.4, 9.8 Hz), 3.22 (3H, s), 3.19 (1H, m), 2.42 (1H, m), 2.27 (1H, m), 2.18−2.04 (4H, m), 1.84 (1H, m), 1.75−1.62 (3H, m), 1.62 (2H, d, m), 1.44 (1H, m), 1.43−1.25 (5H, m), 1.01 (6H, t, J = 6.3 Hz), 0.91 (6H, t, J = 7.0 Hz), 0.75 (3H, d, J = 6.6 Hz), 0.67 (6H, d, J = 76.8 Hz); 13C NMR (100 MHz, CDCl3) δ 174.2, 173.4, 170.8, 170.2, 169.2, 169.0, 138.2, 137.0, 131.7, 129.4, 128.2, 127.0, 126.4, 123.8, 123.4, 122.6, 65.5, 61.5, 57.2, 54.6, 52.5, 50.8, 40.3, 38.0, 37.8, 36.3, 33.8, 28.0, 27.4, 26.8, 25.6, 24.8, 24.4, 23.41, 23.38, 22.1, 21.5, 14.0, 11.7; IR (neat) 3338, 3012, 2958, 2935, 2871, 1685, 1642, 1618, 1594, 1538, 1516, 1450, 1434, 1292, 1267, 755, 701, 667 cm−1; [α]26 D +22.3 (c 0.900, CHCl3); HRMS (ESI/IT) calcd for C41H58N6O6Na [M + Na]+ 753.4310, found 753.4288. 6 (Ant → Ana): yield 35% (18.6 mg, 25.5 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.46 (1H, s), 8.77 (1H, s), 8.29 (1H, d, J = 8.2 Hz), 7.86 (1H, d, J = 8.2 Hz), 7.77 (1H, d, J = 8.0 Hz), 7.68 (2H, t, J = 4.8 Hz), 7.56 (1H, m), 7.48 (1H, m), 7.40 (3H, m), 7.29 (2H, d, J = 7.3 Hz), 7.19 (1H, m), 4.69 (2H, m), 4.53 (1H, dd, J = 7.7, 3.1 Hz), 4.28 (1H, m), 3.81 (1H, m), 3.55 (1H, d, J = 9.0, 4.6 Hz), 3.40 (1H, dd, J = 14.4, 5.2 Hz), 3.32 (4H, m), 3.27 (1H, m), 2.49 (1H, m), 2.31 (1H, m), 2.24−2.11 (3H, m), 2.06 (1H, m), 1.72 (2H, m), 1.58 (2H, m), 1.38 (2H, m), 1.30 (1H, m), 1.21 (3H, d, J = 7.5 Hz), 1.03 (6H, t, J = 6.2 Hz), 0.94 (6H, m); 13C NMR (100 MHz, CDCl3) δ 174.4, 173.5, 170.8, 170.3, 170.0, 168.8, 138.2, 134.6, 132.5, 129.5, 128.7, 128.4, 128.2, 128.0, 127.6, 127.3, 126.3, 122.9, 121.4, 65.4, 61.6, 57.2, 54.6, 53.1, 47.7, 38.0, 37.8, 36.4, 33.8, 28.1, 27.4, 26.8, 25.6, 24.5, 23.4, 22.1, 18.2, 14.0, 11.7; IR (neat) 3341, 3011, 2959, 2934, 2872, 1685, 1640, 1615, 1591, 1517, 1482, 1452, 1385, 1361, 1335, 751, 666 cm−1; [α]26 D −20.0 (c 0.800, CHCl3); HRMS (ESI/IT) calcd for C42H54N6O6Na [M + Na]+ 761.3997, found 761.3975. 7 (D-Ala → L-Ala): yield 29% (12.5 mg, 18.2 μmol) over 13 steps from Fmoc-L-Ala-Lantern; a white amorphous solid; 1H NMR (600 MHz, CDCl3) δ 10.4 (1H, s, minor), 8.91 (1H, s, major), 8.87 (1H, d, J = 7.8 Hz), 8.49 (1H, s, minor), 8.45 (1H, d, J = 9.0 Hz, minor), 8.22 (1H, d, J = 8.4 Hz, major), 7.56−7.48 (2H, m, minor), 7.45−7.30 (9H, m, major), 6.62 (1H, m, major), 6.02 (1H, brs, minor), 5.24 (1H, m, minor), 4.67 (1H, brs, major), 4.61 (1H, q, J = 8.4 Hz, minor), 4.50 (1H, q, J = 3.6 Hz, minor), 4.43 (1H, brs, major), 4.32 (1H, brs, major), 4.11 (1H, m, major), 4.02 (1H, m, major), 3.78 (1H, m, minor), 3.66 (1H, m, minor), 3.53 (1H, m, major), 3.43 (1H, m, major), 3.29 (3H, s, major), 3.17 (1H, m, major), 3.03 (1H, dd, J = 14.7, 8.7 Hz, minor), 2.77 (3H, s, minor), 2.32 (1H, m, major), 2.24 (1H, m, minor), 2.15−1.90 (4H, m, major), 1.86−1.60 (6H, m, major), 1.53 (2H, m, major), 1.43−1.22 (7H, m, major), 1.04−0.87 (12H, m); 13C NMR (150 MHz, CDCl3) δ 173.7, 173.5, 172.9, 172.1, 171.4, 170.9, 170.5, 170.3, 170.2, 170.0, 169.4, 138.2, 136.3, 136.2, 134.4, 131.1, 130.3, 129.4, 129.0, 128.9, 128.3, 128.2, 127.2, 127.1, 126.8, 126.5, 125.6, 124.3, 123.7, 65.4, 59.0, 58.0, 57.6, 54.9, 54.3, 51.5, 49.9, 45.5, 39.1, 37.8, 37.0, 36.1, 36.0, 29.7, 26.65, 26.60, 25.5, 25.4, 25.0, 23.6, 23.4, 23.3, 23.1, 23.1, 23.0, 22.9, 22.1, 18.4, 16.8, 16.6, 14.3, 14.0, 11.7, 11.6; IR (neat) 3334, 3008, 2960, 2934, 2873, 1668, 1616, 1585, 1520, 1450, 1403, 1294, 1278, 1266, 754, 666 cm−1; [α]26 D −106 11459

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry (400 MHz, CDCl3) δ 9.44 (1H, s), 8.29 (1H, d, J = 8.3 Hz), 8.23 (1H, d, J = 8.0 Hz), 7.66 (1H, d, J = 9.8 Hz), 7.47 (1H, m), 7.39 (3H, m), 7.48 (1H, m), 7.27 (2H, t, J = 7.6 Hz), 7.24−7.18 (3H, m), 7.15 (1H, m), 4.71 (1H, m), 4.65 (1H, m), 4.44 (1H, dd, J = 7.6, 3.2 Hz), 4.16 (1H, d, J = 13.9, 3.7 Hz), 3.74 (1H, m), 3.52 (1H, q, J = 4.6 Hz), 3.38 (1H, dd, J = 14.3, 5.2 Hz), 3.27 (1H, dd, J = 14.4, 9.8 Hz), 3.23 (3H, s), 3.16 (1H, dd, J = 13.2, 2.2 Hz), 2.42 (1H, m), 2.29 (1H, m), 2.16 (3H, m), 2.04 (1H, m), 2.15 (1H, m), 1.69 (2H, m), 1.59 (2H, m), 1.36 (4H, m), 1.25 (3H, d, J = 7.3 Hz), 1.01 (6H, t, J = 6.2 Hz), 0.97− 0.87 (6H, m); 13C NMR (100 MHz, CDCl3) δ 174.4, 173.4, 170.8, 170.2, 169.0, 168.9, 138.3, 137.0, 131.7, 129.5, 128.2, 127.0, 126.3, 124.0, 123.4, 122.8, 65.4, 61.5, 57.3, 54.6, 52.6, 47.7, 37.90, 37.89, 33.9, 28.0, 27.4, 26.8, 25.6, 24.5, 23.3, 22.1, 18.2, 13.9, 11.7; IR (neat) 3339, 3336, 2959, 2935, 2873, 1683, 1641, 1618, 1594, 1539, 1520, 1506, 1450, 1435, 1292, 754, 701, 680, 667 cm−1; [α]27 D −7.00 (c 0.650, CHCl3); HRMS (ESI/IT) calcd for C38H52N6O6Na [M + Na]+ 711.3841, found 711.3826. 13 (D-Ala → D-MeAla): yield 55% (28.0 mg, 39.3 μmol) over 13 steps from Fmoc-D-MeAla-Lantern; a white amorphous solid; 1H NMR (600 MHz, CDCl3) δ 8.39 (1H, brs), 8.13 (1H, s), 7.40 (1H, s), 7.31−7.10 (8H, m), 6.72 (1H, brs), 5.24 (1H, m), 5.10 (1H, m), 4.86 (2H, m), 4.64 (1H, brs), 3.59−3.39 (3H, m), 3.29 (3H, s), 2.94 (3H, s), 2.54 (1H, t, J = 12.9 Hz), 2.19−1.88 (6H, m), 1.73 (4H, m), 1.60 (3H, m), 1.36 (1H, m), 1.22 (3H, d, J = 7.2 Hz), 1.06−1.00 (6H, m), 0.93 (3H, d, J = 6.0 Hz), 0.89 (3H, t, J = 7.5 Hz); 13C NMR (150 MHz, CDCl3) δ 175.2, 173.2, 172.5, 172.2, 171.7, 171.4, 170.7, 169.5, 168.0, 137.0, 136.5, 135.8, 134.5, 130.6, 130.1, 129.1, 128.9, 128.7, 127.6, 127.2, 126.9, 126.2, 125.9, 124.7, 124.3, 123.4, 123.2, 122.4, 59.4, 58.1, 56.7, 56.1, 55.7, 54.4, 54.1, 53.7, 51.7, 50.4, 45.3, 43.8, 40.4, 39.5, 36.9, 36.2, 36.0, 35.6, 32.3, 31.5, 30.5, 29.8, 28.7, 26.7, 26.4, 26.3, 25.8, 25.7, 24.3, 23.9, 23.3, 21.2, 19.5, 18.3, 15.4, 14.6, 14.0, 12.5, 11.8, 11.6; IR (neat) 3355, 2959, 2935, 1691, 1647, 1637, 1617, 1585, 1522, 1507, 1499, 1452, 1419, 1405, 753 cm−1; [α]26 D −61.9 (c 1.35, CHCl3); HRMS (ESI/IT) calcd for C39H54N6O6Na [M + Na]+ 725.3997, found 725.3981. 14 (L-MeLeu → L-Leu): yield 27% (14.9 mg, 22.1 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (600 MHz, CDCl3) δ 9.24 (1H, s), 7.94 (1H, s), 7.44−7.27 (7H, m), 7.20 (2H, m), 7.15 (1H, t, J = 7.8 Hz), 7.22−6.83 (1H, m), 4.71 (1H, m), 4.55−4.40 (2H, m), 4.37 (1H, brs), 4.10 (1H, brs), 3.71 (1H, m), 3.45 (1H, m), 3.29 (1H, dd, J = 13.8, 4.8 Hz), 3.02 (1H, m), 2.36− 2.13 (2H, m), 2.00 (1H, m), 1.91 (2H, m), 1.81 (1H, brs), 1.66 (2H, m), 1.60−1.50 (2H, m), 1.40 (1H, brs), 1.24 (1H, m), 1.27−1.16 (4H, m), 0.98 (3H, d, J = 6.6 Hz), 0.91 (3H, d, J = 6.6 Hz), 0.89−0.84 (6H, m); 13C NMR (150 MHz, CDCl3) δ 172.9, 172.4, 171.6, 170.9, 170.5, 137.2, 135.8, 131.1, 129.1, 128.6, 127.2, 126.7, 124.2, 124.0, 58.7, 58.3, 55.0, 53.3, 49.5, 48.3, 38.5, 36.1, 36.0, 26.7, 26.4, 26.3, 25.0, 23.2, 22.7, 21.5, 18.4, 16.7, 14.4, 11.8, 11.4; IR (neat) 3311, 3010, 2960, 2936, 2873, 1654, 1647, 1586, 1534, 1450, 1427, 1298, 1278, 1267, 1237, 754, 701, 667 cm−1; [α]26 D −9.60 (c 0.725, CHCl3); HRMS (ESI/IT) calcd for C37H50N6O6Na [M + Na]+ 697.3684, found 697.3667. 15 (Ant → MeAnt): yield 25% (13.8 mg, 19.6 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (600 MHz, CDCl3) δ 7.91 (1H, brs), 7.53 (1H, m), 7.45 (1H, t, J = 7.2 Hz), 7.38 (1H, d, J = 7.8 Hz), 7.35 (1H, d, J = 7.8 Hz), 7.25−7.18 (5H, m), 7.02 (1H, d, J = 7.2 Hz), 6.93 (1H, d, J = 7.2 Hz), 5.28 (1H, s), 4.78 (1H, m), 4.49 (1H, m), 4.33 (1H, m), 3.93 (1H, m), 3.76 (1H, m), 3.67 (1H, m), 3.39 (1H, m), 3.26 (3H, s), 3.23 (3H, s), 2.20 (3H, m), 1.90 (2H, m), 1.84 (1H, m), 1.74−1.53 (4H, m), 1.39 (1H, d, J = 7.8 Hz), 1.37−1.17 (3H, m), 1.07−0.88 (8H, m), 0.81 (3H, d, J = 6.6 Hz), 0.65 (3H, t, J = 7.2 Hz); 13C NMR (150 MHz, CDCl3) δ 173.9, 172.5, 171.8, 171.6, 171.0, 169.3, 140.7, 138.0, 131.0, 130.6, 129.8, 129.5, 129.1, 128.7, 128.4, 128.3, 128.2, 128.1, 126.3, 54.0, 53.2, 53.1, 51.2, 48.3, 45.0, 43.0, 39.5, 39.4, 38.0, 37.5, 37.3, 37.1, 27.5, 25.4, 25.3, 24.2, 22.7, 22.5, 21.7, 19.3, 16.9, 14.0, 11.9; IR (neat) 3293, 3007, 2960, 2937, 2873, 1652, 1645, 1634, 1505, 1495, 1454, 1388, 1282, 1255, 1240, 1218, 1134, 753, 700, 666 cm−1; [α]26 D −34.4 (c 0.660, CHCl3); HRMS (ESI/IT) calcd for C39H54N6O6Na [M + Na]+ 725.3997, found 725.3981.

16 (D-allo-Ile → D-allo-MeIle): yield 24% (12.3 mg, 17.5 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (600 MHz, CDCl3) δ 8.46 (1H, d, J = 8.4 Hz), 8.31 (1H, d, J = 9.6 Hz), 8.95 (1H, s), 7.37 (1H, m), 7.25−7.06 (7H, m), 6.93 (1H, d, J = 7.8 Hz), 5.26 (1H, t, J = 5.1 Hz), 5.02 (1H, q, J = 6.0 Hz), 4.86 (1H, d, J = 10.8 Hz), 4.73 (1H, m), 4.47 (1H, t, J = 6.9 Hz), 3.85 (1H, dt, J = 12.6, 3.6 Hz), 3.51 (1H, m), 2.96 (2H, m), 2.82 (3H, s), 2.71 (3H, s), 2.21 (1H, m), 2.08−1.80 (5H, m), 1.75−1.60 (4H, m), 1.52 (1H, m), 1.44 (1H, m), 1.34 (3H, d, J = 7.2 Hz), 1.09 (1H, m), 1.02−0.93 (9H, m), 0.58 (3H, d, J = 6.0 Hz); 13C NMR (150 MHz, CDCl3) δ 173.2, 171.6, 171.3, 171.1, 169.4, 169.2, 168.8, 168.5, 135.8, 135.7, 130.6, 129.6, 128.6, 128.3, 127.0, 126.8, 125.2, 123.8, 121.7, 61.8, 58.4, 50.8, 49.7, 48.6, 44.8, 38.9, 38.2, 37.9, 37.7, 31.9, 30.3, 28.8, 26.9, 26.7, 25.9, 25.7, 25.0, 23.9, 23.4, 23.3, 22.6, 22.0, 18.7, 17.1, 14.5, 11.6; IR (neat) 3340, 2960, 2934, 2872, 1652, 1623, 1602, 1587, 1521, 1450, 1410, 1289, 754, 701, 665 cm−1; [α]26 D +50.5 (c 0.590, CHCl3); HRMS (ESI/IT) calcd for C39H54N6O6Na [M + Na]+ 725.4003, found 725.3980. 17 (L-Phe → L-MePhe): yield 24% (9.5 mg, 13.5 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (600 MHz, CDCl3) δ 9.04 (1H, s), 7.90 (1H, d, J = 8.4 Hz), 7.38 (2H, m), 7.29−7.17 (5H, m), 7.17 (1H, m), 6.89 (1H, d, J = 5.4 Hz), 6.67 (1H, d, J = 7.2 Hz), 5.81 (1H, d, J = 6.0 Hz), 5.48 (1H, q, J = 5.7 Hz), 4.78 (1H, m), 4.54 (1H, m), 4.11 (2H, m), 3.75 (1H, m), 3.53 (1H, m), 3.30−3.19 (3H, m), 3.13 (1H, m), 3.06 (3H, s), 2.93 (1H, m), 2.86 (3H, s), 2.24−2.07 (3H, m), 1.97−1.80 (3H, m), 1.75−1.55 (7H, m), 1.52−1.32 (4H, m), 1.25 (1H, m), 1.06−0.91 (6H, m), 0.84 (3H, d, J = 6.6 Hz), 0.76 (3H, d, J = 6.6 Hz); 13C NMR (150 MHz, CDCl3) δ 176.6, 173.6, 172.9, 172.4, 171.5, 170.7, 17.5, 170.0, 169.9, 169.8, 169.4, 168.2, 136.3, 134.9, 130.3, 129.2, 128.78, 128.75, 128.66, 128.62, 128.55, 128.4, 127.7, 126.9, 126.6, 126.5, 126.2, 124.4, 123.8, 58.7, 58.3, 57.8, 56.8, 56.0, 55.7, 52.9, 47.1, 46.6, 46.2, 45.8, 45.4, 43.3, 39.5, 37.9, 37.7, 37.5, 37.0, 36.4, 36.0, 35.2, 32.8, 32.2, 32.0, 31.6, 30.2, 29.7, 29.2, 28.9, 28.6, 27.1, 26.8, 26.3, 26.3, 26.26, 26.0, 25.7, 25.0, 24.4, 24.1, 23.7, 23.4, 23.2, 23.0, 2.3, 22.2, 21.5, 19.0, 18.6, 18.1, 17.4, 17.0, 14.8, 14.4, 13.5, 11.8, 11.7, 11.6; IR (neat) 3337, 3008, 2958, 2936, 2872, 1685, 1636, 1622, 1597, 1507, 1451, 1418, 1278, 1218, 753, 700, 666 cm−1; [α]26 D −305.6 (c 0.450, CHCl3); HRMS (ESI/IT) calcd for C39H54N6O6Na [M + Na]+ 725.3997, found 725.3979. 18 (Ant → β-Ala): yield 50% (17.2 mg, 26.8 μmol) over 13 steps from Fmoc-D-Ala-OH; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 8.14 (1H, d, J = 7.6 Hz), 7.96 (1H, d, J = 9.3 Hz), 7.36−7.16 (6H, m), 6.54 (1H, d, J = 8.8 Hz), 4.67 (1H, m), 4.56 (1H, dd, J = 14.0, 7.7 Hz), 4.27 (1H, m), 4.03 (1H, dd, J = 12.9, 10.5 Hz), 3.82 (1H, d, J = 13.4 Hz), 3.72 (1H, d, J = 8.0 Hz), 3.55 (1H, dd, J = 8.3, 5.6 Hz), 3.29 (1H, dd, J = 14.1, 5.4 Hz), 3.16 (3H, s), 3.14−2.98 (3H, m), 2.53 (2H, m), 2.11 (4H, m), 1.92 (1H, m), 1.74 (1H, m), 1.60 (3H, m), 1.42 (3H, d, J = 7.3 Hz), 1.35−1.22 (2H, m), 0.98 (6H, t, J = 6.0 Hz), 0.87 (3H, t, J = 7.3 Hz), 0.82 (3H, d, J = 6.8 Hz); 13C NMR (100 MHz, CDCl3) δ 174.4, 171.9, 171.4, 171.2, 170.9, 170.1, 169.4, 137.9, 129.4, 129.0, 128.6, 126.3, 65.4, 59.9, 56.9, 48.1, 48.0, 38.7, 37.5, 35.1, 34.9, 33.9, 33.7, 33.6, 28.6, 26.7, 25.6, 25.0, 23.5, 21.7, 18.2, 14.0, 11.72, 11.67; IR (neat) 3436, 3306, 3006, 2959, 2935, 2873, 1646, 1521, 1456, 1412, 1369, 1247, 753, 700, 666 cm−1; [α]26 D +18.5 (c 0.825, CHCl3); HRMS (ESI/IT) calcd for C34H52N6O6Na [M + Na]+ 663.3841, found 663.3828. 19 (Ant → 3-Abz): yield 26% (9.0 mg, 13.1 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 8.86 (1H, s), 8.34 (1H, d, J = 8.5 Hz), 7.63 (1H, brs), 7.36 (1H, t, J = 7.9 Hz), 7.27 (2H, t, J = 7.3 Hz), 7.24−7.15 (4H, m), 7.02 (1H, t, J = 7.6 Hz), 6.46 (1H, s), 5.93 (1H, s), 4.86−4.78 (2H, m), 4.68 (1H, d, J = 13.4 Hz), 4.36 (1H, d, J = 5.4 Hz), 4.08 (1H, m), 3.59 (2H, m), 3.23 (1H, m), 2.86 (1H, t, J = 12.8 Hz), 2.66 (3H, s), 2.31 (1H, t, J = 10.6 Hz), 2.12 (1H, m), 1.78 (1H, d, J = 10.5 Hz), 1.75−1.55 (4H, m), 1.45−1.20 (5H, m), 1.18 (3H, d, J = 6.8 Hz), 0.95 (6H, d, J = 7.5 Hz), 0.92 (3H, m), 0.78 (3H, d, J = 6.8 Hz); 13C NMR (100 MHz, CDCl3) δ 173.8, 172.9, 172.1, 171.3, 170.5, 170.4, 138.1, 137.7, 135.7, 130.2, 129.0, 128.4, 126.7, 122.3, 121.3, 115.1, 64.3, 58.2, 55.1, 53.5, 51.6, 40.0, 39.6, 37.9, 36.8, 35.5, 27.4, 26.5, 25.4, 24.6, 23.8, 21.5, 19.5, 16.4, 14.6, 11.8; IR (neat) 3331, 2958, 2934, 1683, 1660, 11460

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

4 h, the reaction mixture was quenched with AcOH and then concentrated in vacuo. The residue was dissolved in EtOAc, washed with saturated aq NaHCO3 and brine, dried over MgSO4, and then concentrated in vacuo. The residue was purified with RP-HPLC (column, YMC-Pack R&D ODS-A 20 mm × 150 mm; flow rate, 12.0 mL/min; elution method, H2O/MeOH = 25:75 to 20:80 linear gradient (0.0−20.0 min)) to afford 22 (16.1 mg, 21.1 μmol, 40% from polymer-supported Fmoc-D-Ala-OH (4)) as a white amorphous solid: 1 H NMR (400 MHz, CDCl3) δ 9.12 (1H, s), 8.31 (1H, d, J = 8.0 Hz), 8.23 (1H, d, J = 8.0 Hz), 7.39 (3H, m), 7.35 (3H, m), 7.22 (3H, m), 7.13 (3H, m), 6.78 (1H, m), 6.54 (1H, brs), 6.21 (1H, d, J = 6.8 Hz), 5.28 (2H, m), 5.07 (1H, brs), 4.90 (1H, m), 4.82 (1H, m), 4.67 (1H, m), 4.57 (1H, t, J = 6.8 Hz), 4.48 (1H, m), 4.39 (1H, m), 3.71 (3H, s), 3.64 (3H, s), 3.12 (3H, s), 3.07 (3H, m), 2.88 (2H, s), 2.29 (1H, m), 2.13 (2H, m), 1.94 (4H, s), 1.80−1.45 (8H, m), 1.45−1.20 (9H, m), 1.03 (6H, dd, J = 6.6, 3.9 Hz), 0.93 (3H, d, J = 6.1 Hz), 0.87−0.81 (9H, m), 0.75 (3H, d, J = 6.6 Hz), 0.72 (3H, d, J = 6.8 Hz); 13C NMR (100 MHz, CDCl3) δ 173.5, 173.1, 172.9, 172.6, 171.6, 171.0, 170.8, 170.7, 170.4, 170.3, 169.9, 169.6, 169.1, 136.9, 136.5, 135.0, 134.8, 130.3, 130.0, 129.2, 129.1, 128.7, 128.6, 127.0, 126.9, 126.3, 126.1, 124.2, 124.0, 122.7, 121.3, 58.5, 57.7, 57.3, 54.8, 54.7, 54.5, 52.21, 52.18, 48.6, 48.1, 44.8, 38.9, 38.7, 37.9, 37.0, 30.7, 29.4, 26.3, 25.5, 25.2, 25.0, 24.4, 23.7, 23.3, 23.21, 23.20, 23.16, 22.6, 22.0, 19.4, 17.4, 16.7, 14.5, 14.1, 11.9, 11.6; IR (neat) 3311, 3306, 3006, 2958, 2939, 2874, 1747, 1654, 1624, 1587, 1534, 1453, 1405, 1386, 1283, 1207, 1159, 755, 700, 666 cm−1; [α]26 D −107 (c 0.550, CHCl3); HRMS (ESI/ IT) calcd for C41H58N6O8Na [M + Na]+ 785.4208, found 785.4191. Assay of Paralytic Activity against Larvae of Silkworms by Hemolymph Injection. The eggs of silkworm Bombyx mori were purchased from Kougensha Co, Ltd. (Matsumoto, Japan) and cultured on an artificial diet, SilkMate 2S, obtained from the Nosan Corporation. Each PF1171 peptide was dissolved in DMSO at concentrations of 5 mM. A total of 2 μL of each solution was injected into open vessels of third-instar larvae, resulting in the dose of 10.0 nmol/larva. A total of 20 larvae were injected with each dilution, and the number of paralyzed larvae was counted 1 h after the injection. We confirmed that the paralyzed silkworms were alive and creeping 24 h later, indicating that the paralysis is reversible. Assay of Paralytic Activity against Larvae of Silkworms by Oral Administration. The eggs of silkworm Bombyx mori were purchased from Kougensha Co, Ltd. (Matsumoto, Japan) and cultured on an artificial diet, SilkMate 2S, obtained from the Nosan Corporation. To 2 g of the diet was added 0.2 mg of each PF1171 analogue in acetone (200 μL) on a Petri dish. After removing the solvent, 10 larvae at the third-instar stage were introduced to each Petri dish. The behavior of the silkworms was then observed. Parallel Artificial Membrane Permeability Assay. The permeability of the PF1171 peptides through an artificial membrane was evaluated using a Corning Gentest Precoated PAMPA Plate System (Corning Inc. Corning, NY, USA) according to the manufacturer’s instructions. Briefly, each PF1171 analogue was dissolved in DMSO at 2 mM. After a 20-fold dilution in phosphate buffered saline (10 mM sodium phosphate containing 140 mM NaCl at pH 6.8), the resultant solution (100 μM peptide, including 5% DMSO) was added to the wells (300 μL/well) of the receiver plate (donor plate) and PBS (without peptide, including 5% DMSO) was added to the wells (200 μL/well) of the precoated filter plate (acceptor plate). The filter plate was then coupled with the receiver plate, and the plate assembly was incubated at 25 °C without agitation for 5 h. At the end of the incubation, the plates were separated and 150 μL of solution from each well of both plates was collected and frozen. The sample solutions were thawed right before they were subjected to HPLC analysis. After centrifugation at 15 000 rpm for 3 min, 50 μL of the supernatant was analyzed by RP-HPLC (column, YMC-Pack ODS-A 4.6 mm × 150 mm; flow rate, 1.0 mL/min; elution method, H2O/CH3CN = 50:50 to 5:95 linear gradient (0.0−20.0 min)). The area of absorption at 254 nm was integrated. The permeability of the compounds was calculated using the following formula:

1653, 1647, 1608, 1539, 1527, 1489, 1455, 1404, 1314, 751, 701, 668 cm−1; [α]26 D −53.9 (c 0.425, CHCl3); HRMS (ESI/IT) calcd for C38H52N6O6Na [M + Na]+ 711.3841, found 711.3826. 20 (L-Pip → L-Pro): yield 30% (13.2 mg, 19.6 μmol) over 13 steps from Fmoc-D-Ala-OH; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 8.94 (1H, s, minor), 8.71 (1H, s), 8.61 (1H, d, J = 9.2 Hz), 8.31 (1H, s, minor), 8.18 (1H, d, J = 8.2 Hz, minor), 7.97 (1H, d, J = 8.5 Hz), 7.76 (1H, d, J = 8.2 Hz, minor), 7.63 (1H, d, J = 7.0 Hz, minor), 7.51 (1H, d, J = 9.2 Hz, minor), 7.39 (1H, t, J = 8.4 Hz), 7.32−7.16 (4H, m), 7.11 (3H, m), 6.96−6.79 (2H, m, minor), 6.65 (1H, d, J = 8.5 Hz), 6.40 (1H, m, minor), 6.08 (1H, m), 4.92 (1H, d, J = 7.2 Hz), 4.75 (1H, m), 4.66 (1H, m), 4.58−4.40 (2H, m), 4.28 (1H, t, J = 10.1 Hz), 4.06−3.84 (3H, m, minor), 3.63 (1H, m), 3.56 (1H, m, minor), 3.45 (1H, m, minor), 3.36 (1H, m, minor), 3.33 (3H, s, minor), 3.00 (1H, m), 2.96 (3H, s), 2.79 (3H, s, minor), 2.36−2.14 (4H, m), 2.10−1.85 (6H, m), 1.77 (1H, s), 1.55 (1H, m), 1.28 (4H, m), 1.17 (2H, m), 1.05−0.58 (12H, m); 13C NMR (100 MHz, CDCl3) δ 171.9, 171.1, 170.7, 170.1, 169.7, 168.6, 136.1, 135.9, 135.2, 131.3, 130.9, 130.4, 129.4, 129.3, 129.0, 128.7, 128.6, 128.3, 127.1, 127.0, 125.6, 123.6, 60.2, 58.6, 56.3, 55.8, 51.1, 48.4, 38.2, 36.8, 35.2, 30.5, 29.8, 29.0, 25.9, 24.9, 24.3, 23.3, 22.1, 17.1, 13.9, 11.8; IR (neat) 3299, 2961, 2934, 1687, 1683, 1662, 1653, 1645, 1619, 1159, 1515, 1454, 1418, 1295, 754, 700, 666 cm−1; [α]26 D −29.6 (c 0.625, CHCl3); HRMS (ESI/IT) calcd for C37H50N6O6Na [M + Na]+ 697.3684, found 697.3665. 21 (L-Pip → L-MeAla): yield 37% (17.6 mg, 26.6 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (400 MHz, CDCl3) δ 9.96 (1H, s), 8.31 (1H, d, J = 8.3 Hz), 8.12 (1H, d, J = 8.0 Hz), 7.48 (1H, t, J = 7.4 Hz), 7.44−7.33 (4H, m), 7.28 (2H, d, J = 7.4 Hz), 7.21 (2H, m), 7.13 (1H, t, J = 7.6 Hz), 4.67 (2H, m), 4.50 (1H, dd, J = 7.9, 3.0 Hz), 3.81 (1H, q, J = 6.6 Hz), 3.52 (1H, d, J = 8.5, 4.9 Hz), 3.39 (1H, dd, J = 14.4, 4.9 Hz), 3.29 (1H, m), 3.25 (6H, m), 2.44 (1H, m), 2.35 (1H, m), 2.00 (1H, m), 1.72 (1H, m), 1.60 (3H, d, J = 6.6 Hz), 1.43−1.25 (3H, m), 1.19 (3H, d, J = 7.3 Hz), 1.01 (6H, t, J = 6.2 Hz), 0.91 (6H, m); 13C NMR (100 MHz, CDCl3) δ 174.3, 173.3, 170.9, 170.0, 169.7, 138.2, 137.6, 132.0, 129.5, 128.3, 127.1, 126.4, 123.7, 122.7, 121.2, 65.5, 59.5, 57.1, 54.7, 47.6, 38.9, 38.2, 38.1, 26.8, 25.7, 23.2, 22.2, 18.4, 13.9, 13.6, 11.7; IR (neat) 3312, 3008, 2961, 2934, 2874, 1683, 1645, 1618, 1593, 1516, 1455, 1443, 1411, 1387, 1320, 1295, 1089, 754, 702, 668 cm−1; [α]26 D −3.50 (c 0.850, CHCl3); HRMS (ESI/IT) calcd for C36H50N6O6Na [M + Na]+ 685.3684, found 685.3667. 23 (a PF1171F dimer analogue bearing 4-Abz instead of Ant, chemical structure found in Figure S4): yield 9% (6.0 mg, 4.35 μmol) over 13 steps from Fmoc-D-Ala-Lantern; a white amorphous solid; 1H NMR (600 MHz, CDCl3) δ 8.64 (2H, s), 8.26 (2H, d, J = 5.4 Hz), 7.57 (4H, d, J = 8.4 Hz), 7.43 (4H, d, J = 8.4 Hz), 7.30−7.19 (12H, m), 6.08 (2H, d, J = 10.2 Hz), 4.75 (2H, dd, J = 8.4, 5.4 Hz), 4.67 (2H, dd, J = 9.6, 3.6 Hz), 4.20 (4H, m), 3.90 (2H, m), 3.71 (2H, m), 3.60 (2H, dd, J = 9.6, 3.6 Hz), 3.47 (6H, s), 3.44 (2H, m), 3.05 (2H, dd, J = 13.2, 4.2 Hz), 2.21 (2H, m), 2.05 (6H, m), 1.87 (4H, m), 1.75 (2H, m), 1.60 (4H, m), 1.25 (4H, m), 0.98 (6H, d, J = 6.6 Hz), 0.95 (6H, d, J = 6.6 Hz), 0.71 (6H, m), 0.64 (12H, m); 13C NMR (150 MHz, CDCl3) δ 175.1, 174.1, 173.4, 170.4, 170.2, 169.8, 139.5, 136.8, 129.9, 129.5, 128.5, 128.2, 126.7, 120.3, 65.9, 57.8, 56.4, 53.1, 50.3, 44.5, 40.7, 38.1, 36.0, 35.3, 29.7, 26.1, 25.5, 24.4, 23.6, 22.8, 21.7, 18.1, 15.2, 14.0, 11.7; IR (neat) 3308, 2959, 2934, 1654, 1647, 1610, 1522, 1455, 1404, 1389, 1246, 753, 700 cm−1; [α]26 D −34.3 (c 0.275, CHCl3); HRMS (ESI/IT) calcd for C76H105N12O12 [MH]+ 1377.7969, found 1377.7941. Synthesis of Linear Peptide 22. The hexapeptide-supported Lantern (Ac-L-Phe−D-allo-Ile−Ant−L-Pip−L-MeLeu−D-Ala−trityl alcohol Lantern) was treated with 30% HFIP/CH2Cl2 (1.00 mL/ Lantern) at room temperature. After being shaken for 1 h, the reaction mixture was filtered and the lantern was washed with CH2Cl2 (3 min × 3). The combined filtrate was concentrated in vacuo, and the crude Nacetyl hexapeptide was used without further purification. The crude hexapeptide (34.6 mg) was dissolved in Et2O (460 μL) and MeOH (460 μL) and treated with 2 M TMSCHN2 in Et2O (116 μL, 231 μmol) at 0 °C. After being stirred at the same temperature for 11461

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry

(12) Walsh, C. T.; Zydowsky, L. D.; McKeon, F. D. J. Biol. Chem. 1992, 267, 13115. (13) Augustijns, P. F.; Bradshaw, T. P.; Gan, L. S. L.; Hendren, R. W.; Thakker, D. R. Biochem. Biophys. Res. Commun. 1993, 197, 360. (14) Jin, L.; Harrison, S. C. Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 13522. (15) Ko, S. Y.; Dalvit, C. Int. J. Pept. Protein Res. 1992, 40, 380. (16) Augustijns, P. F.; Brown, S. C.; Willard, D. H.; Consler, T. G.; Annaert, P. P.; Hendren, R. W.; Bradshaw, T. P. Biochemistry 2000, 39, 7621. (17) Wenger, R. M.; France, J.; Bovermann, G.; Walliser, L.; Widmer, A.; Widmer, H. FEBS Lett. 1994, 340, 255. (18) Loosli, H.-R.; Kessler, H.; Oschkinat, H.; Weber, H.-P.; Petcher, T. J.; Widmer, A. Helv. Chim. Acta 1985, 68, 682. (19) Kessler, H.; Köck, M.; Wein, T.; Gehrke, M. Helv. Chim. Acta 1990, 73, 1818. (20) Rezai, T.; Bock, J. E.; Zhou, M. V.; Kalyanaraman, C.; Lokey, R. S.; Jacobson, M. P. J. Am. Chem. Soc. 2006, 128, 14073. (21) Hewitt, W. M.; Leung, S. S.; Pye, C. R.; Ponkey, A. R.; Bednarek, M.; Jacobson, M. P.; Lokey, R. S. J. Am. Chem. Soc. 2015, 137, 715. (22) Beck, J. G.; Chatterjee, J.; Laufer, B.; Kiran, M. U.; Frank, A. O.; Neubauer, S.; Ovadia, O.; Greenberg, S.; Gilon, C.; Hoffman, A.; Kessler, H. J. Am. Chem. Soc. 2012, 134, 12125. (23) Nielsen, D. S.; Hoang, H. N.; Lohman, R. J.; Hill, T. A.; Lucke, A. J.; Craik, D. J.; Edmonds, D. J.; Griffith, D. A.; Rotter, C. J.; Ruggeri, R. B.; Price, D. A.; Liras, S.; Fairlie, D. P. Angew. Chem., Int. Ed. 2014, 53, 12059. (24) Wang, C. K.; Northfield, S. E.; Colless, B.; Chaousis, S.; Hamernig, I.; Lohman, R. J.; Nielsen, D. S.; Schroeder, C. I.; Liras, S.; Price, D. A.; Fairlie, D. P.; Craik, D. J. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 17504. (25) Bockus, A. T.; McEwen, C. M.; Lokey, R. S. Curr. Top. Med. Chem. 2013, 13, 821. (26) Ahlbach, C. L.; Lexa, K. W.; Bockus, A. T.; Chen, V.; Crews, P.; Jacobson, M. P.; Lokey, R. S. Future Med. Chem. 2015, 7, 2121. (27) Wang, C. K.; Craik, D. J. Biopolymers 2016, 106, 901. (28) Nielsen, D. S.; Shepherd, N. E.; Xu, W.; Lucke, A. J.; Stoermer, M. J.; Fairlie, D. P. Chem. Rev. 2017, 117, 8094. (29) Umagome, K.; Nagase, K.; Harimaya, K.; Nakayama, F.; Yaguchi, T.; Satou, E.; Hoshiko, S.; Kamitoo, N.; Soneda, T.; Hachisu, M. (Meiji Seika Kaisha, Ltd., Japan). p 28. Jpn. JPH1121297(A), 1999. (30) Igarashi, Y.; Hanafusa, T.; Gohda, F.; Peterson, S.; Bills, G. Mycology 2014, 5, 102. (31) Igarashi, Y.; Gohda, F.; Kadoshima, T.; Fukuda, T.; Hanafusa, T.; Shojima, A.; Nakayama, J.; Bills, G. F.; Peterson, S. J. Antibiot. (Tokyo) 2015, 68, 707. (32) Liermann, J. C.; Thines, E.; Anke, H.; Opatz, T. Z. Naturforsch., B: J. Chem. Sci. 2009, 64, 727. (33) Kai, K.; Yoshikawa, H.; Kuo, Y. H.; Akiyama, K.; Hayashi, H. Biosci., Biotechnol., Biochem. 2010, 74, 1309. (34) Kuo, Y.-H.; Kai, K.; Akiyama, K.; Hayashi, H. Tetrahedron Lett. 2012, 53, 429. (35) Prompanya, C.; Fernandes, C.; Cravo, S.; Pinto, M. M. M.; Dethoup, T.; Silva, A. M. S.; Kijjoa, A. Mar. Drugs 2015, 13, 1432. (36) Ha, S. D.; Nagata, S.; Suzuki, A.; Kataoka, H. Peptides 1999, 20, 561. (37) Nakahara, Y.; Kanamori, Y.; Kiuchi, M.; Kamimura, M. Arch. Insect Biochem. Physiol. 2003, 52, 163. (38) Ishii, K.; Hamamoto, H.; Kamimura, M.; Sekimizu, K. J. Biol. Chem. 2008, 283, 2185. (39) Ishii, K.; Hamamoto, H.; Kamimura, M.; Nakamura, Y.; Noda, H.; Imamura, K.; Mita, K.; Sekimizu, K. J. Biol. Chem. 2010, 285, 28635. (40) Ishii, K.; Hamamoto, H.; Imamura, K.; Adachi, T.; Shoji, M.; Nakayama, K.; Sekimizu, K. J. Biol. Chem. 2010, 285, 33338. (41) Masuda, Y.; Tanaka, R.; Kai, K.; Ganesan, A.; Doi, T. J. Org. Chem. 2014, 79, 7844.

Permeability (cm/s): Pe = {− ln[1 − CA(t )/Ceq ]}/[A × (1/VD + 1/VA ) × t ] where A = filter area (0.3 cm2), VD = donor well volume (0.3 mL), VA = acceptor well volume (0.2 mL), t = incubation time (seconds), CA(t) = compound concentration in acceptor well at time t, CD(t) = compound concentration in donor well at time t, and Ceq = [CD(t) × VD + CA(t) × VA]/(VD + VA).

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01975. Paralytic activity, distance and dihedral angle constraints, atomic coordinates, reaction conditions for solid-phase peptide elongation, chemical shifts of amide protons at various temperatures, H/D exchange NMR experiments, lowest-energy structures of the major conformers, chemical structure of 23, and copies of 1H and 13C NMR spectra (PDF)

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Takayuki Doi: 0000-0002-8306-6819 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by JSPS KAKENHI, Grant nos. JP26850068 (Grant-in-Aid for Young Scientists (B)) and JP15H05837 (Grant-in-Aid for Scientific Research on Innovative Areas: Middle Molecular Strategy).

■

REFERENCES

(1) Katsara, M.; Tselios, T.; Deraos, S.; Deraos, G.; Matsoukas, M. T.; Lazoura, E.; Matsoukas, J.; Apostolopoulos, V. Curr. Med. Chem. 2006, 13, 2221. (2) Howell, S. M.; Fiacco, S. V.; Takahashi, T. T.; Jalali-Yazdi, F.; Millward, S. W.; Hu, B.; Wang, P.; Roberts, R. W. Sci. Rep. 2014, 4, 6008. (3) Rezai, T.; Yu, B.; Millhauser, G. L.; Jacobson, M. P.; Lokey, R. S. J. Am. Chem. Soc. 2006, 128, 2510. (4) Price, D. A.; Eng, H.; Farley, K. A.; Goetz, G. H.; Huang, Y.; Jiao, Z.; Kalgutkar, A. S.; Kablaoui, N. M.; Khunte, B.; Liras, S.; Limberakis, C.; Mathiowetz, A. M.; Ruggeri, R. B.; Quan, J. M.; Yang, Z. Org. Biomol. Chem. 2017, 15, 2501. (5) Zorzi, A.; Deyle, K.; Heinis, C. Curr. Opin. Chem. Biol. 2017, 38, 24. (6) Kessler, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 512. (7) Masuda, Y.; Suzuki, J.; Onda, Y.; Fujino, Y.; Yoshida, M.; Doi, T. J. Org. Chem. 2014, 79, 8000. (8) Yoshida, M.; Onda, Y.; Masuda, Y.; Doi, T. Biopolymers (Pept. Sci.) 2016, 106, 404. (9) Onda, Y.; Masuda, Y.; Yoshida, M.; Doi, T. J. Med. Chem. 2017, 60, 6751. (10) Kopple, K. D.; Go, A.; Schamper, T. J.; Wilcox, C. S. J. Am. Chem. Soc. 1973, 95, 6090. (11) Over, B.; McCarren, P.; Artursson, P.; Foley, M.; Giordanetto, F.; Gronberg, G.; Hilgendorf, C.; Lee, M. D. t.; Matsson, P.; Muncipinto, G.; Pellisson, M.; Perry, M. W.; Svensson, R.; Duvall, J. R.; Kihlberg, J. J. Med. Chem. 2014, 57, 2746. 11462

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463

Article

The Journal of Organic Chemistry (42) Masuda, Y.; Tanaka, R.; Ganesan, A.; Doi, T. J. Nat. Prod. 2015, 78, 2286. (43) Matsumori, N.; Kaneno, D.; Murata, M.; Nakamura, H.; Tachibana, K. J. Org. Chem. 1999, 64, 866. (44) Mohamadi, F.; Richards, N. G. J.; Guida, W. C.; Liskamp, R.; Lipton, M.; Caufield, C.; Chang, G.; Hendrickson, T.; Still, W. C. J. Comput. Chem. 1990, 11, 440. (45) Still, W. C.; Tempczyk, A.; Hawley, R. C.; Hendrickson, T. J. Am. Chem. Soc. 1990, 112, 6127. (46) Schrödinger Suite 2012: MacroModel, version 9.9; Schrödinger, LLC: New York, 2012. (47) Qiu, D.; Shenkin, P. S.; Hollinger, F. P.; Still, W. C. J. Phys. Chem. A 1997, 101, 3005. (48) Gellman, S. H.; Dado, G. P.; Liang, G. B.; Adams, B. R. J. Am. Chem. Soc. 1991, 113, 1164. (49) Tsang, K. Y.; Diaz, H.; Graciani, N.; Kelly, J. W. J. Am. Chem. Soc. 1994, 116, 3988. (50) Wagner, G.; Pardi, A.; Wuethrich, K. J. Am. Chem. Soc. 1983, 105, 5948. (51) Wishart, D. S.; Sykes, B. D.; Richards, F. M. J. Mol. Biol. 1991, 222, 311. (52) Wahyudi, H.; Tantisantisom, W.; Liu, X.; Ramsey, D. M.; Singh, E. K.; McAlpine, S. R. J. Org. Chem. 2012, 77, 10596. (53) Rasoul, F.; Ercole, F.; Pham, Y.; Bui, C. T.; Wu, Z. M.; James, S. N.; Trainor, R. W.; Wickham, G.; Maeji, N. J. Biopolymers (Pept. Sci.) 2000, 55, 207. (54) Frérot, E.; Coste, J.; Pantaloni, A.; Dufour, M.-N.; Jouin, P. Tetrahedron 1991, 47, 259. (55) Falb, E.; Yechezkel, T.; Salitra, Y.; Gilon, C. J. Pept. Res. 1999, 53, 507. (56) Carpino, L. A. J. Am. Chem. Soc. 1993, 115, 4397. (57) Tidgewell, K.; Engene, N.; Byrum, T.; Media, J.; Doi, T.; Valeriote, F. A.; Gerwick, W. H. ChemBioChem 2010, 11, 1458. (58) Chen, Q. Y.; Liu, Y.; Luesch, H. ACS Med. Chem. Lett. 2011, 2, 861. (59) Thornburg, C. C.; Cowley, E. S.; Sikorska, J.; Shaala, L. A.; Ishmael, J. E.; Youssef, D. T.; McPhail, K. L. J. Nat. Prod. 2013, 76, 1781. (60) Wu, W.-J.; Raleigh, D. P. J. Org. Chem. 1998, 63, 6689. (61) Kansy, M.; Senner, F.; Gubernator, K. J. Med. Chem. 1998, 41, 1007. (62) Glaser, R. W. J. Gen. Physiol. 1925, 7, 599. (63) Jameson, A. P.; Atkins, W. R. G. Biochem. J. 1921, 15, 209. (64) Chatterjee, J.; Gilon, C.; Hoffman, A.; Kessler, H. Acc. Chem. Res. 2008, 41, 1331. (65) Kwon, Y. U.; Kodadek, T. Chem. Biol. 2007, 14, 671. (66) Eguchi, M.; Kuriyama, K. J. Biochem. 1985, 97, 1437. (67) Hamamoto, K.; Kida, Y.; Zhang, Y.; Shimizu, T.; Kuwano, K. Microbiol. Immunol. 2002, 46, 741. (68) Fiacco, S. V.; Roberts, R. W. ChemBioChem 2008, 9, 2200.

11463

DOI: 10.1021/acs.joc.7b01975 J. Org. Chem. 2017, 82, 11447−11463