Synthesis of Sterically Fixed Phytochrome Chromophore Derivatives

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Cite This: J. Org. Chem. 2018, 83, 10743−10748

Synthesis of Sterically Fixed Phytochrome Chromophore Derivatives Bearing a 15E-Fixed or 15E-Anti-Fixed CD-Ring Component Takahiro Soeta,* Nobuhiko Ohashi, Toshiharu Kobayashi, Yoko Sakata, Takuya Suga, and Yutaka Ukaji* Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan

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ABSTRACT: To analyze the structure and function of phytochrome chromophores, we have been synthesizing natural and unnatural bilin chromophores of phytochromes. In this manuscript, we report the synthesis of sterically fixed 15E-f ixed 18Et-biliverdin (BV) and 15E-anti-fixed 18Et-BV derivatives. The key reaction is the introduction of an sp3 carbon alkyl chain bearing a leaving group at the mesoposition of the CD-ring component by using the corresponding Grignard reagents in the presence of LiCl.

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the E isomer at the C15C16 double bond between the pyrrole rings C and D. To analyze the structure and function of the chromophores in the phytochromes, we focused on the stereochemistry around the C15 position and studied the synthesis of natural and unnatural bilin chromophores, such as phytochromobilin (PΦB), phycocyanobilin (PCB), biliverdin (BV), and unnatural modified chromophores.7 In addition, we successfully synthesized the sterically locked 15Z-syn, 15Z-anti, 15E-syn, and 15E-anti 18Et-BV derivatives, which made it possible to confirm the stereochemistry around the C15 position of the chromophores in Agrobacteium phytochromes Agp1 (Figure 2). As a result of assembly experiments of the synthetic chromophores with phytochrome apoproteins in vitro, we determined the stereochemistry at the C15 position of the chromophores in the Pr- and Pfr-states of Agp1 as 15Z-anti and 15E-anti, respectively.7 Furthermore, we synthesized the locked 15Z-anti and 15E-anti PCB, which were assembled in vivo with the phytochrome in Ceratodon purpureus. The feeding induced chlorophyll accumulation, modulation of gravitropism, and induction of side branches in darkness, which revealed that the 15E-anti stereochemistry of the chromophore resulted in the formation of the active Pfr-state phytochrome in the cell.8 In contrast, the synthesis of sterically fixed chromophores at the meso-position could be crucial, especially those with configurations and conformations separately locked in order to explore the detailed dynamic mechanisms of photoconversion of the phytochrome chromophores.9 For the synthesis of meso-

INTRODUCTION Phytochromes are photoreceptors1 in plants and microorganisms such as bacteria,2 fungi,3 and simple molds.4 They are composed of photosensory input and regulatory output modules and function as bimodal photoswitches. Phytochromes play critical roles in various light-regulated processes, ranging from phototaxis and pigmentation in bacteria to seed germination, chloroplast development, shade avoidance, and flowering in higher plants. Phytochromes have open-chain tetrapyrrole chromophores (bilin), for example, phytochromobilin (PΦB), phycocyanobilin (PCB), and biliverdin (BV) in plant, cyanobacterial, and other bacterial phytochromes, respectively. The photosensor is interconverted between two states to activate or deactivate the attached output module. Upon light absorption, the linear tetrapyrrole cofactor undergoes isomerization through photoconversion between the red light-absorbing state (Pr) and the far-red lightabsorbing state (Pfr) (Figure 1).5,6 It is generally accepted that the photochemical reaction is followed by thermal relaxation steps, in which the first step is interconversion from the Z to

Figure 1. Interconversion between the Pr and Pfr states in the case of BV-type chromophore. © 2018 American Chemical Society

Received: May 15, 2018 Published: August 21, 2018 10743

DOI: 10.1021/acs.joc.8b01252 J. Org. Chem. 2018, 83, 10743−10748

Article

The Journal of Organic Chemistry

Scheme 1. Retrosynthetic Analysis of Sterically Fixed Phytochrome Chromophore Derivatives 1 and 2

Figure 2. Sterically locked BV derivatives.

fixed chromophores, regioselective introduction of an alkyl group using organomagnesium reagents with a mesobrominated CD ring could be effective. By using this methodology, we synthesized the 15E-f ixed 18Et-BV derivative as a simple model of a phytochrome chromophore by the use of functionalized vinylic Grignard reagents.10 However, it was difficult to prepare the functionalized vinylic Grignard reagents for the synthesis of 15E-f ixed 18Et-BV derivatives. In addition, the conjugation system of the prepared 15E-f ixed 18Et-BV derivatives differed from the natural BV derivatives because of the newly introduced double bond in the fixed moiety. Furthermore, ring closure by the C-ring nitrogen atom to produce 15anti-f ixed CD ring derivatives was unsuccessful. To solve these problems, we investigated the installation of an sp3 carbon functionality onto the C15 meso-carbon. Herein, we report the syntheses of l5E-f ixed 18Et-BV and 15E-anti-f ixed 18Et-BV-type chromophores by the introduction of an sp3 alkyl chain at the meso-position as a key step by the use of sp3 hybridized Grignard reagents in the presence of LiCl. The retrosynthetic analysis is shown in Scheme 1. In the synthesis of sterically fixed 15E-f ixed 18Et-BV 1 or 15E-antif ixed 18Et-BV 2, the chemoselective ring closure reaction was carried out by an intramolecular SN2 reaction of the nitrogen atom of the D- or C-ring toward the alkyl halide moiety tethered at the C15 position. Regioselective introduction of the alkyl group using Grignard reagents with meso-brominated CD ring component 3 could be employed.

(entry 1). In the absence of LiCl, the chemical yield of (E)-5a was decreased (entry 2). A diethyl ether solution of ethylmagnesium bromide (4a′) (3.0 M in Et2O) was not effective in this reaction, affording the product in 30% yield (entry 3). Although other additives such as magnesium halides or CuCl were also investigated, we found that LiCl was the best in this reaction (entries 4−7). Decreasing the amount of LiCl (3.0 equiv and 1.0 equiv) afforded lower yields of (E)-5a (entries 8 and 9). Having established a method for the introduction of the alkyl group into the meso position of the CD ring, we then set out to evaluate the effectiveness of various Grignard reagents in the presence of LiCl (entries 10− 15). When methylmagnesium bromide (4b) or butylmagnesium bromide (4c) was used, the respective products (E)-5b and (E)-5c were obtained in high yields (entries 10 and 11). The stereochemistry of (E)-5c was determined by X-ray crystallography.11 The chemical yield of (E)-5d was moderate, perhaps because of the steric hindrance of isopropylmagnesium bromide (4d) (entry 12).12 Vinylmagnesium bromide and phenylmagnesium bromide bearing sp2 carbons were also applicable to this reaction, affording the products in moderate to good yields (entries 13 and 14). To synthesize sterically fixed CD-ring components tethered to the meso-position, introduction of a substituent bearing an ω-leaving group, Cl(CH2)4MgBr (4g), was examined.13 The reactivity was rather low, and the product (E)-5g was obtained in 46% yield after 6 h (entry 15). The stereochemistry of (E)5g was determined by X-ray crystallography.14 Next, we investigated the cyclization reaction of the alkyl substituent at the meso position by the nitrogen atom of the D-

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RESULTS AND DISCUSSION We initially examined whether Grignard reagents bearing sp3 carbon alkyl chains were capable of participating in the coupling reaction with the meso-brominated CD ring. In our initial studies, we used starting material (Z)-3 with ethylmagnesium bromide (4a) (1.0 M in THF) (3.0 equiv) in the presence of LiCl (5.0 equiv) as an additive in CH2Cl2 at room temperature (entry 1, Table 1).10 The reaction proceeded smoothly to afford the meso-ethylated dipyrrinone (E)-5a in 89% yield stereoselectively after 2 h, irrespective of the presence of allyl and tert-butyl ester moieties in the molecule 10744

DOI: 10.1021/acs.joc.8b01252 J. Org. Chem. 2018, 83, 10743−10748

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The Journal of Organic Chemistry

reaction, giving the E-anti-f ixed CD-ring component 7 in 11% yield (entry 3). After several attempts, we found that 2.0 equiv of KOt-Bu was effective in this reaction, giving the E-anti-f ixed CD-ring component 7 in 29% yield (entry 4). The coupling reaction between the CD- and AB-ring components 6 and 816 was carried out under acidic conditions to afford the sterically fixed 18Et-BV diallyl ester derivative 9 bearing the 15E-f ixed CD-ring component in 62% yield (1).

Table 1. Introduction of Alkyl Group at the C15 Position

entrya

R1−MgBr 4

additive

yield of (E)-5/%

1 2 3 4 5 6 7 8b 9c 10 11 12 13 14 15d,e

EtMgBr (1.0 M in THF) (4a) EtMgBr (1.0 M in THF) (4a) EtMgBr (3.0 M in Et2O) (4a′) EtMgBr (1.0 M in THF) (4a) EtMgBr (1.0 M in THF) (4a) EtMgBr (1.0 M in THF) (4a) EtMgBr (1.0 M in THF) (4a) EtMgBr (1.0 M in THF) (4a) EtMgBr (1.0 M in THF) (4a) MeMgBr (0.9 M in THF) (4b) n-BuMgBr (0.73 M in THF) (4c) i-PrMgBr (0.88 M in THF) (4d) vinylMgBr (1.0 M in THF) (4e) PhMgBr (1.1 M in THF) (4f) Cl(CH2)4MgBr (1.7 M in THF) (4g)

LiCl − LiCl MgCl2 MgI2 ZnCl2 CuCl LiCl LiCl LiCl LiCl LiCl LiCl LiCl LiCl

89 (E)-(5a) 66 (E)-(5a) 30 (E)-(5a) 60 (E)-(5a) 67 (E)-(5a) 67(E)-(5a) 45 (E)-(5a) 63 (E)-(5a) 45 (E)-(5a) 98 (E)-(5b) 94 (E)-(5c) 52 (E)-(5d) 75 (E)-(5e) 54 (E)-(5f) 46 (E)-(5g)

Under the same conditions, sterically 15E-anti-f ixed 18Et-BV diallyl ester derivative 10 was obtained in 16% yield using CDand AB-ring components 7 and 8 as starting materials (eq 2).

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a The reaction was carried out using 5.0 equiv of 4 and 3.0 equiv of LiCl for 3 h unless otherwise mentioned. bIn this reaction, 3.0 equiv of LiCl was used. cIn this reaction, 1.0 equiv of LiCl was used. dThe reaction was quenched after 6 h. eByproduct (E)-5c was obtained in 20% yield.

CONCLUSIONS In conclusion, the synthesis of sterically fixed 15E-fixed 18EtBV and 15E-antifixed 18Et-BV derivatives was achieved. The introduction of an sp3 carbon alkyl chain at the meso-position by treatment of the corresponding Grignard reagents in the presence of LiCl was a key step. The prepared chromophores will facilitate the investigation of the stereochemistries and functions of phytochrome chromophores both in vitro and in vivo. The synthesis of other types of sterically fixed chromophores is now in progress in our laboratory.

or C-ring using a base (Table 2). When (E)-5g was treated with NaH in the presence of tetrabutylammonium iodide (TBAI), a chemoselective intramolecular SN2 reaction of the D-ring nitrogen atom to the alkyl side chain provided the Eanti-fixed CD-ring component 6 in 61% yield (entry 1). The structure of 6 was unambiguously determined by X-ray crystallography.15 We were pleased to find that when KH was used as a base, the cyclization by the C-ring nitrogen atom proceeded to afford E-f ixed CD-ring component 7 in 21% yield in addition to 6 (entry 2). KOt-Bu was also applicable to this

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EXPERIMENTAL SECTION

General. 1H NMR spectra were recorded on a 400 MHz NMR spectrometer. Chemical shifts δ are reported in ppm using TMS as an internal standard. Data are reported as follows: chemical shift,

Table 2. Cyclization Reactions of Chlorobutyl-Substituted (E)-5g

entry

base

yield of 6/%

yield of 7/%

1 2 3 4a

NaH KH KOt-Bu KOt-Bu

61 61 54 54

− 21 11 29

a

Here, 2.0 equiv of KOt-Bu was used. 10745

DOI: 10.1021/acs.joc.8b01252 J. Org. Chem. 2018, 83, 10743−10748

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The Journal of Organic Chemistry

6H), 1.31 (s, 3H), 1.57 (s, 9H), 1.91 (s, 3H), 2.27 (q, J = 8.0 Hz, 2H), 2.53−2.60 (m, 2H), 2.80−2.87 (m, 1H), 2.99−3.07 (m, 2H), 4.58 (d, J = 6.0 Hz, 2H), 5.22 (d, J = 9.2 Hz, 1H), 5.30 (d, J = 16.8 Hz, 1H), 5.87−5.97 (m, 1H), 7.46 (brs, 1H), 8.51 (brs, 1H). 13C NMR (CDCl3): 9.7, 10.7, 13.2, 16.6, 20.8, 21.0, 21.7, 28.4, 32.0, 35.3, 65.0, 81.1, 118.2, 119.8, 120.4, 127.2, 128.2, 132.2, 136.4, 137.5, 140.8, 161.2, 171.1, 172.7. IR (KBr): 3320, 2930, 1740, 1690, 1460, 1370, 1270, 1170 cm −1 . HRMS−DART (m/z): Calcd for C27H39N2O5 [M + H]+: 471.2859. Found: 471.2857. tert-Butyl (E)-3-(3-(Allyloxy)-3-oxopropyl)-5-(1-(4-ethyl-3-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)allyl)-4-methyl-1H-pyrrole-2-carboxylate (5e). Silica gel column chromatography (hexane/ diethyl ether = 1/2) gave 5e (20 mg, 75% yield, 0.06 mmol scale) as a brown oil. 1H NMR (CDCl3): 0.99 (t, J = 7.6 Hz, 3H), 1.34 (s, 3H), 1.51 (s, 9H), 1.78 (s, 3H), 2.25 (q, J = 7.6 Hz, 2H), 2.51 (t, J = 7.6 Hz, 2H), 2.98 (t, J = 7.6 Hz, 2H), 4.51 (d, J = 5.6 Hz, 2H), 4.92 (d, J = 16.4 Hz, 1H), 5.17 (d, J = 11.2 Hz, 1H), 5.24 (d, J = 16.8 Hz, 1H), 5.29 (d, J = 11.2 Hz, 1H), 5.81−5.88 (m, 1H), 6.61 (dd, J = 16.8, 11.2 Hz, 1H), 7.62 (brs, 1H), 8.83 (brs, 1H). 13C NMR (CDCl3): 9.0, 10.7, 13.2, 16.8, 20.9, 28.4, 35.4, 65.0, 81.1, 113.7, 118.2, 120.0, 120.1, 120.3, 126.6, 128.5, 132.2, 132.4, 137.0, 138.8, 140.7, 161.0, 171.7, 172.7. IR (KBr): 3430, 2980, 1650, 1460, 1370, 1270, 1160 cm−1. HRMS−DART (m/z): Calcd for C26H35N2O5 [M + H]+: 455.2546. Found: 455.2554. tert-Butyl (E)-3-(3-(Allyloxy)-3-oxopropyl)-5-((4-ethyl-3-methyl5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)(phenyl)methyl)-4-methyl1H-pyrrole-2-carboxylate (5f). Silica gel column chromatography (hexane/diethyl ether = 1/1) gave 5f (16 mg, 54% yield, 0.06 mmol scale) as a brown oil. 1H NMR (CDCl3): 1.09 (t, J = 7.2 Hz, 3H), 1.25 (s, 3H), 1.58 (s, 9H), 1.74 (s, 3H), 2.35 (q, J = 7.2 Hz, 2H), 2.57 (t, J = 7.2 Hz, 2H), 3.03 (t, J = 7.2 Hz, 2H), 4.57 (d, J = 6.0 Hz, 2H), 5.23 (d, J = 12.0 Hz, 1H), 5.30 (d, J = 16.8 Hz, 1H), 5.79−5.88 (m, 1H), 7.21−7.35 (m, 6H), 8.75 (brs, 1H). 13C NMR (CDCl3): 9.1, 11.1, 13.1, 16.9, 20.8, 28.4, 35.3, 65.0, 81.3, 114.6, 118.2, 120.6, 121.1, 128.4, 128.7, 129.0, 129.4, 129.5, 132.2, 137.3, 138.0, 138.2, 140.2, 160.8, 171.1, 172.7. IR (KBr): 3450, 2920, 1740, 1650, 1460, 1370, 1270, 1160 cm−1. HRMS−DART (m/z): Calcd for C30H37N2O5 [M + H]+: 505.2702. Found: 505.2715. tert-Butyl (E)-3-(3-(Allyloxy)-3-oxopropyl)-5-(5-chloro-1-(4-ethyl3-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)pentyl)-4-methyl1H-pyrrole-2-carboxylate (5g). Silica gel column chromatography (hexane/diethyl ether = 2/3) gave 5g (47 mg, 46% yield, 0.2 mmol scale) as a white solid of mp = 180−181 °C (hexane/ethyl acetate). 1 H NMR (CDCl3): 1.05 (t, J = 7.2 Hz, 3H), 1.42 (s, 3H), 1.49−1.53 (m, 2H), 1.56 (s, 9H), 1.82−1.89 (m, 2H), 1.91 (s, 3H), 2.29 (q, J = 7.2 Hz, 2H), 2.49−2.59 (m, 4H), 3.02 (t, J = 7.2 Hz, 2H), 3.54 (t, J = 6.4 Hz, 2H), 4.58 (d, J = 6.0 Hz, 2H), 5.24 (d, J = 10.4 Hz, 1H), 5.32 (d, J = 16.4 Hz, 1H), 5.87−5.97 (m, 1H), 8.86 (brs, 1H), 9.50 (brs, 1H). 13C NMR (CDCl3): 9.3, 10.9, 13.2, 16.6, 20.9, 25.8, 28.4, 32.3, 33.8, 35.2, 44.7, 65.0, 81.1, 115.5, 118.2, 119.4, 119.8, 128.5, 130.0, 132.2, 136.4, 138.9, 140.0, 161.1, 172.5, 172.7. IR (KBr): 3300, 2930, 1740, 1690, 1460, 1370, 1270, 1160 cm−1. HRMS−DART (m/z): Calcd for C28H40N2O5Cl [M + H]+: 519.2626. Found: 519.2616. Cyclization Reaction of (E)-5g by the Use of Sodium Hydride. To a solution of (E)-5g (28 mg, 0.054 mmol) and tetrabutylammonium iodide (26 mg, 0.072 mmol) in THF (28 mL), sodium hydride (60% dispersion in mineral oil, 2.8 mg, 0.072 mmol) was added at room temperature, and the whole was stirred for 1 h. Satd. NH4Cl aq (10 mL) was added, and the organic layer was separated. The aqueous layer was extracted with ethyl acetate (7 mL × 3), and the combined organic layers were washed with satd. NaHCO3 aq and brine. Concentration and the subsequent purification by silica gel column chromatography were used to afford the cyclized product 6. tert-Butyl 3-(3-(Allyloxy)-3-oxopropyl)-5-(2-ethyl-1-methyl-3oxo-5,6,7,8-tetrahydro-3H-pyrrolo[1,2-a]azepin-9-yl)-4-methyl-1Hpyrrole-2-carboxylate (6). Silica gel column chromatography (hexane/diethyl ether = 1/1) gave 6 (16 mg, 61% yield, 0.054 mmol scale) as a white solid of mp = 130−132 °C (hexane/ethyl acetate). 1H NMR (CDCl3): 1.05 (t, J = 6.8 Hz, 3H), 1.35 (s, 3H), 1.57 (s, 9H), 1.92 (s, 3H), 1.92−1.97 (m, 4H), 2.33 (q, J = 6.8 Hz,

multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), coupling constant (J), and integration. 13C NMR spectra were recorded on 100 MHz NMR spectrometer. The chemical shifts were determined in the δ-scale relative to CDCl3 (δ = 77.0 ppm). The wave numbers of maximum absorption peaks of IR spectroscopy are presented in cm−1. HRMS (direct analysis in real time (DART) and ESI) was measured with TOF mass spectrometers. All melting points were measured using a micromelting point apparatus. Dehydrated solvents were purchased for the reactions and were used without further desiccation. Introduction of Alkyl Group at the C15 Position (Table 1). To a solution of (Z)-310 (30 mg, 0.06 mmol) and LiCl (13 mg, 0.3 mmol) in CH2Cl2 (8.0 mL), Grignard reagent (0.18 mmol) was added at 0 °C. After the reaction mixture was stirred at room temperature for 2−3 h, satd. NH4Cl aq was added. The organic layer was separated, and the aqueous layer was extracted with ethyl acetate (8 mL × 3). The combined organic layers were washed with saturated (satd.) NaHCO3 aq and brine and then were dried over Na2SO4. Concentration and the subsequent purification by silica gel column chromatography were used to afford the desired product. tert-Butyl (E)-3-(3-(Allyloxy)-3-oxopropyl)-5-(1-(4-ethyl-3-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)propyl)-4-methyl-1H-pyrrole-2-carboxylate (5a). Silica gel column chromatography (hexane/ ethyl acetate = 2/1) gave 5a (24 mg, 89% yield, 0.06 mmol scale) as a brown solid of mp = 140−142 °C (hexane/ethyl acetate). 1H NMR (CDCl3): 0.92−0.99 (m, 6H), 1.34 (s, 3H), 1.50 (s, 9H), 1.87 (s, 3H), 2.22 (q, J = 7.2 Hz, 2H), 2.35 (q, J = 7.6 Hz, 2H), 2.49 (t, J = 7.6 Hz, 2H), 2.95 (t, J = 7.6 Hz, 2H), 4.49 (d, J = 5.6 Hz, 2H), 5.15 (d, J = 10.4 Hz, 1H), 5.24 (d, J = 17.2 Hz, 1H), 5.86−5.97 (m, 1H), 7.90 (broad singlet (brs), 1H), 8.70 (brs, 1H). 13C NMR (CDCl3): 9.2, 10.9, 12.7, 13.2, 16.7, 20.9, 27.5, 28.4, 35.3, 65.0, 81.1, 118.2, 119.4, 119.8, 128.5, 129.6, 132.2, 136.4, 137.9, 140.2, 161.0, 171.4, 172.8. IR (KBr): 3310, 2970, 1740, 1660, 1460, 1370, 1280, 1130 cm−1. HRMS−DART (m/z): Calcd for C26H37N2O5 [M + H]+: 457.2702. Found: 457.2694. tert-Butyl (E)-3-(3-(Allyloxy)-3-oxopropyl)-5-(1-(4-ethyl-3-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)ethyl)-4-methyl-1H-pyrrole-2-carboxylate (5b). Silica gel column chromatography (hexane/ ethyl acetate = 2/1) gave 5b (29 mg, 98% yield, 0.06 mmol scale) as a brown oil. 1H NMR (CDCl3): 0.97 (t, J = 7.2 Hz, 3H), 1.37 (s, 3H), 1.49 (s, 9H), 1.86 (s, 3H), 2.09 (s, 3H), 2.22 (q, J = 7.2 Hz, 2H), 2.49 (t, J = 7.2 Hz, 2H), 2.95 (t, J = 7.2 Hz, 2H), 4.51 (d, J = 5.6 Hz, 2H), 5.16 (d, J = 10.0 Hz, 1H), 5.24 (d, J = 16.8 Hz, 1H), 5.82 (ddt, J = 16.8, 10.0, 5.6 Hz, 1H), 8.44 (brs, 1H), 9.00 (brs, 1H). 13C NMR (CDCl3): 9.1, 11.0, 13.2, 16.6, 20.3, 20.9, 28.4, 35.3, 65.0, 81.1, 118.1, 118.6, 119.6, 128.8, 131.2, 132.2, 136.9, 138.5, 140.0, 161.1, 171.8, 172.8. IR (KBr): 3300, 2970, 1740, 1660, 1450, 1370, 1280, 1170 cm−1. HRMS−DART (m/z): Calcd for C25H35N2O5 [M + H]+: 443.2546. Found: 443.2539. tert-Butyl (E)-3-(3-(Allyloxy)-3-oxopropyl)-5-(1-(4-ethyl-3-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)pentyl)-4-methyl-1H-pyrrole-2-carboxylate (5c).10 Silica gel column chromatography (hexane/ethyl acetate = 2/1) gave 5c (27 mg, 94% yield, 0.06 mmol scale) as a brown solid of mp = 155−156 °C (hexane/ethyl acetate). 1H NMR (CDCl3): 0.87 (t, J = 6.8 Hz, 3H), 1.04 (t, J = 7.2 Hz, 3H), 1.35−1.36 (m, 4H), 1.41 (s, 3H), 1.56 (s, 9H), 1.90 (s, 3H), 2.29 (q, J = 7.2 Hz, 2H), 2.41−2.43 (m, 2H), 2.59 (t, J = 8.4 Hz, 2H), 3.01 (t, J = 8.4 Hz, 2H), 4.58 (d, J = 5.6 Hz, 2H), 5.24 (d, J = 10.4 Hz, 1H), 5.32 (d, J = 17.2 Hz, 1H), 5.87−5.97 (m, 1H), 8.75 (brs, 1H), 8.97 (brs, 1H). 13C NMR (CDCl3): 9.3, 10.9, 13.2, 13.9, 16.6, 20.9, 22.8, 28.3, 30.5, 34.5, 35.3, 65.0, 81.1, 116.0, 118.2, 119.3, 119.7, 128.4, 130.3, 132.2, 136.2, 138.3, 140.0, 161.2, 171.9, 172.8. IR (KBr): 3300, 2980, 1740, 1660, 1460, 1370, 1270, 1160 cm−1. HRMS−DART (m/z): Calcd for C28H41N2O5 [M + H]+: 485.3015. Found: 485.3011. tert-Butyl (E)-3-(3-(Allyloxy)-3-oxopropyl)-5-(1-(4-ethyl-3-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)-2-methylpropyl)-4methyl-1H-pyrrole-2-carboxylate (5d). Silica gel column chromatography (hexane/diethyl ether = 2/3) gave 5d (14 mg, 52% yield, 0.06 mmol scale) as a brown solid of mp = 156−159 °C (hexane/ethyl acetate). 1H NMR (CDCl3): 0.95 (d, J = 6.4 Hz, 3H), 1.03−1.07 (m, 10746

DOI: 10.1021/acs.joc.8b01252 J. Org. Chem. 2018, 83, 10743−10748

Article

The Journal of Organic Chemistry 2H), 2.57 (t, J = 8.4 Hz, 2H), 2.65 (brs, 2H), 3.02 (t, J = 8.4 Hz, 2H), 3.84 (brs, 1H), 3.93 (brs, 1H), 4.58 (d, J = 4.8 Hz, 2H), 5.23 (d, J = 10.4 Hz, 1H), 5.32 (d, J = 17.6 Hz, 1H), 5.87−5.97 (m, 1H), 8.61 (brs, 1H). 13C NMR (CDCl3): 9.3, 10.7, 13.3, 17.0, 20.8, 24.7, 26.2, 28.4, 32.8, 35.2, 39.8, 65.0, 81.1, 117.0, 118.2, 119.2, 119.7, 128.8, 132.0, 132.2, 135.2, 138.8, 143.4, 160.8, 171.2, 172.7. IR (KBr): 3310, 2930, 1740, 1690, 1460, 1370, 1290, 1160 cm−1. HRMS−DART (m/ z): Calcd for C28H39N2O5 [M + H]+: 483.2859. Found: 483.2842. Cyclization Reactions (E)-5g by the Use of Potassium tertButoxide. To a solution of (E)-5g (30 mg, 0.06 mmol) and tetrabutylammonium iodide (27 mg, 0.08 mmol) in THF (28 mL), potassium tert-butoxide (13 mg, 0.12 mmol) was added at room temperature, and the whole was stirred for 1 h. Satd. NH4Cl aq (10 mL) was added, and the organic layer was separated. The aqueous layer was extracted with ethyl acetate (7 mL × 3), and the combined organic layers were washed with satd. NaHCO3 aq and brine. Concentration and the subsequent purification by silica gel column chromatography were used to afford the desired products 6 and 7. tert-Butyl (E)-2-(3-(Allyloxy)-3-oxopropyl)-9-(4-ethyl-3-methyl-5oxo-1,5-dihydro-2H-pyrrol-2-ylidene)-1-methyl-6,7,8,9-tetrahydro5H-pyrrolo[1,2-a]azepine-3-carboxylate (7). Silica gel column chromatography (hexane/diethyl ether = 1/1) gave 7 (8 mg, 29% yield, 0.06 mmol scale) as a white solid of mp = 150−153 °C (hexane/ethyl acetate). 1H NMR (CDCl3): 1.08 (t, J = 7.2 Hz, 3H), 1.56 (s, 3H), 1.59 (s, 9H), 1.62−1.66 (m, 3H), 1.73−1.84 (m, 1H), 1.86 (s, 3H), 2.17−2.24 (m, 1H), 2.33 (q, J = 7.2 Hz, 2H), 2.47−2.57 (m, 4H), 2.90−2.98 (m, 1H), 3.03−3.08 (m, 1H), 3.59−3.66 (m, 1H), 4.58 (d, J = 5.6 Hz, 2H), 5.24 (d, J = 10.4 Hz, 1H), 5.32 (d, J = 17.6 Hz, 1H), 5.87−5.97 (m, 1H), 7.20 (brs, 1H). 13C NMR (CDCl3): 9.5, 11.3, 13.2, 16.7, 21.8, 25.9, 27.8, 28.4, 31.3, 35.5, 45.0, 64.9, 80.0, 115.2, 117.9, 118.1, 119.2, 128.9, 132.3, 135.4, 136.3, 137.2, 140.3, 161.2, 171.4, 172.9. IR (KBr): 3420, 2930, 1740, 1690, 1460, 1370, 1290, 1160 cm−1. HRMS−DART (m/z): Calcd for C28H39N2O5 [M + H]+: 483.2859. Found: 483.2854. Allyl 3-(2-((Z)-(3-(3-(Allyloxy)-3-oxopropyl)-4-methyl-5-((Z)-(4methyl-5-oxo-3-vinyl-1,5-dihydro-2H-pyrrol-2-ylidene)methyl)-2Hpyrrol-2-ylidene)methyl)-5-(2-ethyl-1-methyl-3-oxo-5,6,7,8-tetrahydro-3H-pyrrolo[1,2-a]azepin-9-yl)-4-methyl-1H-pyrrol-3-yl)propanoate (9). The mixture of 6 (43 mg, 0.09 mmol) and 8 (31 mg, 0.09 mmol) was dissolved with TFA (1.5 mL) at room temperature, and the whole was stirred at room temperature for 30 min. The reaction mixture was diluted with methanol (3.0 mL), and the whole was stirred for 1 h. After removing the solvent in vacuo, the residue was purified by silica gel column chromatography (hexane/ethyl acetate = 2/1) and gave 9 (43 mg, 62% yield) as a violet amorphous solid. 1H NMR (CDCl3): 1.00 (t, J = 7.2 H, 3H), 1.45 (s, 3H), 1.88− 2.07 (m, 4H), 1.95 (s, 3H), 2.05 (s, 3H), 2.07 (s, 3H), 2.28 (q, J = 7.2 Hz, 2H), 2.60 (t, J = 7.2 Hz, 4H), 2.67−2.73 (m, 1H), 2.94−3.08 (m, 5H), 3.85−3.90 (m, 1H), 3.98−4.03 (m, 1H), 4.57 (d, J = 6.4 Hz, 2H), 4.58 (d, J = 7.6 Hz, 2H), 5.27 (d, J = 10.4 Hz, 2H), 5.27−5.32 (m, 2H), 5.66 (d, J = 11.6 Hz, 1H), 5.68 (d, J = 18.0 Hz, 1H), 5.83− 5.94 (m, 2H), 6.03 (s, 1H), 6.62 (dd, J = 18.0, 11.6 Hz, 1H), 6.88 (s, 1H). Two NH protons were not observed cleanly. 13C NMR (CDCl3): 9.7, 9.8, 11.1, 13.2, 17.1, 19.9, 20.0, 25.1, 26.4, 29.7, 32.9, 35.3, 35.4, 40.2, 65.27, 65.29, 98.1, 116.2, 116.8, 118.3, 118.4, 121.7, 122.6, 126.2, 129.4, 129.9, 132.05, 132.08, 132.3, 133.2, 135.4, 138.3, 139.9, 142.0, 142.6, 144.1, 148.6, 164.6, 171.1, 171.2, 172.26, 172.31. IR (KBr): 3450, 2920, 1740, 1650, 1560, 1460, 1370, 1260, 1160 cm−1. UV−vis (CHCl3): λmax 378 (ε = 28600), 594 (ε = 14600) nm. HRMS−DART (m/z): Calcd for C43H51N4O6 [M + H]+: 719.3809. Found: 719.3821. Allyl 3-((E)-3-((Z)-(3-(3-(Allyloxy)-3-oxopropyl)-4-methyl-5-((Z)(4-methyl-5-oxo-3-vinyl-1,5-dihydro-2H-pyrrol-2-ylidene)methyl)2H-pyrrol-2-ylidene)methyl)-9-(4-ethyl-3-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)-1-methyl-6,7,8,9-tetrahydro-5H-pyrrolo[1,2-a]azepin-2-yl)propanoate (10). The mixture of 7 (54 mg, 0.11 mmol) and 8 (40 mg, 0.11 mmol) was dissolved with TFA (2.0 mL) at room temperature, and the whole was stirred at room temperature for 30 min. The reaction mixture was diluted with methanol (3.0 mL), and the whole was stirred for 1 h. After removing the solvent in vacuo, the residue was purified by silica gel column chromatography

(hexane/ethyl acetate = 2/1) and gave 10 (13 mg, 16% yield) as a violet amorphous solid. 1H NMR (CDCl3): 1.03 (t, J = 7.6 Hz, 3H), 1.58 (s, 3H), 1.59−1.96 (m, 4H), 1.86 (s, 3H), 1.97 (s, 3H), 2.02 (s, 3H), 2.16−2.22 (m, 1H), 2.28 (q, J = 7.6 Hz, 2H), 2.44 (t, J = 7.2 Hz, 2H), 2.53 (t, J = 7.2 Hz, 2H), 2.76−2.80 (m, 1H), 2.85−3.04 (m, 4H), 3.70 (t, J = 12.4 Hz, 1H), 4.41 (d, J = 6.0 Hz, 2H), 4.50 (d, J = 6.0 Hz, 2H), 5.01−5.23 (m, 4H), 5.56−5.62 (m, 2H), 5.71−5.82 (m, 2H), 5.91 (s, 1H), 6.55 (dd, J = 19.6, 6.0 Hz, 1H), 6.92 (s, 1H), 8.63 (brs, 1H), 10.5 (brs, 1H). 13C NMR (CDCl3): 9.7, 9.8, 9.9, 11.5, 13.2, 16.8, 20.2, 21.1, 27.0, 28.6, 31.4, 35.1, 35.6, 46.6, 65.0, 65.2, 97.6, 114.9, 118.0, 118.3, 118.7, 121.1, 122.3, 126.3, 128.2, 130.1, 131.4, 132.0, 132.1, 132.7, 136.6, 137.7, 139.3, 139.6, 140.0, 143.1, 143.4, 148.0, 166.4, 171.5, 171.8, 172.3, 172.5. IR (KBr): 3380, 2920, 1730, 1690, 1650, 1560, 1540, 1500, 1460, 1260, 1020 cm−1. UV−vis (CHCl3): λmax 359 (ε = 70600), 574 (ε = 98400) nm. HRMS−ESI (m/z): Calcd for C43H50N2O6Na [M + Na]+: 741.3628. Found: 741.3655

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.8b01252. Copies of 1H NMR and 13C NMR spectra of products (PDF) Data for C28 H40 N2 O5 (CIF) Data for C28 H39 Cl N2 O5 (CIF) Data for C28 H38 N2 O5 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: ukaji@staff.kanazawa-u.ac.jp. ORCID

Takahiro Soeta: 0000-0001-9883-4772 Yoko Sakata: 0000-0002-6988-1171 Takuya Suga: 0000-0002-7527-9611 Yutaka Ukaji: 0000-0003-3185-3113 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The present work was financially supported in part by the Shibuya Foundation for Academic Culture and Sports, a Grant-in-Aid for Challenging Exploratory Research from JSPS (25620028), Kanazawa University CHOZEN Project, and Kanazawa University SAKIGAKE Project.

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REFERENCES

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DOI: 10.1021/acs.joc.8b01252 J. Org. Chem. 2018, 83, 10743−10748

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DOI: 10.1021/acs.joc.8b01252 J. Org. Chem. 2018, 83, 10743−10748