Polyhydroxylated Quinolizidine Iminosugars as Nanomolar Selective

a potent and selective α-glucosidase inhibitor (Ki = 31 nM).7 This ... ACS Paragon Plus Environment. The Journal of Organic Chemistry. 1. 2. 3. 4. 5...
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Polyhydroxylated Quinolizidine Iminosugars as Nanomolar Selective Inhibitors of α‑Glucosidases Anais Vieira Da Cruz,† Alice Kanazawa,*,† Jean-François Poisson,† Jean-Bernard Behr,‡ and Sandrine Py*,† †

Univ. Grenoble Alpes, DCM and CNRS, DCM, F-38000 Grenoble, France Univ. Reims Champagne-Ardenne, ICMR, CNRS UMR 7312, 51687 Reims Cedex 2, France

‡

S Supporting Information *

ABSTRACT: Polyhydroxylated quinolizidines bearing a hydroxymethyl group at the ring junction were synthesized from a readily available L-sorbose-derived ketonitrone. Evaluated as glycoside hydrolase inhibitors, these quinolizidines revealed to be potent and selective α-glucosidase inhibitors. Quinolizidine 9a is the first quinolizidine-scaffolded iminosugar exhibiting nanomolar inhibition of a glycoenzyme.

I

for such quinolizidines,6 but only compounds 16f and 26g have been described as (modest) glucosidase inhibitors (Figure 1B). Recently, we identified tetrahydroxylated indolizidine 3 (Figure 2) as a potent and selective α-glucosidase inhibitor

minosugars currently constitute the most promising class of glycoprocessing enzyme modulators.1 Due to their structural analogy to the transition state of enzymatic glycoside hydrolysis, they are valuable inhibitors of glycoside hydrolases (glycosidases), with therapeutic applications in the treatment of various disease including diabetes,1,2 viral pathologies,1,3 and lysosomal disorders.1,4 However, glycosidases are ubiquitous enzymes and the identification of inhibitors which would be both potent and highly selective toward a specific subtype is still awaited for tangible progress in drug development. A large number of iminosugars have been evaluated as glycosidase inhibitors, including natural products, such as polyhydroxylated pyrrolidines, piperidines, pyrrolizidines, indolizidines, and nortropanes (Figure 1A).5 To the best of our knowledge, no polyhydroxylated quinolizidine has ever been isolated from nature. The potential activity of these compounds as glycosidase inhibitors has so far been undervalued. A number of syntheses have been reported

Figure 2. Tetrahydroxylated indolizidine 3, a selective α-glucosidase inhibitor compared to CST and DNJ.

(Ki = 31 nM).7 Its excellent selectivity toward α-glucosidases stands out from that of castanospermine (CST) and deoxynojirimycin (DNJ), which also inhibit β-glucosidases.8 The quaternary center at the ring junction of compound 3 probably plays a crucial role for this selectivity and retained potency. Considering that the hydroxylated piperidine ring in 3 mimics the D-glucose 4C1 conformation,9 the second cycle could fit in a cleft that was evolved to accommodate complementary interactions with the aglycone (Figure 2).10 Conversely, the active site of β-glucosidases is not tailored to Figure 1. (A) Common classes of iminosugars. (B) Structural analogies between quinolizidines 1, 2, and a D-glucoside. © 2017 American Chemical Society

Received: June 16, 2017 Published: July 28, 2017 9866

DOI: 10.1021/acs.joc.7b01494 J. Org. Chem. 2017, 82, 9866−9872

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The Journal of Organic Chemistry tolerate steric hindrance on the α-side. A steric clash may thus arise with the five-membered ring of 3, explaining the poor affinity of this inhibitor for β-glucosidases and its high selectivity toward α-glucosidases. With the aim to investigate the structure−activity and structure−selectivity relationship in glycosidase inhibition, we engaged in the synthesis of quinolizidine analogues of 3. As no polyhydroxylated quinolizidine bearing a quaternary center at the ring junction had previously been evaluated against glycosidases, we designed a synthetic route that could lead to several analogues and evaluated their properties as glycosidase inhibitors.11 The synthesis of quinolizidines exhibiting a hydroxymethyl group at C-9a was envisaged from the readily available Lsorbose-derived ketonitrone 4,7 via stereocontrolled nucleophilic C-allylation, N-allylation, and ring-closing metathesis. Nitrone 4 features the appropriate configurations at C-3, C-4, and C-5 positions to mimic the D-glucose substitution pattern at C-4, C-3, and C-2, respectively (Scheme 1).12 This synthetic

Zn(OTf)2, TMSOTf, or Et2AlCl) prior to addition of the organometallic did not increase facial discrimination (Table 1, Entries 2−4, conditions A). However, when the nitrone was added to a solution of premixed ZnCl2 and allylmagnesium bromide (conditions B), the diastereomeric ratio reached 70:30 in favor of 5a (Table 1, Entry 6).17 The two diastereomers were separated by chromatography and their configuration was assigned unambiguously by NOESY experiments. The 2R configuration of the major hydroxylamine 5a was ascertained by NOE cross peak between methylenic protons of the allyl group (δ 2.44−2.56 ppm) and H-4 on the piperidine ring (δ 3.75− 3.80 ppm). In addition, the 2S configuration of the minor hydroxylamine 5b was deduced from NOE cross peak between one methylenic proton of the allyl group (δ 2.42 ppm) and H-3 on the piperidine ring (δ 3.55 ppm). The preferential formation of 5a is explained by axial approach of the organometallic at the electrophilic carbon of nitrone 4 through a chairlike transition state with anti-periplanar relationship between the new developing C−C bond and the nonbonding electronic pair on the nitrogen atom.7 Hydroxylamines 5a and 5b were separately transformed into the corresponding piperidines 7a and 7b by zinc-mediated reduction of the N−O bond, and N-allylation in the presence of allyl bromide (Scheme 2). Satisfyingly, ring-closing metathesis

Scheme 1. Synthetic Approach towards Polyhydroxylated Quinolizidines

Scheme 2. Synthesis of Polyhydroxylated Quinolizidines from 5a and 5b route should allow to access both the products of D-gluco configuration and epimers at C-2 in piperidines or at C-9a in quinolizidines, depending on the selectivity of the nitrone allylation. Allylation of acyclic aldonitrones13 and of five-membered cyclic aldonitrones14 is known to occur with good stereoselectivities. However, only a few examples are reported for sixmembered aldonitrones15 and for ketonitrones.16 Upon addition of allylmagnesium Grignard to a solution of nitrone 4 in dichloromethane at −78 °C, the diastereomeric hydroxylamines 5a and 5b formed in 91% yield, with a diastereomeric ratio of 56:44 (Table 1, Entry 1). Similar results were obtained in THF (83%, d.r. 54:46), toluene (78%, d.r. 52:48), ether (79%, d.r. 53:47), and at 0 °C in CH2Cl2 (61%, d.r. 54:46). Precomplexation of nitrone 4 with various Lewis acids (ZnCl2, Table 1. C-Allylation of Ketonitrone 4

entry

AllylMgBr (equiv)

1 2 3

2 3.6 3.6

4 5 6

2.4 2.4 3.6

Lewis acid (equiv) ZnCl2 (1.2)a Zn(OTf)2 (1.2)a TMSOTf (1.1)a Et2AlCl (1.2)a ZnCl2 (1.2)b

time (h)

d.r. (5a/5b)

yield (%)

0.5 3.5 5

56:44 65:35 50:50

91 86 83

1.5 3.5 3.5

55:46 66:34 70:30

66 100 77c

of compounds 7a and 7b using Grubbs’ II catalyst very efficiently yielded the bicyclic products 8a and 8b in 95% and 81% yields, respectively (Scheme 2).18 The basic nitrogen did not interfere with the cyclization, surely thanks to steric hindrance of this α-quaternary amine, preventing the ruthenium catalysis deactivation. The combined hydrogenation of the double bond and debenzylation in the presence of Pearlman’s catalyst (Pd(OH)2/C), under pressure of hydrogen afforded the tetrahydroxylated quinolizidines 9a and 9b. Quinolizidines 10a and 10b with two additional hydroxyl groups were next synthesized by dihydroxylation of the major intermediate 8a.19 From 8a two diastereomeric products 10a and 10b (formed in a 60:40 ratio) were isolated in 43% and 26% yield, respectively. The relative configuration of the newly

a

Precomplexation of the Lewis acid with the nitrone (conditions A). Precomplexation of the Lewis acid with the organometallic (conditions B). cNitrone 4 (18%) was recovered.

b

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DOI: 10.1021/acs.joc.7b01494 J. Org. Chem. 2017, 82, 9866−9872

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The Journal of Organic Chemistry

mechanisms of interaction of these potent inhibitors with αglucosidases, and understand the features associated with their outstanding selectivity.

formed stereogenic centers of both isomers was determined by NOESY correlations. The osmylation occurred preferentially from the least hindered face of the olefin, opposite to the ring junction benzyloxymethyl substituent (Scheme 2). Finally, the iminosugars 11a and 11b were obtained quantitatively by hydrogenolysis of the benzyl protecting groups. The inhibitory activity of compounds 9a, 9b, 11a, and 11b, was evaluated on a panel of commercially available glycosidases.20 Satisfyingly, all D-gluco configurated quinolizidines (9a, 11a, 11b) were found to be potent and selective inhibitors of α-glucosidases (Table 2). The hydrolytic activity

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General Methods. All the reactions were performed under argon pressure and magnetic stirring, in glassware previously dried in a oven. The standard handling techniques under an inert atmosphere were used for sensitive air and moisture reagents. Dichloromethane and acetonitrile were distilled over CaH2. THF, toluene, and ether were distilled over sodium (in the presence of benzophenone for ethers). The reactions were monitored by thin layer chromatography (TLC) using commercial aluminum-backed silica gel plates (Merck, Kieselgel 60 F254). TLC spots were viewed under ultraviolet light and by heating the plate after treatment with 3% solution of potassium permanganate in 10% aqueous potassium hydroxide (w/v). Product purifications by gravity column chromatography were performed using Macherey−Nagel silica gel 60 (70−230 mesh). Optical rotations were measured on a PerkinElmer 341 polarimeter. Infrared spectra were obtained from neat compounds, on a Nicolet “Magna 550” spectrometer using an ATR (attenuated total reflection) module. The data are reported in reciprocal centimeters (cm−1). 1H NMR and 13 C NMR (DEPTQ-135) spectra were recorded on a Bruker Avance 500 (1H: 500 MHz, 13C: 125 MHz) spectrometer. Chemical shifts for 1 H spectra are values from tetramethylsilane in CDCl3 (δ 0.00 ppm), toluene-d8 (δ 2.08 ppm), or CD3OD (δ 3.31 ppm). Chemical shifts for 13 C spectra are values from CDCl3 (δ 77.16 ppm), toluene-d8 (δ 20.43 ppm), or CD3OD (δ 49.00 ppm). 1H NMR spectra are reported as following: chemical shift (ppm), multiplicity (br: broad; s: singlet; d: doublet; dd: doublet of doublets; t: triplet; pt: pseudo triplet; m: multiplet), coupling constants (Hz), and integration. Proton and carbon signal assignments were established using COSY, HSQC, and HMBC experiments. High-resolution mass spectra (HRMS) were recorded on a Waters G2-S Q-TOF mass spectrometer. U-HPLC analysis of final compounds (9a, 9b, 11a, and 11b) was performed on a Thermo Scientific Dionex Ultimate 3000 apparatus equipped with a Varian 380-LC DEDL detector (see Supporting Information). General Procedure for C-Allylation of Nitrone 4. Allylmagnesium bromide (1 M solution in ether, 2.4 mL, 2.4 mmol) and ZnCl2 (1 M solution in ether, 2.4 mL, 2.4 mmol) were mixed in a Schlenk tube. The solution was stirred at room temperature during 20 min, then cooled at −78 °C. A solution of nitrone 4 (1.025 g, 1.9 mmol) in dry CH2Cl2 (15 mL) was then added dropwise at −78 °C to the first solution. After 1 h 30, TLC analysis showed uncomplete reaction, thus allylmagnesium bromide (4.8 mL, 4.8 mmol) was added to the reaction mixture. After 1 h 50 a saturated aqueous solution of NH4Cl was added and the aqueous phase was extracted three times with dichloromethane. The organic layers were washed with brine, dried over MgSO4, filtered, and concentrated under vacuum to afford a mixture of the two diastereoisomeric hydroxylamines 5a and 5b (5a/ 5b = 70:30). Upon chromatography on silica gel (pentane/ether 90:10, 85:15 and 80:20), the major hydroxylamine 5a (colorless oil, 646 mg, 58%) was separated from hydroxylamine 5b (colorless oil, 209 mg, 19%) and from recovered starting material 4 (191 mg, 18%). (2R,3R,4R,5S)-2-Allyl-3,4,5-tris(benzyloxy)-2((benzyloxy)methyl)piperidin-1-ol (5a). [α]20D −19 (c 0.96, CHCl3); IR ν 3361 (m), 3088 (m), 3063 (m), 3030 (m), 2922 (s), 2863 (s), 1496 (m), 1453 (m); 1 H NMR (500 MHz, CDCl3) δ 2.44−2.56 (m, 2H, 7CH2), 3.01 (pt, J = 11.5 Hz, 1H, 6CH2), 3.44 (dd, J = 5.3, 12.0 Hz, 1H, 6CH2), 3.57 (d, J = 9.5 Hz, 1H, 10CH2), 3.70 (d, J = 9.5 Hz, 1H, 10CH2), 3.75−3.80 (m, 1H, 4CH), 3.84−3.91 (m, 2H, 3CH, 5H), 4.41 (d, J = 11.8 Hz, 1H, Bn CH2), 4.47 (d, J = 11.0 Hz, 1H, BnCH2), 4.51 (d, J = 12.0 Hz, 1H, Bn CH2), 4.65 (d, J = 11.5 Hz, 1H, BnCH2), 4.70 (d, J = 11.5 Hz, 1H, Bn CH2), 4.78 (d, J = 11.0 Hz, 1H, BnCH2), 4.86 (d, J = 11.0 Hz, 1H, Bn CH2), 4.90 (d, J = 11.0 Hz, 1H, BnCH2), 4.95−5.04 (m, 2H, 9CH2), 5.57 (br s, 1H, OH), 5.93−6.03 (m, 1H, 8CH), 7.15−7.19 (m, 2H, Ar CH), 7.23−7.32 (m, 18H, ArCH) ppm; 13C NMR (125 MHz, CDCl3) δ 32.0 (7CH2), 53.9 (6CH2), 67.5 (2Cq), 71.3 (10CH2), 73.3

Table 2. Inhibitory Activity against Glycosidasesa,b enzyme

9a

9b

11a

11b

DNJ

α-glucosidase (rice) [IC50] α-glucosidase (S. cerevisiae) [IC50] β-glucosidase (almond) β-glucosidase (A. niger) β-galactosidase (A. orizae) α-mannosidase (Jack bean) α-rhamnosidase (A. niger)

97% [0.047]c 97%

98% [107] 89%

100% [0.26] 5%

100% [0.79] 11%

100% [0.035]d 74%

[300] NI

n.d. 26%

n.d. NI

n.d NI

[23]e 93%

10%

10%

NI

16%

98%

7%

11%

NI

NI

n.d.

NI

NI

NI

NI

n.d.

11%

8%

NI

NI

n.d.

EXPERIMENTAL SECTION

a

Expressed as % inhibition at 1 mM concentration of inhibitor, IC50 in μM. bNI means no inhibition; n.d. means not determined. cMixed inhibition, Ki = 0.057 μM, Ki′ = 0.361 μM. dLit.21 IC50 = 0.036 μM, Ki = 0.066 μM, competitive. eTaken from ref 21; Ki = 22 μM.21

of all other tested enzymes (β-glucosidases, β-galactosidase, βmannosidase, β-rhamnosidase) was almost unaffected by the evaluated quinolizidines. Compound 9a, which can be viewed as a homologue of indolizidine 3 or castanospermine, was the most active inhibitor of rice α-glucosidase (IC50 = 47 nM), comparing very well with the standard DNJ (IC50 = 35 nM) tested here under the same conditions. It also inhibits αglucosidase from S. cerevisiae, albeit to a much lower extent (IC50 = 300 μM). Unsurprisingly, quinolizidine 9b (epimer at C-9a), which features a L-ido configuration for the polyhydroxylated ring, was significantly less potent (IC50 = 107 μM toward rice α-glucosidase). Interestingly, hexahydroxylated quinolizidines 11a and 11b are also effective inhibitors of rice α-glucosidase (IC50 = 0.26 and 0.79 μM, respectively), but their affinity for the active site is markedly decreased compared to that of 9a. This might be due to less favorable interactions of the additional dihydroxylated cycle when compared to the unsubstituted one. This effect is heightened regarding αglucosidase from yeast, the inhibition of which is wiped out by the presence of the additional hydroxyl groups. As revealed by Lineweaver−Burk plots (see SI), 9a is a mixed inhibitor of rice α-glucosidase (Ki = 57 nM, Ki′ = 361 nM), with a slow-tight binding. In conclusion, using a short and efficient synthetic route, polyhydroxylated quinolizidines bearing a hydroxymethyl substituent at the ring junction were prepared and assessed as glycosidase inhibitors. The latter, and in particular compound 9a, which exhibits similar profile as indolizidine 3, proved to be exceptionally potent and selective inhibitors of α-glucosidases. Further studies are currently underway to elucidate the 9868

DOI: 10.1021/acs.joc.7b01494 J. Org. Chem. 2017, 82, 9866−9872

Note

The Journal of Organic Chemistry (BnCH2), 73.7 (BnCH2), 75.6 (BnCH2), 77.1 (5CH), 78.8 (3CH), 83.6 (4CH), 117.0 (9CH2), 127.4 (ArCH), 127.5 (ArCH), 127.7 (ArCH), 127.9 (ArCH), 127.9 (ArCH), 128.0 (ArCH), 128.0 (ArCH), 128.2 (ArCH), 128.3 (ArCH), 128.5 (ArCH), 128.6 (ArCH), 134.8 (8CH), 137.7 (ArCq), 138.4 (ArCq), 138.9 (ArCq), 139.0 (ArCq) ppm; HRMS (ESI) Calcd for C37H42NO5: m/z = 580.3063 [M+H]+, Found m/z = 580.3057. NOESY correlation between 7H (δ 2.44−2.56 ppm) and 4H (δ 3.75−3.80 ppm). (2S,3R,4R,5S)-2-Allyl-3,4,5-tris(benzyloxy)-2-((benzyloxy)methyl)piperidin-1-ol (5b). [α]20D −15 (c 1.39, CHCl3); IR ν 3391 (br), 3088 (w), 3063 (m), 3030 (m), 2919 (s), 2861 (s),1496 (m), 1453 (m) cm−1; 1H NMR (500 MHz, CDCl3) δ 2.42 (dd, J = 8.5, 14.0 Hz, 1H, 7 CH2), 2.88−3.00 (m, 1H, 7CH2), 3.18 (t, J = 10.5 Hz, 1H, 6CH2), 3.55 (br d, J = 7.5 Hz, 1H, 3CH), 3.61 (dd, J = 5.5, 10.5 Hz, 1H, 6 CH2), 3.69−3.80 (m, 2H, 5CH, 10CH2), 3.85 (t, J = 9.0 Hz, 1H, 4 CH), 4.09−4.18 (m, 1H, 10CH2), 4.53 (s, 2H, BnCH2), 4.65 (d, J = 11.5 Hz, 1H, BnCH2), 4.66 (s, 2H, BnCH2), 4.70 (d, J = 11.0 Hz, 1H, Bn CH2), 4.91 (d, J = 11.0 Hz, 1H, BnCH2), 4.92 (d, J = 11.0 Hz, 1H, Bn CH2), 5.05−5.13 (m, 2H, 9CH2), 5.98−6.08 (m, 1H, 8CH), 6.32 (br s, 1H, OH), 7.19−7.38 (m, 20H, ArCH) ppm; 13C NMR (125 MHz, CDCl3) δ 35.6 (7CH2), 55.2 (6CH2), 67.2 (2Cq), 71.3 (10CH2), 72.8 (BnCH2), 74.3 (BnCH2), 75.6 (BnCH2), 75.6 (BnCH2), 77.4 (5CH), 79.9 (3CH), 84.1 (4CH), 117.9 (9CH2), 127.3 (ArCH), 127.6 (ArCH), 127.7 (ArCH), 127.8 (ArCH), 127.9 (ArCH), 128.0 (ArCH), 128.0 (ArCH), 128.1 (ArCH), 128.5 (ArCH), 128.5 (ArCH), 128.6 (ArCH), 128.7 (ArCH), 134.8 (8CH), 137.5 (ArCq), 138.4 (ArCq), 138.8 (ArCq), 138.9 (ArCq) ppm; HRMS (ESI) Calcd for C37H42NO5: m/z = 580.3063 [M +H]+, Found m/z = 580.3056. NOESY correlation between 7H (δ 2.42 ppm) and 3H (δ 3.55 ppm). (2R,3R,4R,5S)-2-Allyl-3,4, 5-tris(benzyloxy)-2((benzyloxy)methyl)piperidine (6a). Hydroxylamine 5a (646 mg, 1.11 mmol) was dissolved in a 4:1 mixture of ethanol/acetic acid (28 mL), then zinc dust (1.5 g, 23 mmol) was added. The suspension was placed in an ultrasound bath at 80 °C for 1 h. A solution of 10% NaOH was added and the aqueous phase was extracted three times with dichloromethane. The organic layers were washed with brine, dried over MgSO4, filtered, and then concentrated under vacuum. After purification by chromatography on silica gel (pentane/AcOEt 7:3, then 5:5), the piperidine 6a was obtained as a colorless oil (604 mg, 96%). [α]20D +27 (c 1.47, CHCl3); IR ν 3333 (w), 3088 (w), 3064 (m), 3030 (m), 2923 (s), 2856 (s),1496 (m), 1453 (m) cm−1; 1H NMR (500 MHz, CDCl3) δ 2.29 (dd, J = 7.5, 15.0 Hz, 1H, 7CH2), 2.50 (dd, J = 7.0, 15.0 Hz, 1H, 7CH2), 2.64 (dd, J = 11.0, 13.5 Hz, 1H, 6 CH2), 3.06 (dd, J = 5.5, 13.5 Hz, 1H, 6CH2), 3.34 (d, J = 9.0 Hz, 1H, 10 CH2), 3.43−3.49 (m, 1H, 5CH), 3.52 (d, J = 9.0 Hz, 1H, 10CH2), 3.71 (d, J = 9.5 Hz, 1H, 3CH), 3.77 (t, J = 9.5 Hz, 1H, 4CH), 4.33 (d, J = 11.5 Hz, 1H, BnCH2), 4.45 (d, J = 11.5 Hz, 1H, BnCH2), 4.48 (d, J = 11.5 Hz, 1H, BnCH2), 4.66 (d, J = 11.5 Hz, 1H, BnCH2), 4.71 (d, J = 11.5 Hz, 1H, BnCH2), 4.80 (d, J = 10.5 Hz, 1H, BnCH2), 4.87 (d, J = 11.5 Hz, 1H, BnCH2), 4.93 (d, J = 10.5 Hz, 1H, BnCH2), 5.04−5.10 (m, 2H, 9CH2), 5.80−5.90 (m, 1H, 8CH), 7.19−7.35 (m, 20H, ArCH) ppm; 13C NMR (125 MHz, CDCl3) δ 32.6 (7CH2), 43.1 (6CH2), 59.8 (2Cq), 72.7 (10CH2), 73.1 (BnCH2), 73.4 (BnCH2), 75.5 (BnCH2), 75.9 (BnCH2), 81.4 (3CH), 82.1 (5CH), 84.1 (4CH), 117.8 (9CH2), 127.5 (ArCH), 127.6 (ArCH), 127.7 (ArCH), 127.8 (ArCH), 127.9 (ArCH), 127.9 (ArCH), 128.0 (ArCH), 128.1 (ArCH), 128.4 (ArCH), 128.5 (ArCH), 128.5 (ArCH), 128.6 (ArCH), 133.6 (8CH), 138.1 (ArCq), 138.7 (ArCq), 139.0 (ArCq), 139.2 (ArCq) ppm; HRMS (ESI) Calcd for C37H42NO4: m/z = 564.3114 [M+H]+, Found m/z = 564.3118. NOESY correlation between 7H (δ 2.50 ppm) and 4H (δ 3.77 ppm). (2S,3R,4R,5S)-2-Allyl-3,4,5-tris(benzyloxy)-2-((benzyloxy)methyl)piperidine (6b). Hydroxylamine 5b (364 mg, 0.63 mmol) was dissolved in a 4:1 mixture of ethanol/acetic acid (16 mL), then zinc dust (0.90 g, 13 mmol) was added. The suspension was placed in an ultrasound bath at 80 °C for 1 h. A solution of 10% NaOH was added and the aqueous phase was extracted three times with dichloromethane. The organic layers were washed with brine, dried over MgSO4, filtered, and then concentrated under vacuum. After purification by chromatography on silica gel (pentane/AcOEt 7:3

then 5:5), the piperidine 6b was obtained as a colorless oil (283 mg, 81%). [α]20D −23 (c 1.49, CHCl3); IR ν 3338 (w), 3091 (w), 3064 (m), 3030 (m), 2916 (s), 2853 (s), 1496 (m), 1453 (m) cm−1; 1H NMR (500 MHz, CDCl3) δ 2.35 (dd, J = 8.0, 14.5 Hz, 1H, 7CH2), 2.53 (dd, J = 6.5, 14.5 Hz, 1H, 7CH2), 2.69 (pt, J = 11.5 Hz, 1H, 6 CH2), 3.09 (dd, J = 5.5, 12.0 Hz, 1H, 6CH2), 3.46 (d, J = 9.5 Hz, 2H, 10 CH2, 3CH), 3.52−3.58 (m, 1H, 5CH), 3.73 (t, J = 9.0 Hz, 1H, 4CH), 3.89 (d, J = 10.0 Hz, 1H, 10CH2), 4.52 (d, J = 12.0 Hz, 1H, BnCH2), 4.56 (d, J = 12.0 Hz, 1H, BnCH2), 4.62−4.69 (m, 3H, BnCH2), 4.72 (d, J = 11.0 Hz, 1H, BnCH2), 4.91 (d, J = 11.0 Hz, 1H, BnCH2), 4.93 (d, J = 10.5 Hz, 1H, BnCH2), 5.02−5.09 (m, 2H, 9CH2), 5.86−5.95 (m, 1H, 8 CH), 7.21−7.38 (m, 20H, ArCH) ppm; 13C NMR (125 MHz, CDCl3) δ 40.8 (7CH2), 43.6 (6CH2), 60.3 (2Cq), 68.8 (10CH2), 72.8 (BnCH2), 73.7 (BnCH2), 75.5 (BnCH2), 75.7 (BnCH2), 81.0 (5CH), 82.5 (3CH), 84.7 (4CH), 118.2 (9CH2), 127.4 (ArCH), 127.5 (ArCH), 127.7 (ArCH), 127.7 (ArCH), 127.8 (ArCH), 127.8 (ArCH), 127.9 (ArCH), 128.1 (ArCH), 128.4 (ArCH), 128.5 (ArCH), 128.5 (ArCH), 128.6 (ArCH), 134.4 (8CH), 138.6 (ArCq), 138.7 (ArCq), 139.0 (ArCq), 139.1 (ArCq) ppm; HRMS (ESI) Calcd for C37H42NO4: m/z = 564.3114 [M +H]+, Found m/z = 564.3118. NOESY correlation between 4H (δ 3.73 ppm) and 10H (δ 3.89 ppm). (2R,3R,4R,5S)-1,2-Diallyl-3,4,5-tris(benzyloxy)-2-((benzyloxymethyl)-piperidine (7a). To a solution of amine 6a (481 mg, 0.85 mmol) in dry CH3CN (50 mL) was added potassium carbonate (768 mg, 5,55 mmol), potassium iodide (14 mg, 0.08 mmol), and allyl bromide (350 μL, 4.10 mmol). The solution was stirred at 82 °C, during 17 h. A saturated solution of sodium hydrogenocarbonate was added and the aqueous phase was extracted three times with dichloromethane. The organic layers were dried over MgSO4, filtered, and concentrated under vacuum. After purification by chromatography on silica gel (pentane, pentane/AcOEt 95:5, then pentane/AcOEt 50:50), the N-allylpiperidine 7a was obtained as a colorless oil (468 mg, 90%). [α]20D +25 (c 1.00, CHCl3); IR ν 3091 (w), 3064 (m), 3029 (m), 2908 (s), 2862 (s), 1638 (w), 1496 (m), 1453 (m) cm−1; 1 H NMR (500 MHz, CDCl3) δ 2.29 (dd, J = 7.0, 14.5 Hz, 1H, 7CH2), 2.36−2.47 (m, 2H, 6CH2, 7CH2), 2.86 (dd, J = 7.5, 14.0 Hz, 1H, 11 CH2), 3.00 (dd, J = 5.5, 12.0 Hz, 1H, 6CH2), 3.37 (br d, J = 14.0 Hz, 1H, 11CH2), 3.43 (d, J = 10.5 Hz, 1H, 10CH2), 3.46 (d, J = 10.5 Hz, 1H, 10CH2), 3.51−3.57 (m, 1H, 5CH), 3.68 (t, J = 9.0 Hz, 1H, 4CH), 3.73 (d, J = 9.5 Hz, 1H, 3CH), 4.31 (d, J = 12.0 Hz, 1H, BnCH2), 4.36 (d, J = 12.0 Hz, 1H, BnCH2), 4.42 (d, J = 11.5 Hz, 1H, BnCH2), 4.55 (d, J = 11.5 Hz, 1H, BnCH2), 4.59 (d, J = 11.5 Hz, 1H, BnCH2), 4.70 (d, J = 11.0 Hz, 1H, BnCH2), 4.81 (d, J = 10.5 Hz, 1H, BnCH2), 4.83 (d, J = 11.0 Hz, 1H, BnCH2), 4.85−5.05 (m, 4H, 9CH2, 13CH2), 5.63− 5.73 (m, 1H, 12CH), 5.76−5.85 (m, 1H, 8CH), 7.08−7.25 (m, 20H, Ar CH) ppm; 13C NMR (125 MHz, CDCl3) δ 31.9 (7CH2), 48.0 6 ( CH2), 52.7 (11CH2), 63.7 (2Cq), 69.8 (10CH2), 72.9 (BnCH2), 73.3 (BnCH2), 75.4 (BnCH2), 75.5 (BnCH2), 79.2 (5CH), 80.9 (3CH), 84.2 (4CH), 116.3 (13CH2), 117.2 (9CH2), 127.3 (ArCH), 127.3 (ArCH), 127.4 (ArCH), 127.7 (ArCH), 127.9 (ArCH), 127.9 (ArCH), 128.0 (ArCH), 128.3 (ArCH), 128.3 (ArCH), 128.4 (ArCH), 128.5 (ArCH), 135.1 (8CH), 137.5 (12CH), 138.1 (ArCq), 138.7 (ArCq), 139.3 (ArCq), 139.4 (ArCq) ppm; HRMS (ESI) Calcd for C40H46NO4: m/z = 604.3427 [M+H]+, Found m/z = 604.3427. NOESY correlation between 7H (δ 2.29 ppm) and 4H (δ 3.68 ppm). (2S,3R,4R,5S)-1,2-Diallyl-3,4,5-tris(benzyloxy)-2-(benzyloxy-methyl)-piperidine (7b). To a solution of amine 6b (182 mg, 0.32 mmol) in dry CH3CN (20 mL) was added potassium carbonate (300 mg, 2.2 mmol), potassium iodide (11 mg, 0.1 mmol), and allyl bromide (140 μL, 1.5 mmol). The solution was stirred at 80 °C, during 13 h. A saturated solution of sodium hydrogenocarbonate was added and the aqueous phase was extracted three times with dichloromethane. The organic layers were dried over MgSO4, filtered, and concentrated under vacuum. After purification by chromatography on silica gel (pentane, pentane/AcOEt 95:5), the N-allylpiperidine 7b was obtained as a colorless oil (163 mg, 83%). [α]20D −17 (c 1.05, CHCl3); IR ν 3085 (w), 3064 (m), 3029 (m), 2905 (s), 2858 (s), 1639 (w), 1605 (w), 1496 (m), 1453 (m) cm−1; 1H NMR (500 MHz, CDCl3) δ 2.31 (dd, J = 8.5, 16.0 Hz, 1H, 7CH2), 2.53 (pt, J = 11.5 Hz, 9869

DOI: 10.1021/acs.joc.7b01494 J. Org. Chem. 2017, 82, 9866−9872

Note

The Journal of Organic Chemistry 1H, 6CH2), 2.66 (br d, J = 16.0 Hz, 1H, 7CH2), 2.84 (dd, J = 7.5, 15.0 Hz, 1H, 11CH2), 3.01 (dd, J = 5.5, 11.5 Hz, 1H, 6CH2), 3.38−3.47 (m, 3H, 10CH2, 3CH, 5CH), 3.57 (br d, J = 15.0 Hz, 1H, 11CH2), 3.78 (t, J = 9.5 Hz, 1H, 4CH), 3.88 (d, J = 10.0 Hz, 1H, 10CH2), 4.43 (s, 2H, Bn CH2),, 4.55−4.61 (m, 3H, BnCH2), 4.65 (d, J = 11.0 Hz, 1H, BnCH2), 4.84 (d, J = 11.0 Hz, 1H, BnCH2), 4.90 (d, J = 11.5 Hz, 1H, BnCH2), 4.92−5.08 (m, 4H, 9CH2, 13CH2), 5.57−5.67 (m, 1H, 12CH), 5.73− 5.83 (m, 1H, 8CH), 7.13−7.29 (m, 20H, ArCH) ppm; 13C NMR (125 MHz, CDCl3) δ 35.2 (7CH2), 48.8 (6CH2), 52.6 (11CH2), 64.6 (2Cq), 69.4 (10CH2), 72.7 (BnCH2), 73.6 (BnCH2), 75.3 (BnCH2), 75.5 (BnCH2), 79.7 (5CH), 81.4 (3CH), 84.5 (4CH), 115.8 (13CH2), 117.9 (9CH2), 127.1 (ArCH), 127.4 (ArCH), 127.4 (ArCH), 127.5 (ArCH), 127.6 (ArCH), 127.7 (ArCH), 127.9 (ArCH), 128.1 (ArCH), 128.4 (ArCH), 128.4 (ArCH), 128.5 (ArCH), 134.4 (8CH), 137.6 (12CH), 138.8 (ArCq), 138.9 (ArCq), 139.1 (ArCq), 139.4 (ArCq) ppm; HRMS (ESI) Calcd for C40H46NO4: m/z = 604.3427 [M+H]+, Found m/z = 604.3434. (1R,2R,3S,9aR)-1,2,3-Tris(benzyloxy)-9a-((benzyloxy)methyl)2,3,4,6,9−9a-hexahydro-1H-quinolizine (8a). To a solution of Nallylpiperidine 7a (35 mg, 0.06 mmol) in degazed dichloromethane (3 mL) was added second generation Grubbs’ catalyst (1.3 mg, 2.5 mol %). The solution was stirred at room temperature during 20 h. The reaction mixture was then filtered on a plug of silica gel (rinsed with AcOEt and methanol), and concentrated under vacuum. After purification by chromatography on silica gel (pentane/AcOEt 9:1, then 7:3), compound 8a was obtained as a brown oil (32 mg, 95%). [α]20D +9 (c 0.35, CHCl3); IR ν 3063 (m), 3028 (m), 2901 (s), 2853 (s), 1496 (w), 1453 (m), 1362 (w), 1088 (s) cm−1; 1H NMR (500 MHz, CDCl3) δ 1.49−1.71 (m, 1H, 9CH2), 2.32 (d, J = 19.0 Hz, 1H, 9 CH2), 2.80 (t, J = 10.5 Hz, 1H, 4CH2), 2.89−3.05 (m, 2H, 4CH2, 6 CH2), 3.42 (d, J = 10.0 Hz, 1H, 10CH2), 3.50 (d, J = 10.0 Hz, 1H, 10 CH2), 3.65−3.83 (m, 4H, 1CH, 2CH, 3CH, 6CH2), 4.23 (d, J = 11.5 Hz, 1H, BnCH2), 4.42 (d, J = 12.5 Hz, 1H, BnCH2), 4.57 (d, J = 12.5 Hz, 1H, BnCH2), 4.66 (d, J = 11.5 Hz, 1H, BnCH2), 4.70 (d, J = 11.5 Hz, 1H, BnCH2), 4.75 (d, J = 11.0 Hz, 1H, BnCH2), 4.85 (d, J = 11.5 Hz, 1H, BnCH2), 4.94 (d, J = 11.0 Hz, 1H, BnCH2), 5.56−5.68 (m, 2H, 7 CH, 8CH), 7.07 (d, J = 6.6 Hz, 2H, ArCH), 7.17−7.35 (m, 18H, Ar CH) ppm; 13C NMR (125 MHz, CDCl3) δ 21.6 (9CH2), 49.0 6 ( CH2), 52.1 (4CH2), 60.0 (9aCq), 68.5 (10CH2), 72.8 (BnCH2), 73.7 (BnCH2), 75.4 (BnCH2), 75.6 (BnCH2), 79.2 (3CH), 79.9 (1CH), 84.4 (2CH), 123.6 (8CH), 124.1 (7CH), 127.3 (ArCH), 127.4 (ArCH), 127.6 (ArCH), 127.7 (ArCH), 127.9 (ArCH), 128.0 (ArCH), 128.1 (ArCH), 128.2 (ArCH), 128.4 (ArCH), 128.5 (ArCH), 128.5 (ArCH), 128.7 (ArCH), 137.9 (ArCq), 138.7 (ArCq), 139.1 (ArCq), 139.2 (ArCq) ppm; HRMS (ESI) Calcd for C38H42NO4: m/z = 576.3114 [M+H]+, Found m/z = 576.3110. (1R,2R,3S,9aS)-1,2,3-Tris(benzyloxy)-9a-((benzyloxy)methyl)2,3,4,6,9,9a-hexahydro-1H-quinolizine (8b). To a solution of Nallylpiperidine 7b (29 mg, 0.05 mmol) in degazed dichloromethane (2 mL) was added second generation Grubbs’ catalyst (6.9 mg, 15 mol %). The solution was stirred at room temperature during 41 h. The reaction mixture was then filtered on a plug of silica gel (rinsed with AcOEt and methanol), and concentrated under vacuum. After purification by chromatography on silica gel (pentane/AcOEt 9:1 then 7:3), compound 8b was obtained as a brown oil (22 mg, 81%). [α]20D −7 (c 1.25, CHCl3); IR ν 3063 (m), 3030 (m), 2911 (s), 2863 (s), 1497 (w), 1453 (m), 1369 (w), 1088 (s) cm−1; 1H NMR (500 MHz, CDCl3) δ 1.97 (br d, J = 18.0 Hz, 1H, 9CH2), 2.10 (br d, J = 17.5 Hz, 1H, 9CH2), 2.93 (dd, J = 6.0, 10.5 Hz, 1H, 4CH2), 3.13 (d, J = 17.0 Hz, 1H, 6CH2), 3.24−3.38 (m, 3H, 1CH, 4CH2, 6CH2), 3.71− 3.77 (m, 1H, 3CH), 3.79 (d, J = 10.0 Hz, 1H, 10CH2), 3.84 (d, J = 10.0 Hz, 1H, 10CH2), 4.33 (t, J = 9.5 Hz, 1H, 2CH), 4.48 (d, J = 12.5 Hz, 1H, BnCH2), 4.52 (d, J = 12.5 Hz, 1H, BnCH2), 4.64 (d, J = 11.5 Hz, 1H, BnCH2), 4.68 (d, J = 11.5 Hz, 1H, BnCH2), 4.72 (d, J = 11.5 Hz, 1H, BnCH2), 4.81 (d, J = 11.0 Hz, 1H, BnCH2), 4.91 (d, J = 11.0 Hz, 1H, BnCH2), 5.04 (d, J = 11.5 Hz, 1H, BnCH2), 5.57−5.67 (m, 2H, 7 CH, 8CH), 7.21−7.37 (m, 20H, ArCH) ppm; 13C NMR (125 MHz, CDCl3) δ 35.4 (9CH2), 49.9 (6CH2), 54.0 (4CH2), 59.7 (9aCq), 69.1 (10CH2), 72.8 (BnCH2), 73.5 (BnCH2), 75.4 (BnCH2), 76.1 (BnCH2),

79.2 (3CH), 83.8 (2CH), 87.5 (1CH), 123.6 (8CH), 124.5 (7CH), 127.4 (ArCH), 127.4 (ArCH), 127.4 (ArCH), 127.5 (ArCH), 127.6 (ArCH), 127.8 (ArCH), 128.3 (ArCH), 128.3 (ArCH), 128.4 (ArCH), 128.4 (ArCH), 138.7 (ArCq), 139.1 (ArCq), 139.2 (ArCq), 139.2 (ArCq) ppm; HRMS (ESI) Calcd for C38H42NO4: m/z = 576.3114 [M+H]+, Found m/z = 576.3120. (1R,2R,3S,9aR)-9a-(Hydroxymethyl)octahydro-1H-quinolizine1,2,3-triol (9a). To a solution of 8a (34 mg, 0.06 mmol) in methanol (1 mL) was added 20% Pd(OH)2/C (14 mg, 0.10 mmol) and HCl (2 M in Et2O, 45 μL, 0.09 mmol). The suspension was stirred overnight under hydrogen (5 bar) then filtered over Celite. The Celite was rinsed with methanol and the filtrate was concentrated under vacuum. The residue was purified through a column of DOWEX 50W-X8 ion -exchange resine, eluting with water and NH4OH (1 N). The tetrahydroxylated quinolizidine 9a was obtained as a colorless oil (9 mg, 73%). [α]20D +17 (c 0.41, MeOH); IR ν 3336 (s), 2942 (m), 2869 (m), 1053 (m) cm−1; 1H NMR (500 MHz, CD3OD, presat HOD) δ 1.28 (br d, J = 11.6 Hz, 1H, 7CH2), 1.37−1.44 (m, 1H, 9CH2), 1.62− 1.76 (m, 3H, 8CH2, 9CH2), 1.81−1.94 (m, 1H, 7CH2), 2.66 (dd, J = 3.0, 14.0 Hz, 1H, 6CH2), 2.72 (dd, J = 4.9, 11.3 Hz, 1H, 4CH2), 3.12 (t, J = 11.0 Hz, 1H, 4CH2), 3.20 (td, J = 3.0, 14.0 Hz, 1H, 6CH2), 3.38 (t, J = 9.3 Hz, 1H, 2CH), 3.45−3.52 (m, 2H, 1CH, 3CH), 3.68 (d, J = 11.1 Hz, 1H, 10CH2), 3.95 (d, J = 11.1 Hz, 1H, 10CH2) ppm; 13C NMR (125 MHz, CD3OD) δ 18.7 (7CH2), 19.2 (9CH2), 20.7 (8CH2), 48.5 (6CH2), 53.3 (4CH2), 60.7 (10CH2), 62.0 (9aCq), 71.4 (3CH), 74.1 (1CH), 75.9 (2CH) ppm; HRMS (ESI) Calcd for C10H20NO4: m/z = 218.1392 [M+H]+, Found m/z = 218.1396. NOESY correlation between 10H (δ 3.68 and 3.95 ppm) and 1H/3H (δ 3.45−3.52 ppm). (1R,2R,3S,9aS)-9a-(Hydroxymethyl)octahydro-1H-quinolizine1,2,3-triol (9b). To a solution of 8b (25 mg, 0.04 mmol) in methanol (1 mL) was added 20% Pd(OH)2/C (14 mg, 0.10 mmol) and HCl (2 M in Et2O, 35 μL, 0.07 mmol). The suspension was stirred overnight under hydrogen (5 bar) then filtered over Celite. The Celite was rinsed with methanol and the filtrate was concentrated under vacuum. The residue was purified through a column of DOWEX 50W-X8 ion exchange resine, eluting with water and NH4OH (1 N). The tetrahydroxylated quinolizidine 9b was obtained as a colorless oil (7.7 mg, 81%). [α]20D +27 (c 0.38, MeOH); IR ν 3304 (s), 2927 (m), 2851 (m), 1653 (w), 1453 (w), 1099 (m), 1040 (m), 1004 (m) cm−1; 1 H NMR (500 MHz, CD3OD, presat HOD) δ 1.40−1.51 (m, 1H, 9 CH2), 1.56−1.71 (m, 4H, 7CH2, 8CH2), 2.17 (td, J = 5.0, 13.5 Hz, 1H, 9 CH2), 2.68−2.77 (m, 1H, 6CH2), 2.77−2.92 (m, 3H, 4CH2, 6CH2), 3.40 (br d, J = 6.7 Hz, 1H, 1CH), 3.63−3.74 (m, 2H, 2CH, 3CH), 3.89 (d, J = 11.6 Hz, 1H, 10CH2), 3.94 (d, J = 11.6 Hz, 1H, 10CH2) ppm; 13 C NMR (125 MHz, CD3OD) δ 19.9 (8CH2), 26.2 (7CH2), 31.4 (9CH2), 50.5 (6CH2), 55.0 (4CH2), 59.0 (10CH2), 61.1 (9aCq), 70.2 (3CH), 74.6 (2CH), 76.9 (1CH) ppm; HRMS (ESI) Calcd for C10H20NO4: m/z = 218.1392 [M+H]+, Found m/z = 218.1397. NOESY correlation between 1H (δ 3.30−3.34) and 9H (δ 1.30−1.40), 1 H (δ 3.30−3.34) and 8H (δ 1.53−1.68) Dihydroxylation of Compound 8a. To a solution of compound 8a (87 mg, 0.15 mmol) in dry THF (2 mL) and water (100 μL) were added N-methylmorpholine N-oxide (47 mg, 0.40 mmol) and osmium tetraoxide (2.5 mol% in tBuOH, 115 μL, 0.01 mmol). The solution was stirred at room temperature during 18 h. The reaction was then quenched by a saturated solution of Na2S2O3. The aqueous layer was extracted three times with dichloromethane. The organic layers were washed with brine, dried over MgSO4, and the solvents were evaporated under reduced pressure. The crude oil was purified by chromatography on silica gel (pentane/AcOH 7:3, 5:5 and 1:9) to afford the diastereomers 10a (39 mg, 43%) and 10b (24 mg, 26%) as colorless oils. Some starting material was also recovered (10 mg, 12%). (2S,3R,7S,8R,9R,9aR)-7,8,9-Tris(benzyloxy)-9a-((benzyloxy)methyl)octahydro-1H-quinolizine-2,3-diol (10a). [α]20D +4 (c 1.22, CHCl3); IR ν 3390 (s), 3085 (w), 3070 (w), 3030 (m), 2925 (s), 2863 (s), 1497 (w), 1460 (m), 1358 (w), 1064 (s) cm−1; 1H NMR (500 MHz, CDCl3) δ 1.79 (dd, J = 5.5, 13.0 Hz, 1H, 9CH2), 1.85 (pt, J = 13.0 Hz, 1H, 9CH2), 2.93 (dd, J = 2.0, 14.5 Hz, 1H, 6CH2), 3.05−3.13 (m, 2H, 4CH2, 6CH2), 3.27 (dd, J = 4.0, 13.0 Hz, 1H, 4CH2), 3.41 (d, J = 10.0 Hz, 1H, 10CH2), 3.52−3.58 (m, 1H, 3CH), 3.66 (d, J = 10.0 Hz, 9870

DOI: 10.1021/acs.joc.7b01494 J. Org. Chem. 2017, 82, 9866−9872

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The Journal of Organic Chemistry

3302 (s), 2921 (m), 1647 (w), 1432 (w), 1066 (m) cm−1; 1H NMR (500 MHz, CD3OD, presat HOD) δ 1.73 (dd, J = 2.5, 15.5 Hz, 1 H, 9 CH2), 1.92 (dd, J = 3.5, 15.5 Hz, 1H, 9CH2), 2.53 (dd, J = 4.1, 13.8 Hz, 1H, 6CH2), 2.84−2.96 (m, 2H, 4CH2), 3.15 (pt, J = 12.0 Hz, 1H, 6 CH2), 3.28−3.38 (m, 1H, 2CH), 3.38−3.46 (m, 1H, 3CH), 3.55 (d, J = 9.5 Hz, 1H, 1CH), 3.58 (d, J = 11.6 Hz, 1H, 10CH2), 3.95−4.00 (m, 1H, 7CH), 4.03−4.07 (m, 1H, 8CH), 4.35 (d, J = 11.6 Hz, 1H, 10CH2) ppm; 13C NMR (125 MHz, CD3OD) δ 28.0 (9CH2), 49.5 (6CH2), 54.4 (4CH2), 61.9 (9aCq) 62.6 (10CH2), 63.0 (7CH), 68.7 (8CH), 71.1 (3CH), 73.4 (1CH), 75.9 (2CH) ppm; HRMS (ESI) Calcd for C10H20NO6: m/z = 250.1291 [M+H]+, Found m/z = 250.1294.

1H, 10CH2), 3.70−3.78 (m, 3H, 2CH, 7CH, 8CH), 3.81 (d, J = 8.0 Hz, 1H, 1CH), 4.34 (d, J = 11.5 Hz, 1H, BnCH2), 4.35 (d, J = 12.0 Hz, 1H, Bn CH2), 4.48 (d, J = 12.0 Hz, 1H, BnCH2), 4.58 (d, J = 11.5 Hz, 1H, Bn CH2), 4.61 (d, J = 12.0 Hz, 1H, BnCH2), 4.64 (d, J = 11.0 Hz, 1H, Bn CH2), 4.72 (d, J = 11.0 Hz, 1H, BnCH2), 4.78 (d, J = 11.5 Hz, 1H, Bn CH2), 4.87 (br s, 1H, OH), 7.17−7.21 (m, 2H, ArCH), 7.23−7.33 (m, 18H, ArCH) ppm; 13C NMR (125 MHz, CDCl3) δ 27.5 (9CH2), 52.4 (6CH2), 53.1 (4CH2), 61.7 (9aCq), 66.7 (10CH2), 67.1 (8CH), 68.6 (7CH), 72.0 (BnCH2), 73.6 (BnCH2), 74.4 (BnCH2), 75.1 (BnCH2), 77.9 (1CH), 78.5 (3CH), 80.9 (2CH), 127.7 (ArCH), 127.8 (ArCH), 127.8 (ArCH), 128.0 (ArCH), 128.1 (ArCH), 128.1 (ArCH), 128.4 (ArCH), 128.5 (ArCH), 128.5 (ArCH), 138.0 (ArCq), 138.5 (ArCq), 138.6 (ArCq), 138.7 (ArCq) ppm; HRMS (ESI) Calcd for C38H44NO6: m/z = 610.3169 [M+H]+, Found m/z = 610.3188. NOESY correlation (in toluene-d8) between 1H (δ 3.97 ppm) and 10H (δ 3.29 and 3.45−3.53 ppm), 2H (δ 3.77 ppm) and 9H (δ 1.83 ppm), 6H-α (δ 2.87 ppm) and 8 H (δ 3.41 ppm), 6H-α (δ 2.87 ppm) and 10H (δ 3.29 ppm). (2R,3S,7S,8R,9R,9aR)-7,8,9-Tris(benzyloxy)-9a-((benzyloxy)methyl)octahydro-1H-quinolizine-2,3-diol (10b). [α]20D +22 (c 0.90, CHCl3); IR ν 3362 (s), 3088 (w), 3063 (w), 3032 (w), 2924 (m), 2857 (m), 1496 (w), 1453 (m), 1363 (w), 1261 (m), 1069 (s) cm−1; 1 H NMR (500 MHz, CDCl3) δ 1.86 (dd, J = 3.0, 15.5 Hz, 1H, 9CH2), 2.07 (dd, J = 4.0, 15.5 Hz, 1H, 9CH2) 2.80 (dd, J = 4.5, 13.5 Hz, 1H, 6 CH2), 2.88 (dd, J = 8.5, 11.5 Hz, 1H, 4CH2), 3.09−3.21 (m, 2H, 4 CH2, 6CH2), 3.49 (d, J = 10.5 Hz, 1H, 10CH2), 3.56−3.64 (m, 2H, 2 CH, 3CH), 3.68 (d, J = 8.5 Hz, 1H, 1CH), 3.97−4.02 (m, 1H, 7CH), 4.04−4.08 (m, 1H, 8CH), 4.14 (d, J = 10.5 Hz, 1H, 10CH2), 4.26 (d, J = 11.0 Hz, 1H, BnCH2), 4.42 (d, J = 12.0 Hz, 1H, BnCH2), 4.58−4.70 (m, 4H, BnCH2), 4.79 (d, J = 11.0 Hz, 1H, BnCH2), 4.81 (d, J = 11.0 Hz, 1H, BnCH2), 7.10−7.14 (m, 2H, ArCH), 7.22−7.34 (m, 18 H, Ar CH) ppm; 13C NMR (125 MHz, CDCl3) δ 28.8 (9CH2), 50.2 6 ( CH2), 51.5 (4CH2), 60.6 (9aCq), 62.9 (7CH), 67.6 (8CH), 70.7 (10CH2), 72.8 (BnCH2), 73.7 (BnCH2), 75.1 (BnCH2), 75.4 (BnCH2), 78.2 (3CH), 79.7 (1CH), 82.4 (2CH), 127.5 (ArCH), 127.6 (ArCH), 127.8 (ArCH), 127.9 (ArCH), 128.0 (ArCH), 128.1 (ArCH), 128.3 (ArCH), 128.6 (ArCH), 137.8 (ArCq), 138.5 (ArCq), 138.7 (ArCq), 138.8 (ArCq) ppm; HRMS (ESI) Calcd for C38H43NO6: m/z = 610.3168 [M +H]+, Found m/z = 610.3188; NOESY correlation (in toluene-d8) between 2H (δ 3.60 ppm) and 9H (δ 1.78 ppm), 1H (δ 3.95 ppm) and 10 H (δ 4.22 ppm). (1R,2R,3S,7R,8S,9aR)-9a-(Hydroxymethyl)octahydro-1H-quinolizine-1,2,3,7,8-pentaol (11a). To a solution of 10a (19 mg, 0.03 mmol) in methanol (0.5 mL) was added 20% Pd(OH)2/C (7 mg, 0.05 mmol) and HCl (2 M in Et2O, 23 μL, 0.05 mmol). The suspension was stirred overnight under hydrogen (5 bar) then filtered over Celite. The Celite was rinsed with methanol and the filtrate was concentrated under vacuum. The residue was purified through a column of DOWEX 50W-X8 ion-exchange resin (H+ form), eluting with water and NH4OH (1 M). The hexahydroxylated quinolizidine 11a was obtained as a colorless oil (10 mg, quantitative). [α]20D +6 (c 0.86, MeOH); IR ν 3312 (s), 2919 (m), 1643 (w), 1449 (w), 1041 (m) cm−1; 1H NMR (500 MHz, CD3OD, presat HOD) δ 1.72−1.81 (m, 1H, 9CH2), 1.84− 1.94 (m, 1H, 9CH2), 2.96−3.11 (m, 2H, 4CH2, 6CH2), 3.22−3.52 (m, 3H, 2CH, 3CH, 6CH2), 3.60 (d, J = 8.8 Hz, 1H, 1CH), 3.70−3.84 (m, 3H, 4CH2, 10CH2), 3.85−3.95 (m, 2H, 7CH, 8CH) ppm; 13C NMR (125 MHz, CD3OD) δ 24.6 (9CH2), 53.7 (6CH2), 56.2 (4CH2), 60.2 (10CH2), 66.7 (8CH), 69.1 (7CH), 70.5 (3CH), 72.7 (1CH), 75.2 (2CH) ppm; HRMS (ESI) Calcd for C10H20NO6: m/z = 250.1291 [M +H]+, Found m/z = 250.1290. (1R,2R,3S,7S,8R,9aR)-9a-(Hydroxymethyl)octahydro-1H-quinolizine-1,2,3,7,8-pentaol (11b). To a solution of 10b (19 mg, 0.03 mmol) in methanol (0.5 mL) was added 20% Pd(OH)2/C (8 mg, 0.06 mmol) and HCl (2 M in Et2O, 25 μL, 0.05 mmol). The suspension was stirred overnight under hydrogen (5 bar) then filtered over Celite. The Celite was rinsed with methanol and the filtrate was concentrated under vacuum. The residue was purified through a column of DOWEX 50W-X8 ion-exchange resin (H+ form), eluting with water and NH4OH (1 M). The hexahydroxylated quinolizidine 11b was obtained as a colorless oil (8 mg, quantitative). [α]20D +4 (c 0.80, MeOH); IR ν

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01494. Copies of NMR spectra of all new compounds, description of enzyme inhibition evaluation including Lineweaver−Burk plots, and HPLC profiles of compounds 9a, 9b, 11a, and 11b (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*[email protected] *[email protected] ORCID

Alice Kanazawa: 0000-0001-7170-6551 Sandrine Py: 0000-0002-5143-7689 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS A.V.D.C. is grateful to Univ. Grenoble Alpes for a doctoral allocation. M. Fayolle (DCM) is thanked for the preparation of nitrone 4 and Laurine Buon (CERMAV, Grenoble) is thanked for performing HPLC analyses. We acknowledge support from ICMG FR 2607, Grenoble (through which NMR and MS analyses have been performed), and by the French National Research Agency in the framework of the “Investissements d’avenir” program Glyco@Alps (ANR-15-IDEX-02).

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REFERENCES

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DOI: 10.1021/acs.joc.7b01494 J. Org. Chem. 2017, 82, 9866−9872

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(17) In this case, transmetalation of the Grignard reagent may occur, and addition of an allylzinc species may be more selective than that of the corresponding Grignard reagent due to lower nucleophilicity. (18) (a) Malik, M.; Witkowski, G.; Ceborska, M.; Jarosz, S. Org. Lett. 2013, 15, 6214−6217. (b) Malik, M.; Ceborska, M.; Witkowski, G.; Jarosz, S. Tetrahedron: Asymmetry 2015, 26, 29−34 See also ref 7.. (19) Dihydroxylation of 8b was sluggish: one of the expected diols was identified as the major product (yield < 35%, estimated dr > 80:20), however this compound could not be purified sufficiently to allow determination of its configuration and subsequent debenzylation. (20) Gossan, D.; Alabdul Magid, A.; Kouassi-Yao, P.; Behr, J.-B; Ahibo, A.; Djakoure, L.; Harakat, D.; Voutquenne-Nazabadioko, L. Phytochemistry 2015, 109, 76−83. (21) Pawar, N. J.; Parihar, V. S.; Chavan, S. T.; Joshi, R.; Joshi, P. V.; Sabharwal, S. G.; Puranik, V. G.; Dhavale, D. D. J. Org. Chem. 2012, 77, 7873−7882.

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DOI: 10.1021/acs.joc.7b01494 J. Org. Chem. 2017, 82, 9866−9872