Synthesis of Cyclohexyl 6-O-Trityl-alpha-D-Threo-Hexopyranosid-4-ulo-(2,3:3',4')-2-Pyrazoline

[摘要] The isolation of the antibiotic streptomycin in 19441 and the presence of 2-deoxy-2-methylamino-L-glucosamine2 as one of its components gave an impetus to the study of amino sugar synthesis. Other antibiotics of this family are kanamycins,3 neomycins4 and gentamycins.5 Many antibiotics composed primarily of carbohydrates have been obtained from microorganisms and are called aminoglycoside antibiotics because they contain amino groups in their glycoside moieties.6 Prumycin, 4-(D-alanylamino)-2-amino-2,4-dideoxy-L-arabinose, having antitumor activity7 was synthesized8 from glycine and L-serine. Another amino sugar derivative has been shown to completely inhibit the derivation of tumor necrosis factor induced by 100 mg/mL Escherichia coli endotoxin.95-Amino-5-deoxy sugars are also known to be glycosidase inhibitors.10,11The importance of amino sugars described above led us to undertake the synthesis of cyclohexyl 3-amino-2-aminomethyl-2,3-dideoxy-a-D-talopyranoside 18 starting from 3,4,6-tri-O-acetyl-D-glucal 1.12 However, this communication reports the synthesis and characterization of 12 and 17 only.  Experimental General methods Melting points were determined with the Thomas Hoover (Unimelt) apparatus and are uncorrected. Elemental analyses were carried out at the Instituto de Química, Universidade de São Paulo and in the Department of Fundamental Chemistry of this University. IR spectra were recorded (nmax, cm-1) on a Perkin-Elmer models 467 and 237B spectrophotometers. NMR spectra were measured on a Varian 300 MHz or Bruker 200 MHz instruments in CDCl3 solution unless otherwise stated, and the chemical shifts are reported in parts per million downfield from TMS. Beckmann DB-G or Carl Zeiss-Jena instrument was used for recording the UV spectrum. Specific rotations were obtained on JASCO Model DIP-370 polarimeter. TLC was performed on plates coated with silica gel 60-G (E. Merck). Exposure of the plates to iodine vapors was used to reveal the spots. Silica gel G 70-200 mesh was used for gravitational column chromatography. Anhydrous magnesium sulfate was used to dry the extracts.Computational methodThe semi-empirical molecular orbital calculations (AM1)13 were carried out using MOPAC 93 program14,15 on an IBM RISC 6000 computer of this Department. Complete optimization of the geometry was achieved and the gradient norm dropped to 0.02. Cyclohexyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro -hex-2-enopyranoside (3) Tri-O-acetyl-D-glucal 1 (5.000 g, 18.38 mmol), cyclohexanol 2 (2.82 g, 28.2 mmol) in dry benzene (50 cm3) were stirred at room temperature, and boron trifluoride etherate (1 cm3) was added. The mixture was stirred for 40 min. During this time the solution turned dark brown. TLC (CHCl3-EtOAc 9:1) showed the presence of two spots: Rf = 0.25 (product) and other Rf = 0.18. The latter could either be due to unreacted 1 or to the b-anomer 4. The mixture was washed with a saturated aqueous solution of sodium bicarbonate (5 x 10 cm3), water (2 x 10 cm3), and dried over Na2SO4. Filtration and evaporation of the volatiles provided a brown-colored syrup, which was purified by chromatography using hexane-CHCl3 gradient to give 3 as a colorless syrup (3.29 g, 57%); [a]D25 + 111 ± 2° (c 3.3, CHCl3); IR nmax/cm-1 1750 and 1740 (COO) (neat); 1H NMR (200 MHz) d 5.7-5.9 (m, 2 H, H-2 and H-3), 5.30 (ddd, 3J4-5 9.0 Hz, 3J4-31.0 Hz, 4J4-2 1.0 Hz, 1 H, H-4), 5.17 (m, W/2 » 4.5 Hz, 1 H, H-1), 4.1-4.3 (m, 3 H, H-5, H-6 and H-6'), 3.64 (m, 1 H, O-CH), 2.08 (s, 3 H, OAc), 2.09 (s, 3 H, OAc), 1.1-2.1 (m, 10 H, 5 CH2). Elemental analysis: Found: C, 61.66; H, 7.86. Calc. for C16H24O6: C, 61.52; H, 7.74.Cyclohexyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro -hexopyranoside (5)Compound 3 (0.05 g, 1.6 mmol) in ethyl acetate (5 cm3) in the presence of PtO2 (0.01 g) was hydrogenated at 1 atm. for 12 h at room temperature. Filtration and solvent evaporation yielded 5 as a syrup in almost quantitative yield (one spot on TLC with the same Rf value in CHCl3-EtOAc 9:1 as that of 3); [a]D30.5 + 100° (c 0.8, CHCl3); 1H NMR (300 MHz): d 4.99 (s,br, W/2 » 4.5 Hz, 1 H, H-1), 4.6-4.8 (m, 1 H, H-4), 4.23 (dd, 2J6-6' 11.7 Hz, 3J6-5 5.6 Hz, 1 H, H-6), 4.10 (dd, 2J6'-6 11.7 Hz, 3J6'-52.3 Hz, 1 H, H-6'), 4.01 (ddd, 3J5-410.1 Hz, 3J5-65.6 Hz, 3J5-6'2.3 Hz, 1 H, H-5), 3.56 (m, 1 H, O-CH), 2.08 (s, 3 H, OAc), 2.05 (s, 3 H, OAc), 1.2-2.0 (m, 14 H, 7 CH2). Elemental analysis: Found: C, 61.18; H, 8.42. Calc. for C16H26O6: C, 61.13; H, 8.34.Cyclohexyl 2,3-dideoxy-a-D-erythro-hex-2-enopyranoside (6)A flask containing 3 (3.00 g, 9.62 mmol) in a solution (140 cm3) of MeOH-H2O-Et3N (9:6:1)16 was kept at room temperature for 1.5h. TLC in CHCl3-AcOEt-CH3OH (1.0:0.25:0.05) showed the disappearance of the starting material (Rf = 0.75) and the appearance of a new spot with Rf = 0.20. Evaporation and chromatography using CHCl3-hexane (1.0:0.43) gave 1.9g (86.7%) of 6 as hygroscopic crystals: m.p. 67-68oC (from EtOAc-cyclohexane); [a]D25 = + 46.0 ± 0.9o (c 3.4, CHCl3); IR nmax/cm-1 3600-3100 (OH) (Nujol); 1H NMR (300 MHz): d 5.95 (dt, 3J3-2 10.2 Hz, 4J3-1 » 1.3 Hz, 3J3-4 » 1.3 Hz, 1 H, H-3), 5.73 (ddd, 3J2-310.2 Hz, 4J2-4 2.4 Hz, 3J2-1 2.7 Hz, 1 H, H-2), 5.13 (m, 3J 1.3 Hz, 1 H, H-1), 4.20 (d,br 3J4-5 9 Hz, 1 H, H-4), 3.85 (d, 3J6-5 = 3J6'5 3.9 Hz, 2 H, H-6, H-6'), 3.75 (dt, 3J5-4 9.0 Hz, 3J5-6 = 3J5-6' 3.9 Hz, 1 H, H-5), 3.62 (m, 1 H, O-CH), 2.63 and 2.37 (s,br, exchangeable, 2 H, 2 OH), 2.04-1.10 (m, 10 H, 5CH2). Elemental analysis: Found: C, 61.19; H, 8.57. Calc. for C12H20O4.1/2 H2O : C, 60.72; H, 8.93.Cyclohexyl 2,3-dideoxy-a-D-erythro-hexopyranoside (7)Compound 6 (0.22 g, 0.93 mmol) in ethanol (20 cm3) and 5% Pd/C (0.02 g) was hydrogenated at room temperature and at atmospheric pressure for 24 h. TLC in CHCl3-benzene (19.0:1.0) showed a new product with Rf = 0.46. The product was purified by column chromatography using benzene initially followed by benzene-chloroform as gradient. Chloroform-benzene (1:1) eluted product 7 as a viscous liquid (0.10 g, 45% yield ): 1H NMR (300 MHz):d 4.92 (apparent dd, 3J1-2 1.5 Hz, 3J1-2¢ 3.0 Hz, 1 H, H-1), 3.84-3.71 (m, 2 H), 3.65-3.48 (m, 3 H), 2.69 (bs, s, 2 H, 2 OH), 1.96-1.10 (m, 14 H, 7 CH2).Cyclohexyl 2,3-dideoxy 6-O-trityl-a-D-erythro-hex-2-enopyranoside (8)Compound 6 (1.00 g, 4.38 mmol) in dry pyridine (5 cm3) and trityl chloride (1.43 g, 5.13 mmol) were stirred at room temperature under nitrogen for 72 h following the reported procedure.17 TLC showed only a trace of unreacted 6. Excess of the trityl chloride was destroyed by putting crushed ice into the flask and letting the contents to warm up to room temperature. The contents of the flask were diluted with CHCl3, transferred to a separatory funnel, washed with a saturated solution of sodium bicarbonate (3 x 5 cm3), water (2 x 5 cm3), and finally dried (Na2SO4). Solvent removal gave a viscous material which was chromatographed using initially benzene and followed by benzene-CHCl3 (19:1) to give 1.9 g (92.2%) of 8 as a semisolid material; [a]D25 = + 10o (c, 1; CHCl3); IR nmax/cm-1 3640-3120 (OH) and 1600 (C = C aromatic) (Nujol); 1H NMR (300 MHz) d 7.50-7.20 (m, 15 H, Ph-H), 5.89 (ddd, 3J3-2 10.1 Hz, 4J3-1 1,3 Hz, 3J3-4 1.7 Hz, 1 H, H-3), 5.72 (ddd, 3J2-3 10.1 Hz, 3J2-1 2.7 Hz, 4J2-4 2.1 Hz, 1 H, H-2), 5.10 (m, W/2 » 4 Hz, 1 H, H-1), 4.04 (m, 1 H, H-4), 3.90 (ddd, 3J5-6 5.5Hz, 3J5-6' 5.1 Hz, 3J5-4 9.0 Hz, 1 H, H-5), 3.67 (m, 1 H, O-CH), 3.42 (dd, 2J6'-6 9.7 Hz, 3J6'-5 5.1Hz, 1H, H-6'), 3.34 (dd, 2J6-6' 9.7 Hz, 3J6-5 5.5 Hz, 1 H, H-6), 2.30 (s, br,1 H, exchangeable, OH), 2.10-1.00 (m, 10 H, 5 CH2). Elemental analysis: Found: C, 77,51; H, 7.20. Calc. for C31H34O4. 1/2H2O: C, 77.63; H, 7.36.Cyclohexyl 2,3-dideoxy-a-D-glycero-hex-2-enopyranoside -4-ulose (9)Compound 6 (1.80 g, 7.90 mmol) was dissolved in dry CH2Cl2 (450 cm3) and freshly prepared activated MnO218 was added (18.50 g, 212.8 mmol). The mixture was stirred at room temperature for 4 hours. TLC (CHCl3) showed a new spot with Rf = 0.59 and the presence of some starting alcohol (Rf = 0.38). The mixture was filtered through diatomaceous earth and the clear filtrate was evaporated to give a semi-solid material. Chromatography using hexane initially followed by hexane-chloroform eluted the fast moving compound to furnish 1.0 g (56%) of 9: m.p. 99°-100 °C (from ether-petroleum ether); IR nmax/cm-1: 3600-3100 (OH, H bonded), 1690 (C = O conjugated) (KBr); 1H NMR (300 MHz): d 6.87 (dd, 3J2-3 10.2 Hz, 3J2-1 3.6 Hz, 1 H, H-2), 6.11 (d, 3J3-2 10.2 Hz, 1 H, H-3), 5.17 (d, 3J1-2 3.6 Hz, 1 H, H-1), 4.53 (t, 3J5-6 4.2 Hz, 1 H, H-5), 3.92 (dd, 2J6-6' 11.8 Hz, 3J6-5 4.2 Hz, 1 H, H-6), 4.02 (dd, 2J6'-6 11.8 Hz, 3J6'-5 4.2. Hz, 1 H, H-6'), 3.62-3.80 (m, 1 H, O-CH), 2.22 (s,br, exchangeable, 1 H, OH), 2.20-0.80 (m, 10 H, 5-CH2). Elemental analysis: Found: C, 63.42; H, 8.07. Calc. for C12H18O4: C, 63.72; H, 7.96.Cyclohexyl 2,3-dideoxy-6-O-trityl-a-D-glycero-hex-2 -enopyranosid-4-ulose (10)To a solution of 8 (1.00 g, 2.13 mmol) in CH2Cl2(250 cm3) was added freshly prepared and dried MnO218 (5.00 g, 57.5 mmol). The mixture was stirred for 4 h. TLC (CHCl3) showed the disappearance of 8. Filtration and evaporation of the solvent left a viscous material which was chromatographed using a mixture of benzene-CHCl3 (1.0:0.43) to give amorphous 10 (0.72 g, 72.4% yield): IR nmax/cm-1 1695 (C=O conjugated) (KBr); 1H NMR (300 MHz): d 7.50 - 7.20 (m, 15 H, Ph-H), 6.86 (dd, 3J2-3 10.2 Hz, 3J1-2 3.4 Hz, 1 H, H-2), 6.07 (d, 3J3-210.2 Hz,1 H, H-3), 5.49 (d, 3J1-2 3.4 Hz, 1 H, H-1), 4,70 (dd, 3J5-6 7.2 Hz, 3J5-6' 2.4 Hz, 1 H, H-5), 3.86 (m, 1 H, O-CH), 3.63 (dd, 2J6'-610.2 Hz, 3J6'-5 2.4 Hz, 1 H, H-6'), 3.44 (dd, 2J6-6' 10.2 Hz, 3J6-5 7.2 Hz, 1 H, H-6), 2.20-1.10 (m, 10 H, 5 CH2). Compound 10 was also prepared by tritylation of 9 in 86% yield.Cyclohexyl 6-O-trityl-a-D-threo-hexopyranoside-4-ulo -(2,3,:3',4')-2-pyrazoline (12)Compound 10 (0.10 g, 0.21 mmol) was dissolved in ether (5.0 cm3), and the freshly prepared diazomethane19 in ether was added dropwise at room temperature until the yellow color persisted.20 The crystals appeared gradually. Decantation of the ethereal layer provided 0.08 g (70.0%) of the crude product. Recrystallization from a large quantity of hot CH2Cl2 gave 12 (0.07g , 61.9%): m.p. 184°-186 °C; [a]D20 -200o(c 0.2, pyridine); IR nmax/cm-1 3322 (NH) and 1660 (C=O) (KBr); 1H NMR (300 MHz, pyridine-d5) d 9.92 (s,br, 1 H, N-H, exchangeable), 7.8 ¾ 7.1 (m, 15 H, Ph-H), 5.51 (d, 3J1-2 4.2 Hz, 1 H, H-1), 4.91 (t, 3J5-63J5-6' 4.8 Hz, 1 H, H-5), 4.24 (d, 3J 2.1 Hz, 1 H, H-7'), 4.03 (m, 1 H, O-CH), 3.90 (d, 3J6-53J6'-54.8 Hz, 2 H, H-6 and H-6'), 3.79 (unresolved, 2 H, H-2, H-7"), 2.2-1.1 (m, 10 H, cyclohexyl). Elemental analysis: Found: C, 74.40; H, 6.68; N, 5.25. Calc. for C32H34N2O4 .1/4H2O: C, 74.61; H, 6.75; N, 5.43.Cyclohexyl 1'-N-acetyl-4,6-di-O-acetyl-a-D-lyxo-hexo pyranoside-(2,3:3',4')-2-pyrazoline (17)Compound 9 (0.27 g, 1.2 mmol) was dissolved in ether (10 cm3) and to this solution was added diazomethane in ether dropwise at room temperature until the greenish yellow color persisted. TLC (CH2Cl2-EtOAc, 9:1) showed the disappearance of the substrate after 5 min. Solvent evaporation left 15 which was hydrogenated (10 atm) in EtOAc (10 cm3) at room temperature overnight in the presence of 0.020 g of PtO2. Filtration and solvent evaporation under vacuum furnished intermediate 16, which was acetylated and purified by chromatography (hexane-EtOAc 7:3) to give 17 (0.21 g, 45.7%): m.p. 117-118 °C (hexane- ether); 1H NMR (300 MHz): d 5.85 (d, 3J5-45.1 Hz, 1 H, H-4), 4.85 (d, 3J1-26.3 Hz, 1 H, H-1), 4.57 (ddd, 3J5-4 = 3J5-64.3 Hz, 3J5-6' 8.4 Hz, 1 H, H-5), 4.33 (dd,3J6-57.8 Hz, 2J6-6'12.3 Hz, 1 H, H-6), 4.25-4.10 (m, 3 H, H-6', H-7'', OCH), 3.73 (dd, 3J7'-27.5 Hz, 2J7'-7''12.0 Hz, 1 H, H-7'), 3.28 (quintet, 3J » 6 Hz, 1 H, H-2), 2.25 and 2.17 (two s, 6 H, OAc), 2.06 (s, 3 H, NAc), 1.90-1.20 (m, 10 H, 5 CH2). Elemental analysis: Found: C, 57.16; H, 7.37; N, 6.87. Calc. for C19H28O7N2 : C, 57.56; H, 7.12; N, 7.06.  Results and Discussion Reaction of tri-O-acetyl-D-glucal 1 with cyclohexanol 2 and a catalytic quantity of boron trifluoride etherate using the previously reported procedure,21 provided cyclohexyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro -hex-2-enopyranoside 3 as the main product (Scheme 1). The b-anomer which was probably formed as the minor product was inseparable from the unreacted 1 and no effort was made to isolate it. Column chromatography furnished 3 as a thick viscous liquid. Its 1H NMR agreed with the proposed structure but the configuration a became clear only after catalytic reduction of the C-2-C-3 double bond (3®5). The J1-2coupling constants in the a- and b-2,3-unsaturated hexopyranosyl glycosides are known to be similar.22 Consequently, evaluation of the anomeric configuration on the basis of these couplings alone is difficult. The 300 MHz 1H NMR spectrum of the reduced product 5 showed a signal of the anomeric proton as a broad singlet having a half-width of ca 4.5 Hz. This value together with a coupling constant J4-5 10.1 Hz proves that 5 is an a anomer which adopts 4C1 conformation. Observed couplings are incompatible with the b configuration.Deacetylation of 3 using triethylamine in methanol16 gave 6. Tritylation at the primary OH group14 furnished 8, which in turn was subjected to the allylic oxidation at C-4 with activated MnO2 to give the enone 10. The same compound was obtained by performing the allylic oxidation first (6®9) followed by tritylation (9®10), however the former sequence gave a better yield. Compound 6 was also hydrogenated to give cyclohexyl 2,3-dideoxy-a-D-erythro-hexopyranoside 7. Addition of diazomethane to C-2-C-3 double bond in 10 occurred from the opposite side of the cyclohexyl function to give a transient product 11 which rapidly tautomerized to 12 (Scheme 2).20 An alternative approach of CH2N2 from the same side is unlikely due to the bulky aglycon. It has already been shown earlier20 that much smaller ethoxy group in ethyl 6-O-acetyl-2,3-dideoxy-a-D-glycero-hex-2-enopyranoside-4-ulose 13 controlled the approach of CH2N2 in the same way as in our

[学科分类] 化学（综合）