1572
C. SANFILIPPO et al.
spectrometer with tetramethylsilane as internal standard. Chemical shifts are reported in ppm (8)
and coupling constants (J) are given in Hz. 2D NMR (COSY and C-H correlation) experiments
were performed using standard Bruker microprograms. GC analysis were performed on a HP-5, 5%
phenylmethylsilicone or Chiraidex G-DA (dialkyl y-cyclodextrin) capillary columns, N2 as carrier
gas, flame ionization detector.
Oxidation of cis-l,2-dihydro©'cyclohexa-3.5-diene
N-Methylmorpholine-N-oxide (550 mg, 4.70 mmol) and OsO4 (12 mg, 0.05 mmol) were added to
a solution of cis-1,2-dihydroxycyclohexa-3,5-diene (500 mg, 4.46 mmol) in CH2C12 (50 mL). The
resulting mixture was stirred at 4°C for 24 h, then quenched by evaporation of the solvent. The
residue was subjected to standard acetylation (Ac20 in pyridine) followed by column chromatography
(acetone/CH2C12 1:9 vol/vol as the eluent) affording, after crystallization from ethyl acetate/hexane,
380 mg of 1,2,3,4-tetra-O-acetylconduritol D (27% yield) and 880 mg of (_+)-l,2,3,4-tetra-O-
acetylconduritol E (63% yield) (_+)-2.
General procedure for small-scale enzymatic alcoholysis of (+_)-2
Enzyme (20 mg/mL) and n-BuOH (23 ~L/mL, 2 equiv) were added to a solution of (___)-2 (10
mg/mL) in tert-butylmethyl ether (t-BME). The suspension was stirred at 300 rpm and 45°C and the
progress of the reaction monitored by GC analysis of aliquots, injected after acylation with propionic
anhydride/pyridine. The reaction was stopped by filtering off the enzyme and the solution was taken to
dryness. The residue was subjected to chromatography on Si Diol eluting with ethyl acetate/hexane (4:6
vol/vol). Enantiomeric excesses (ee) of (+)-2 were determined by GC analysis. The stereochemistry
of (+)-2 was assigned by chemical correlation with (+)-conduritol E.
Preparative enzymatic alcoholysis of (+_)- 1,2,3,4-tetracetyloxy-o, clohex-5-en e, (+_)-2
Lipozyme® IM (500 mg) and n-BuOH (0.44 mL~ 4.83 mmol) were added to a solution of (_+)-2 (250
mg, 0.79 mmol) in t-BME (25 mL). The reaction mixture was stirred at 45°C and 300 rpm for 5 h (conv.
22%), the suspension was filtered and the filtrate taken to dryness. The residue was chromatographed
on Si Diol (ethyl acetate/hexane 4:6 vol/vol) to give (1R)-hydroxy-(2R,3R,4R)-triacetyloxycyclohex-
5-ene, ( - ) - 3 (43 mg, 20% yield), [~x]D -200 (c 0.8, CHC13). IH NMR: 5 2.02 (3H, s), 2.06 (3H, s),
2.13 (3H, s), 4.53 (1H, dd, J=4.2 and 4.0), 5.33 (IH, dd, J=9.8 and 4.0), 5.47 (IH, dd, J=9.8 and 4.0),
5.62 (1H, dd, J=4.5 and 4.0), 5.81 (1H, dd, J=9.9 and 4.5), 6.00 (1H, J=9.9 and 4.2), 13C NMR:
20.67, 20.82, 20.87, 65.11, 66.49, 66.69, 69.30, 126.15, 131.33,169.97, 170.20, 170.26. Conventional
acetylation of ( - ) - 3 afforded (-)-2, ee >95%, [0t]o -245 (c 0.8, CHCI3).
In an analogous experiment the incubation time was protracted to a total of 48 h. The reaction
mixture was chromatographed on Si Diol (ethyl acetate/hexane 2:3 vol/vol) to give (+)-2 (240 mg,
48% yield); ee >95% [c~]D +244 (c 1.6, CHCI3). This ester by treatment with dil. NH4OH gave
(+)-conduritol E (+)-1 (115 mg, overall yield 49%). The more polar fractions, containing partially
acylated compounds, were pooled and taken to dryness. The residue was hydrolysed as above to give
(-)-conduritol E (-)-1 (110 mg, 47% yield); ee >95%, [~x]D -280 (c 0.3, H20), (lit.6b [a]D -294
(c 1, H20)).
Preparation of (- )-(1S,2R,3R, 4R)-l-amino-2,3, 4-trihydro~'-cyclohex-5-ene (Conduramine F-4), (-)-
4
A toluene solution (4 mL) containing triphenylphosphine (115 rag, 0.44 mmol), phthalimide (65
rag, 0.44 mmol) and diethyi azodicarboxylate (0.070 mL, 0.44 mmol) was added to a toluene (4 mL)
solution of ( - ) - 3 (100 rag, 0.37 mmol). The reaction mixture was shaken at rt and monitored by TLC
analysis. After 3 h the suspension was filtered and methylamine (40% aqueous solution, 4 mL) was
added to the filtrate. Stirring at rt was maintained for 15 min. The aqueous layer was then separated
and after elimination of methylamine by evaporation under reduced pressure applied to a Dowex-50
W (H+ form) column. The product (47 mg, yield 88%) was recovered by elution with 2N NH4OH: