2-AMINO-2-DEOXYTETROSE DERIVATIVES - PREPARATION FROM 4,5-DIHYDROISOXAZOLES VIA REDUCTIVE CLEAVAGE

The 4-alkoxy-3-nitro-4,5-dihydroisoxazoles 2a,b were prepared by condensation of nitromethane and chloroacetaldehyde, protection of the resulting nitroaldol Ic, and subsequent nitrosative cyclization. Multistep replacement of the nitro group of 2a,b by a 2-(1,3-dithiolanyl) group gave 7a,b. Reaction of 7b with lithium borohydride afforded reductive cleavage of the dihydroisoxazole ring to produce the open-chain diastereomeric amino alcohols 6a,b. A reproducible ratio of > 90: 10 6a/6b was obtained using freshly prepared hydride reagent. The amino alcohols were converted to the corresponding (R*,R*)-amide 6c and (R*,S*)-amide 6d which were chromatographically separated. The(R*,R*)-amide was transformed into the 2-amino-2-deoxythreose derivatives 11a,b and hence to 12 while the (R*,S*)-amide was similarly transformed to 2-amino-2-deoxyerythrose derivative 14a and its anomeric isomer 14b.