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 conde nsation of nitromethane and chloroacetaldehyde, protection of the resu lting 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 diast ereomeric amino alcohols 6a,b. A reproducible ratio of > 90: 10 6a/6b was obtained using freshly prepared hydride reagent. The amino alcohol s were converted to the corresponding (R,R*)-amide 6c and (R*,S*)-ami de 6d which were chromatographically separated. The(R,R*)-amide was t ransformed 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.