Enzymes in organic synthesis : aldolase-catalyzed reactions for the synthesis of unusual sugars

Abstract

Several aspects of the use of enzymes in organic synthesis have been explored. Fructose-1,6-diphosphate aldolase (FDP aldolase) is available commercially and has been cloned and overexpressed in E. coli. Both aldolases have been used in the synthesis of highly substituted piperidine and pyrrolidine derivatives. The microbial aldolase appears to have the same substrate specificity as the FDP aldolase from rabbit muscle. Of the alkaloids synthesized, the most interesting are 1-deoxynojirimycin (DNJ) and 1-deoxymannojirimycin (DMJ), DNJ and DMJ can be converted to castanospermine and its 6-epimer. Both of these compounds are useful as anticancer and antiviral agents. DNJ is easily converted to N-butyl-DNJ, which is an efficient inhibitor against HIV infected cells. Its inhibitory effects are thought to be due to the disruption of cell fusion and subsequently cell-cell transmission. The use of chiral 3-azido-2-hydroxy aldehydes were accomplished by lipase resolution of 2-acetyl-3-azidopropanal acetal. Both (R)- and (S)-aldehydes are obtained >98% ee and >95% isolated yields. The lipase resolution of various 3-substituted-2-acetylated propanal acetals were examined. 2-Acetylated-3-chloro and 3-fluoro propanal acetals were resolved with >98% ee and >92% isolated yields. The resolved chloro propanals are easily converted to the corresponding chiral 2-(diethoxymethyl) oxirane. The oxiranes can be converted to the corresponding thiirane and aziridine derivatives. An improved procedure for the chemical synthesis of dihydroxyacetone phosphate (DHAP) has been prepared. This procedure is efficient, uses inexpensive starting materials, and is suitable for large scale synthesis. This preparation should make aldolase chemistry more attractive to organic chemists and to industrial applications involving aldolase reactions. L-Rhamnulose-1-phosphate aldolase and L-Fuculose-1-phosphate aldolase were used with the arsenate methodology. These two aldolases were shown to accept the dihydroxyacetone arsenate ester as a substrate in place of DHAP. The arsenate methodology is compatible with aldolases and also indicates the broad applicability of this methodology to organic synthesis.