A catalytic enantioselective route to hydroxy-substituted quaternary carbon centers: Resolution of tertiary aldols with a catalytic antibody

Aldolase antibody 38C2-catalyzed resolutions of tertiary aldols were studied. Tertiary aldols proved to be very good substrates for antibody catalyzed retro-aldol reactions. The catalytic proficiency, (k(cat)/K-M)/k(uncat), of the antibody for these reactions was on the order of 10(10) M-1. A fluorogenic tertiary aldol allowed for the quantitative study of enantiomeric excess as a function of reaction conversion, revealing an E value of ca. 160 in this case. Study of a variety of substrates demonstrated that antibody-catalyzed retro-aldolization provides rapid entry to highly enantiomerically enriched tertiary aldols, typically >95% ee, containing structurally varied, heteroatom-substituted quaternary carbon centers. The utility of this approach to natural product syntheses has been demonstrated with the syntheses of (+)-frontalin, the side chain of Saframycin H, and formal syntheses of (+)- and (-)-mevalonolactone.