A class of 4-aza-lithocholic acid-derived haptens for the generation of catalytic antibodies with steroid synthase capabilities

The syntheses of a class of three haptens derived from the same 4-aza-stero idal skeleton is described. The sequence begins with oxidative cleavage of ring A of commercially available, optically pure lithocholic acid. Insertio n of nitrogen at position 4 and stereoselective hydrogenation of the result ing electron-rich enelactam under 600 psi H-2 yielded a system analogous to testosterone-5-alpha-reductase inhibitors. Upon exhaustive reduction of th is compound with lithium aluminium hydride, a linker for bioconjugation was attached before the N-oxide key functionality is established in ring A. Th is functional group is believed to be a true transition-state mimic for the electronic nature of initiation of the cationic cyclization of 2,3-epoxy-s qualene derivatives. In addition, it also holds promise for eliciting acidi c residues as part of a bait-and-switch strategy. Remarkably, both N-oxide epimers obtained from mCPBA oxidation can be separated by column chromatogr aphy on a 60 mg scale and were used in enantiopure form for separate immuni zations. Reliable configurative assignment was carried out by comparison st udies with previously characterized and published systems. A catalytic anti body (HA8-25A10) was obtained from the immunization with the hapten bearing an aminoxide oxygen in the beta position. Surprisingly, an inhibition stud y showed that the isomer with the inverted configuration at the N-oxide bou nd more strongly to this catalytic antibody. (C) 2000 Elsevier Science Ltd. All rights reserved.