Polyene substrates with unusual methylation patterns to probe the active sites of three catalytic antibodies

The synthesis of two tetraenes that differ in their methylation pattern from the natural substrate in lanosterol biosynthesis, 2,3-oxidosqualene, and their examination with three catalytic antibodies is described. The design of these novel, linear terpenoid structures was governed by initial results obtained from the characterization of the three catalytic antibodies. These were generated by immunization with a steroidal hapten that mimics multicyclization without the necessity for anti-Markovnikov additions or ring expansions. Such a reaction cascade would represent a more 'primitive' version compared to the oxidosqualene cyclization observed in lanosterol, cycloartenol and beta-amyrin biosynthesis and would not require a tail-to-tail connection of the third and fourth isoprene unit as seen in squalene. The first tetraene design (A) only contains trisubstituted double bonds and hence its synthesis starts from farnesol and tris-norgeraniol. The second tetraene design (B) is considered the more precise match to the inducing hapten that generated the antibody collections by exhibiting one disubstituted double bond and its synthesis utilizes a tris-norgeraniol derivative and a symmetrical bis-allylic alcohol as key building blocks. Chromatographic comparison studies lead to the conclusion that the currently studied antibodies also produce monocyclic products from the two substrates as has been formerly observed with a squalene-derived substrate. In contrast, 2,3-oxidosqualene is not accepted by these catalysts supporting the notion that the current substrates are fully bound by recognition of both terminal functional groups.