ABSOLUTE-CONFIGURATION OF THE SOLENOPSINS, VENOM ALKALOIDS OF THE FIRE ANTS

An effective and practical procedure has been developed that allows the assignment of the absolute configuration of solenopsins from diverse origins using only small amounts of material. The method is based on the transformation of the natural secondary amines into diastereoisomeric amides by reaction with (R)-2-methoxy-2-phenyl-2-(trifluoromethyl)acetic acid chloride (MTPA-Cl), followed by comparison of their chromatographic behaviour with those of standards of established absolute configuration, This procedure has been applied to three samples of ants: Solenopsis geminata workers, S. invicta workers and S. invicta alates. It has been found that the absolute configuration of the trans alkaloids is always (2R,6R) while that of the cis alkaloids is (2R,6S). Moreover, a new synthesis of enantiomerically pure solenopsin A (4) and isosolenopsin A (3) starting from L-alanine is presented.