Synthesis of enantiomerically pure fire ant venom alkaloids: Solenopsins and isosolenopsins A, B and C
作者:H. M. T. Bandara Herath、N. P. Dhammika Nanayakkara
DOI:10.1002/jhet.5570450112
日期:2008.1
Concise and efficient methods for the synthesis of enantiomers of fireantvenomalkaloidssolenopsin and isosolenopsin A, B, and C are described. These syntheses are based on diastereoselective electrophilic substitution of enatiomerically-pure α-lithiated 2-alkylpiperidine.
Solenopsins A, B and C have been synthesized in enantiomericallypure forms from the corresponding anti-1,5-diols which have been obtained from glutaric anhydride by an asymmetric synthesis induced by chiral sulfoxides.
A newenantioselective total synthesis of (−)-solenopsin B was described starting from L-glutamic acid as an optically active natural source, in which stereoselectivereduction of bicyclic N,O-ketals with DIBALH was used as the key reaction step.
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.