Structural analysis of some bis-(8-isopropyl-isoquinolinium) derivatives reveals a preferential folded conformation leading to a stereoselective attack by sodium borohydride

摘要

Reduction of symmetrical bis-isoquinolinium derivatives with sodium borohydride generatesnormally a mixture of three 1,2,3,4-tetrahydroisoquinoline stereoisomers. In a series of 8-isopropyl analogues, chiral resolution failed for the analogues with propyl and m-xylyl linkerssince two and one peaks respectively were detected by HPLC. Further analysis by MS andCD of both peaks of the propyl analogue revealed that each peak corresponds to anenantiomer. Conformational analysis and X-ray cristallography showed a folded conformationof the propyl and m-xylyl analogues responsible for the observed stereoselectivity followingthe reduction step. Additional 1H NMR investigations confirm structural features detected bytheoretical analysis.