The spatial structure of 13α-hydroxy-2-thionosparteine – a potential hypoglycemic agent – and some related compounds

Abstract 13α-Hydroxy-2-thionosparteine ( 7 ) was synthesized from 13α-hydroxylupanine ( 4 ) via 13α- t -butyldimethylsilyloxylupanine ( 8 ) and 13α- t -butyldimethyl-2-thionosparteine ( 9 ). The similarity of the stereochemistry of compounds 4 , 8 and 9 as well as 13α-trimethylsilyloxylupanine ( 10 ) was established on the basis of their 13 C and 1 H NMR spectra. In solution, the conformation with ring C a boat predominates in all compounds studied. However, they differ in the fraction of conformers: the thiolactams have a slightly greater population of the chair conformer than lactams and the hydroxy derivatives have a bit greater population of the same conformer than the parent lactam lupanine ( 2 ) or thiolactam 2-thionosparteine ( 5 ). The fraction of the chair conformer in 7 amounts to ca. 22%, almost as much as in multiflorine ( 6 ) known to be a good hypoglycemic agent. The trialkylsilyloxy derivates have a similar composition at the conformational equilibrium as that of the appropriate hydroxy compounds. The substituent does not influence the geometry of ring D.