Analgesic corynanthe-type alkaloids from Strychnos angustiflora.

Nine new corynanthe-type alkaloids ( 1–9 ) and five known analogues ( 10–14 ) were isolated from the seeds of Strychnos angustiflora . Their structures were established based on extensive spectroscopic and spectrometric data, and the structure of 1 was confirmed using single-crystal X-ray crystallography. Based on NMR and electronic circular dichroism (ECD) data analyses, the R absolute configuration of the N-4 stereogenic center of 2 was shown to be opposite to that of 1 . In addition, the configurations of compounds 4–8 were established by hydrolysis experiments, and the antirhine moieties were determined to be identical to 11 , which was confirmed for the first time using single-crystal X-ray crystallography data analysis. Compounds 1 , 4 , 10 , and 11 exhibited analgesic activity, which increased the hind-paw licking latency rates by 56–78% at an intraperitoneal dose of 20 mg kg −1 during a hot-plate test in mice. [ABSTRACT FROM AUTHOR]