Structure-activity relationships of the truncated norzoanthamines exhibiting collagen protection toward anti-osteoporotic activity.

The marine alkaloid norzoanthamine is a candidate drug for osteoporosis treatment. Due to its structural complexity, simplified analogues possessing similar biological activities are needed for further research. Recently, we found that the bisaminal unit, representing two-thirds of the original structure, is a bioactive equivalent. We synthesized three kinds of further truncated norzoanthamines and evaluated their collagen protection activities. No analog with collagen protection activity comparable to that of the bisaminal unit was found. Thus, we confirmed the importance of the bisaminal unit for the collagen protection activity. Furthermore, we found that the recognition tolerance of the substrate collagen is relatively large by comparing both enantiomers.