The amide hydrogen of (-)-indolactam-V and benzolactam-V8's plays a critical role in protein kinase C binding and tumor-promoting activities.

To investigate the role of the amide hydrogen of (-)-indolactam-V (1) and benzolactam-V8's on protein kinase C (PKC) binding and tumor promotion, 8-decylbenzolactone-V8 (6), a new lactone analogue of 8-decylbenzolactam-V8 (4), was synthesized from 2-nitrophenylpyruvic acid (7) in 11 steps. The PKC binding ability and tumor-promoting activities in vitro of 6 were much lower than those of 1 and 4, suggesting that the amide hydrogen of 1 and benzolactam-V8's plays a critical role in tumor promotion. However, it is noteworthy that 6 showed significant selectivity in the PKC isozyme surrogate binding.