Triterpenoid pyrazines and benzopyrazines with cytotoxic activity.

Twelve lupane, 18alpha-oleanane, and des-E-lupane derivatives (1a-5b) were either extracted from natural sources or synthesized from betulinic acid (1a) and betulin (2). Compounds 1b, 1c, 3b, 3c, 4b, 4c, 5a, and 5b were then used as starting materials for further synthesis of a series of pyrazines and benzopyrazines (6a-18); 20 of them are new (6a-6e, 7a-7d, and 10a-18). Activity of pyrazine 6a against the T-lymphoblastic leukemia cell line CEM encouraged us to synthesize several new esters (6b-6d) to study structure-activity relationships with respect to substitution of the carboxyl group at position 28. The synthesized compounds were tested for cytotoxicity against a variety of cancer cell lines of different histogenetic origin, and the results were compared with cytotoxicity of the known starting compounds. Significant cytotoxic activity against A 549, K 562, and multidrug-resistant K 562-tax cell lines was found in pyrazines 6a, 6d, and 6e.