Pyrazole derivatives. 5. Synthesis and antineoplastic activity of 3-(2-chloroethyl)-3,4-dihydro-4-oxopyrazolo[5,1-d]-1,2,3, 5-tetrazine-8-carboxamide and related compounds.

Two pyrazolotetrazine derivatives were synthesized as the analogous prodrugs of the light-sensitive antineoplastic agents dacarbazine and BIC. Both the pyrazole derivatives are stable under ordinary light illumination. Biological evaluation of these pyrazoles revealed that the compound containing a 2-chloroethyl function (6a) demonstrated good antineoplastic activity in experimental animals, but the one containing a methyl function (6b) was inactive. The inactivity of compound 6b may suggest that compound 6a and related imidazotetrazines may simply act as biological alkylating agents per se rather than as prodrugs. The information could also imply that the postulated dealkylation mechanism for the triazene derivatives should be reexamined.