Open-chain nitrogen compounds. Part XII. Methanolysis of 3-alkyl-3,4-dihydro-1,2,3-benzotriazin-4-ols: evidence for ring-chain tautomerism with the cytotoxic monoalkyltriazenes

A series of 4-hydroxy-3,4-dihydro-1,2,3-benzotriazines ("triazinols"), potential pro-drugs for the cytotoxic monoalkyltriazenes, have been investigated for anti-tumor activity and have been found to have marginal activity against the TLX5 tumor. The in vivo anti-tumor activity correlates with previously observed in vitro cytotoxicity of the compounds. The chemical behaviour of the triazinols is consistent with carbinolamine triazene ring-chain tautomerism in solution. The triazinols undergo methanolysis to give a series of new 4-methoxytriazines; the rate of methanolysis is primarily dependent on the substituent at C-4 of the triazinol. Those triazinols that undergo methanolysis rapidly are also more active biologically, suggesting that cytotoxicity and anti-tumor activity derive from the insitu generation of the open chain triazene.