Reductive activation of mitomycin C.

Abstract

Mitomycin C, an antitumor antibiotic, is known to require reductive activation in order to function as an alkylating agent. In this work reduction has been carried out by using radiolytically produced formate radicals that reduce mitomycin C to its semiquinone in a clean rapid one-electron reaction. The ultimate products of the reduction are cis- and trans-2,7-diamino-1-hydroxymitosene (B1 and B2) and 2,7-diaminomitosene (C). The yields of these compounds were found to be the same when the rate of reduction was varied by 11 orders of magnitude. At pH 7, one mitosene molecule is formed for every two formate radicals, while at pH 9.1, about eight mitosene molecules are formed per formate radical. The ratio of (B1 + B2)/C is less than 0.4 at pH 5.7, 1.0 at pH 7, and greater than 3.5 at pH 9.1. Observations have been made of changes in optical absorption due to the formation of the semiquinone and hydroquinone of both mitomycin C itself and 2,7-diamino-1-hydroxymitosene (B). The direct conversion of the semiquinone form of mitomycin C into the semiquinone of B proceeds slowly, if at all. The semiquinone form of B will rapidly reduce mitomycin C (k = 7.2 X 10(8) M-1 s-1). The hydroquinone of mitomycin C undergoes changes resulting in the formation of B and C. The yields of B and C depend on pH.(ABSTRACT TRUNCATED AT 250 WORDS)