The reductive deglycosylation of adriamycin in aqueous medium: a pulse radiolysis study

The free radical (II) produced by one-electron reduction of adriamycin (I) exists in aqueous solution at pH 7.0 in equilibrium with the parent and the two-electron reduced form (III). Over some hundreds of milliseconds deglycosylation takes place yielding an aglycone (IV) which subsequently rearranges to form a more stable aglycone, 7-deoxyadriamycinone (V). The changes in the optical absorption spectrum accompanying these processes are reported. The rate constant for III----IV is 1.1 s-1 and for IV----V is 1.5 x 10(-2) s-1. At pH 4.0 the two electron reduced form of adriamycin exists predominantly in a different tautomeric form (VII). It is suggested that this deglycosylates via a free radical mechanism involving the acidic form of the semiquinone free radical (VI).