REACTION OF ANTHRACYCLINE ANTITUMOR DRUGS WITH REDUCED GLUTATHIONE - FORMATION OF AGLYCON CONJUGATES

Anaerobic reduction of adriamycin (1) with bi(3,5-dimethyl-6-(hydroxymethyl)-2-oxomorpholin-3-yl)(DHM-3 dimer), bi(3,5,5-trimethyl-2-oxomorpholin-3-yl)(TM-3 dimer), or dithionite in the presence of excess reduced glutathione (GSH, 9) yielded the aglycon conjugate, 7-deoxy-7-S-glutathionyladriamycinone (11a,b), as a mixture of diastereomers together with 7-deoxyadriamycinone (12) via 7-deoxyadriamycinone quinone methide. Anaerobic reaction of adriamycin with reduced glutathione also yielded, in a slower reaction, the conjugates with the glutathione serving both as the reducing agent and as the nucleophile reacting with the quinone methide, as proposed in Scheme 2. A separate reductive cleavage of 11a,b to 12 established reversibility of the nucleophilic addition. The proposed mechanism was further supported by the reaction composition at termination as a function of conditions (Tables 1 and 3). At higher concentrations of 1 and 9, a 99% yield of salt 13, consisting of the anion of 11b and adriamycin cation, precipitated and was characterized spectroscopically. The conjugate 11b was subsequently separated from adriamycin by extraction. The anthracyclines daunomycin (2) and menogaril (10) also reacted with glutathione with and without an additional reducing agent to yield the respective aglycon conjugates, 7-deoxy-7-S-glutathionyldaunomycinone (14a,b) and 7-deoxy-7-S-glutathionylnogarol (15a,b), characterized predominantly by HPLC electrospray mass spectrometry. Enzyme-catalyzed formation of 11a,b may be relevant to tumor cell resistance to adriamycin.