Novel modification of 5-formyluracil by cysteine derivatives in aqueous solution.

Reactivities of 5-formyl-2'-deoxyuridine (fdU) and its 5'-monophosphate (fdUMP) to amino acids, amines and thiol compounds in neutral aqueous solution have been studied to elucidate the postmodification of the 5-formyluracil (fU) moiety in cells. fdU and fdUMP specifically reacted with cysteine and its analogs to form thiazolidine derivatives. The reaction involved condensation of the formyl group of fU with both alpha-NH2 (or NH2 at the equivalent position) and SH groups of cysteine derivatives.