Theisolation andcharacterisation ofanewtype ofdimeric adenine photoproduct inUV- irradiated deoxyadenylates

A new type of dimericadeninephotoproduct has been isolatedfrom d(ApA)irradiated at 254 nm in neutralaqueoussolution.It is formedin comparableamountsto another,quitedistinct,adeninephotoproductfirst describedby Porschke(J.Am. Chem.Soc. (1973),95, 8440-8446).Results from highresolutionmass spectrometryand H NKR indicatethat the new photoproductcomprisesa mixtureof two stereoisomerswhose formation involvescovalentcouplingof the adeninebasesin d(ApA)and concomitant incorporation of theelementsof onemoleculeof water. The photoproduct is degradedspecifically by acid to 4,6-diamino-5-guanidinopyrimidine (DGPY) whose identityhas been confirmedby independentchemicalsynthesis. Formation of thenew photoproduct inUV-irradiated d(pA)2and poly(dA),but not poly(rA),has beendemonstrated by assayingtheiracidhydrolysates for the presenceof DGPY. The properties of the photoproductare consistent with it being generatedby the hydrolyticfissionof an azetidine photoadduct inwhichtheN(7)andC(8)atomsof the5'-adenineind(ApA)are linkedrespectively to theC(6)andC(5)positionsof the3'-adenine.