Irradiation of thin films consisting of 4,5',8-trimethytpsoralen (TMP)
, adenosine and small amounts of alcohols led to TMP-alcohol photoaddu
cts in addition to TMP-adenosine photoadducts. Four TMP-ethanol and tw
o TMP-methanol adducts have been separated and characterized. Covalent
bonds were formed between the 4-carbon of TMP and the alpha-carbon to
the hydroxy group in the alcohols. The TMP-alcohol photoadducts were
for-med only in the TMP film containing small amounts of alcohol and a
denosine. Furthermore, no photoadduct of TMP and ribose was detected u
pon phototysis of a TMP-ribose film, suggesting that the adenine moiet
y plays a specific role in the reaction. The interaction of adenosine
with psoralens in a dry film may be related to the DNA sequence select
ivity observed for the photoreaction of psoralens with DNA.