5‐Methoxypsoralen photoadduct formation: conversion of monoadducts to crosslinks

5‐Methoxypsoralen is often substituted for 8‐methoxypsoralen in the photochemotherapy of psoriasis even though the nature of the resulting photadducts in cellular DNA has not been determined. A recent molecular mechanics study with a model oligonucleotide predicted that intercalated 5‐methoxypsoralen molecules would tend to favor the preferential formation of 3,4‐monoadducts. Such a result would be contrary to the photoadduct patterns observed with other psoralens. In this study we show that 5‐methoxypsoralen photoadducts formation is, in fact, very similar to that for other psoralens, i.e., the primary photoadduct is the 4′,5′‐monoadduct which can be quantitatively converted to crosslink.