Preparative separation of methoxy derivatives of psoralen using supercritical-fluid chromatography

A method of separation of a mixture of three methoxy derivatives of psoralen—bergapten, xanthotoxin, and isopimpinellin—has been developed. The performed screening allows it to be concluded that it is appropriate to separate them by normal-phase supercritical-fluid chromatography (SCF). Analysis of mechanisms of separation of methoxypsoralens (MOPs) showed that, on all silica gel-based sorbents with immobilized polar groups, except for 2-ethylpyridine and pentafluorophenyl sorbents, absorption occurs by the same retention mechanism. A possible explanation for the observed regularities of elution of the related MOPs has been suggested. In the case of pentafluorphenyl sorbent, π-electronic intermolecular interactions play a key role in separation. Presumably the same effect is responsible for the particular order of elution observed when the 2-ethypyridine sorbent was used.