Oxygen Exchange Studies and Resolution Attempts With Vanadyl Etioporphyrin I.

Vanadyl etioporphyrin I has C4 symmetry and is chiral. Hence,
it should be resolvable. Attempts were made to resolve it into its
enantiomers by chromatography using optically active ads or bents since
it has no functional groups which can be used to form isolable
diastereomers. Numerous optically active ads or bents were tried in the
pure state and adsorbed on silica gel. In most cases the Rf values were
either close to zero or close to one, making resolution impossible. Only
in the case of lactose on silica gel and using benzene as the solvent was
the Rf value such (approx. 0. 52) that resolution seemed, at least, possible.
However, no optically active fraction could be obtained on column
chromatography. Since oxygen exchange between the vanadyl group of vanadyl
etioporphyrin I and water might occur and cause rapid interconversion
of the enantiomers (hence racemization), thereby vitiating resolution
attempts, the possibility of such oxygen exchange was investigated under
a variety of conditions by means of H2 O^18 . The I. R. method was used to
detect any such exchange (VO^18 vs. VO^16). It was found that vanadyl etioporphyrin
I fails to undergo any measurable exchange under all the conditions
tried, although the vanadyl ion of vanadyl sulfate does undergo
exchange.