OvoA
in ovothiol biosynthesis is a mononuclear non-heme iron enzyme
catalyzing the oxidative coupling between histidine and cysteine.
It can also catalyze the oxidative coupling between hercynine and
cysteine, yet with a different regio-selectivity. Due to the potential
application of this reaction for industrial ergothioneine production,
in this study, we systematically characterized OvoA by a combination
of three different assays. Our studies revealed that OvoA can also
catalyze the oxidation of cysteine to either cysteine sulfinic acid
or cystine. Remarkably, these OvoA-catalyzed reactions can be systematically
modulated by a slight modification of one of its substrates, histidine.
A synthesis of natural aculeatin D has been achieved, with the key stereogenic centers taken from inexpensive and readily available D-xylose. In elaboration of D-xylose into a desired form readily applicable in synthesis a previously misinterpreted and overlooked abnormal selectivity in hydroxyl protection was noticed and exploited. Protocols were developed for monotosylation of a triol insoluble in CH2Cl2 and "freezing" the less stable isomer (aculeatin D) at the PIFA-mediated oxidative spirocyclization, respectively. An unexplained deprotonation at a benzyl protecting group by a thermodynamically more stable dithiane carbanion in the literature was also addressed.
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