Two new cyclopentadecane antibiotics, named mangromicins A and B, were
separated out from the culture broth of
Lechevalieria aerocolonigenes K10-0216.
The chemical structures of the two novel compounds were elucidated by
instrumental analyses, including various NMR, MS and X-ray crystallography.
Mangromicins A and B consist of cyclopentadecane skeletons with a
tetrahydrofuran unit and a 5,6-dihydro-4-hydroxy-2-pyrone moiety.
Mangromicins A and B showed
in vitro antitrypanosomal activity with IC
50 values of 2.4 and 43.4 μg/ml, respectively. An enantioselective total synthesis of
(+)-mangromicin A has also been accomplished. The tetrahydrofuran ring of
mangromicin A, possessing a tetrasubstituted carbon center, was constructed by
Mukaiyama-type vinylogous alkylation via a cyclic oxocarbenium intermediate
derived from a γ-hydroxy ketone with ideal stereoselectivity, and the
4-hydroxydihydropyrone scaffold was generated via Dieckmann condensation at a
late stage of the total synthesis. The reliable asymmetric synthesis of
(+)-mangromicin A has revealed the absolute configuration of naturally occurring
mangromicin A.
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