np9b00524_si_001.pdf (703.75 kB)
Spontaneous Stereoselective Oxidation of Crystalline Avermectin B1a to Its C‑8a‑(S)‑Hydroperoxide
journal contribution
posted on 2019-12-12, 22:43 authored by Jan A. Gliński, John Proudfoot, Izabela Madura, Huaping Zhang, Michał Gleńsk, Victor Day, Marta K. DudekProlonged storage of technical abamectin as well as avermectin
B1a samples yielded a previously unknown derivative, designated
here as compound 1. Detailed NMR analysis and X-ray crystallography
allowed us to determine the structure of this compound and revealed
the presence of a hydroperoxide group (−OOH) attached stereoselectively
with configuration S to the C-8a carbon. This surprising
result involves the formation of the peroxide bond in solid crystalline
avermectin B1a upon exposure to air with no involvement
of light or recognized catalytic factors and is consistent with a
topotactic mechanism for the oxidation reaction. Compound 1 is stable in the absence of reducing agents and has potential as
a starting point in structural modification of the tetrahydrofuran
ring of avermectin B1a. It could also serve as a marker
in assessing the quality of stored technical abamectin.