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Michael Addition Artifacts of Major Withanolides in Physalis longifolia
Five artificial withanolides 1-5, including three new compounds 1 – 3, were isolated and identified as derivatives of the three major withanolides 6-8 naturally present in Physalis longifolia. These artifacts formed in the presence of methanol through intra/inter-molecular Michael additions at the β-carbon of α, β-unsaturated carbonyl moiety in ring A. The mechanism was further confirmed by using deuterated methanol. As methanol is extensively used in withanolide isolation and purification, a comprehensive literature investigation was also conducted to identify potential withanolide artifacts reported to date.