Pocahemiketals A and B, two new hemiketals with unprecedented sesquiterpenoid skeletons from Pogostemon cablin

Pocahemiketals A and B (1 and 2), two novel hemiketal sesquiterpenoids with unprecedented skeletons, were isolated from the essential oil of the aerial parts of Pogostemon cablin. In addition to a bicyclo[3.2.1]-carbon core, 1 and 2 possessed a hemiketal α,β-unsaturated-γ-lactone moiety. Their structures were determined by extensive spectroscopic analysis, electronic circular dichroism calculation, and single-crystal X-ray diffraction. Compound 2 exhibited significant vasorelaxant activity against phenylephrine-induced contraction of a rat aorta ring with the EC50 value of 16.32 μM.

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