Twelve novel and diverse 16-norphragmalin-type limonoids from Chukrasia tabularis var. velutina

A series of novel and structurally related C-15-acyl 16-norphragmalin-type limonoids, chuktabrins C-J (1-8) and chuktabularins U-X (9-12), were isolated from the stem bark of Chukrasia tabularis var. velutina. Their structures were established on the basis of detailed spectroscopic analysis, and the absolute configuration of compound 1 was determined by a single-crystal X-ray study using a mirror CuKα radiation. Compounds 7 and 8 were unprecedent C-15-acyl 16-norphragmalins with ketonic alkyl appendage at C-15, and compounds 4 and 8 were first examples of limonoid with a characteristic carbonate moiety esterified at OH-9/OH-8 or OH-1/OH-8 respectively. A biosynthetic pathway of these limonoids was reasonably presumed based on the novel and diverse structures isolated, which provides a new insight into the plausible biosynthesis of C-15-acyl 16-norphragmalin-type limonoids. The anti-inflammatory activity of major isolates were evaluated for inhibitory activity against lipopolysaccharide (LPS) induced nitric oxide (NO) production in macrophage (RAW264.7) cell line, with IC(50) value ranging from 2.40 to 16.90 μM.