Three New D-Lactone Ring Isomeric Phragmalin-Type Limonoids from Chukrasia tabularis var. velutina

Abstract

Three new D-lactone ring isomeric phragmalin-type limonoids, tabulalins G-I (1-3), were isolated from the stem barks of Chukrasia tabularis var.velutina.Compound 1 possesses C-16/C-30 δ-lactone ring (D), which was unusual in phragmalins, and that of 2 and 3 were C-16/C-17.The structures of these three new compounds were elucidated on HR-ESI-MS, 1D and 2D NMR including HSQC, HMBC, and ROESY experiments.Chukrasia tabularis var.velutina (Wall.)][7][8][9][10] In most reported phragmalins, D ring is a -lactone ring forming between COOH-16 and C-17.But in our research, many kinds of phragmalins with C-16/C-30 -lactone ring were isolated, such as C-15-acyl phragmalin-type limonoids orthoesters, 8 13/14/18-cyclopropanyl phragmalins, 10 and normal phragmalin-type orthoesters. 11Further investigation on the limonoids of title plant led to the isolation of three new D-lactone ring isomeric phragmalin-type limonoids, tabulalins G-I (1-3).The main difference between compounds 1-3 was the location of D-lactone ring, which of compound 1 was C-16/C-30 δ-lactone ring and compounds 2-3 was C-16/C-17 ones.The structures of these new compounds were elucidated on their extensive 1D and 2D spectroscopic analysis (HSQC, HMBC, and ROESY) and HR-ESI-MS.Herein, the isolation and structural elucidation of them are reported.