Limonoids and alkaloids from Tetradium austrosinense (Hand.-Mazz.) T.G.Hartley.

A pair of new enantiomeric indolopyridoquinazoline-type alkaloids, (+)-1,7 S ,8 R - and (−)-1,7 R ,8 S -trihydroxyrutaecarpine (3a and 3b), and a new limonoid-tyrosamine hybrid, austrosinin (8), along with six known alkaloids and limonoids, were isolated from the stems with leaves of Tetradium austrosinense. Their structures were elucidated on the basis of analysis of MS, NMR, ECD and time-dependent density functional theory-based electronic circular dichroism (TDDFT-ECD) calculations, as well as proposed biosynthetic pathway. An anti-inflammatory bioassay in vitro showed 8 had significant immunosuppressive effect against the production of pro-inflammatory cytokine TNF-α in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. [Display omitted] • Six alkaloids and three limonoids were isolated from Tetradium austrosinense. • A pair of enantiomeric indolopyridoquinazoline-type alkaloids were isolated and resolved. • Austrosinin is the first example of limonoid-tyrosamine hybrid from the nature source. • Austrosinin displayed significant immunosuppressive effect. [ABSTRACT FROM AUTHOR]