Objective Novel Diels-Alder-type adducts from the stems and branches of Morus nigra were investigated, and their peroxisome proliferator-activated receptor gamma (PPARγ) binding activity was preliminarily evaluated. Methods Systematic isolation and purification were carried out by multiple chromatographic methods including silica gel, AB-8 macroporous resin, polyamide, Sephadex LH-20 gel and ODS reversed-phase column chromatography. Structures of the isolated compounds were identified by modern spectroscopic techniques including high-resolution electrospray ionization mass spectrometry（HR-ESI-MS）and nuclear magnetic resonance spectroscopy (¹H-NMR, ¹³C-NMR). The in vitro activities of some compounds were evaluated by PPARγ ligand-binding assay. Results Six Diels-Alder adducts were isolated from the ethanol extract of M. nigra twigs and identified as (5aR,10aR,14S)-2-((1S,2R,3S)-2-(2,4-dihydroxybenzoyl)-2',4'-dihydroxy-5-methyl-1,2,3,6-tetrahydro-[1,1'-biphenyl]-3-yl)-1,3,8, 14-tetrahydroxy-13,13- dimethyl-11H-10a,5a-(epoxypropano)benzofuro[3,2-b]chromen-11-one (1), sanggenon O (2), sanggenon C (3), mulberrofuran F (4), cathayanin B (5), and mulberrofuran G (6). Compound 1 exhibited weak PPARγ ligand-binding activity at 10 μmol/L. Compound 3 exhibited moderate ligand-binding activity toward PPARγ at 10 μmol/L, which was obviously weaker than that of its biosynthetic precursor sanggenol F (SGF). Conclusion Compound 1 is a new compound, named nigragenon Q, it is formed by an intermolecular [4+2] cycloaddition between a sanggenone-type dihydroflavone and a chalcone. Oxidation of the C-2 isoprenyl side chain enables its connection to C-3 via an oxygen bridge, furnishing a six-membered ring and constructing a unique [4,4,3] bridged ring system. Compound 3 exhibited moderate PPARγ ligand-binding activity.

Moraceae  /  Morus nigra L.  /  Diels-Alder-type adducts  /  nigragenon Q  /  peroxisome proliferator-activated receptor γ