Six New 3,5-Dimethylcoumarins from Chelonopsis praecox, Chelonopsis odontochila and Chelonopsis pseudobracteata

Ten 3,5-dimethylcoumarins (1-6 and 8‒11) involving six new ones (1-6), together with a known 3-methylcoumarin (7), were isolated from the aerial parts of three Chelonopsis plants, C. praecox, C. odontochila, and C. pseudobracteata. The structures of the new compounds were determined by extensive HRESIMS, 1D and 2D NMR spectroscopic analyses. According to the substitution at C-5, these coumarins were classified into 5-methyl, 5-hydroxymethyl, 5-formyl, and 5-nor types. All the isolates were assayed for their inhibition on α-glucosidase, protein tyrosine phosphatase 1B, and T-cell protein tyrosine phosphatase in vitro.