11 STRUCTURE OF PONCITRIN
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A new coumain derivative, C_<20>H_<22>O_4, mp 93-94°, was isolated from the root of Poncirus trifoliata Rafi. It was named poncitrin, and hydrogenated to give tetrahydroponcitrin. Poncitrin and tetrahydroponcitrin have been investigated by means of the nuclear magnetic resonance spectroscopy, and of the nuclear Overhauser effect measurments. It was suggested that the structure of poncitrin corresponds to be (3). A further experiments have been carried out by chemical degradations of poncitrin and its derivatives. Hydrogenation of poncitrin proceeded stepwise to give tetrahydroponcitrin (15) and hexahydroponcitrin (16), respectively. Degradation of (15) with aqueous sodium hydroxide and methyl sulfate resulted in O-methyltetrahydroponcitrinic acid (17). Catalytic hydrogenation of (17) gave the corresponding dihydro derivative (18). Degradation of (16) under the same conditions as the degradation of (15) also afforded (18). However, degradation of (3) under the same conditions as the degradations of (15) and (16) gave trans-cycloponcitrinic acid(19a) or the mixture of trans- and cis-cycloponcitrinic acid (19a and 19b). Hydrogenation of either 19a, or 19a and 19b yielded cyclotetrahydroponcitrinic acid (20). Permanganate oxidation of (3) produced a-hydroxyisobutyric acid which indicated the presence of a 2, 2-dimethylchromene ring in the molecule. Hydrolytic fission of (3) resulted in a phloroglucinol derivative. Treatment of (20) with hydrobromic acid gave compound (21). These data indicate that the structure of poncitrin is that of formula (3).
