Phytochemical and pharmacological studies on some species of Annonaceae

This thesis describes the phytochemical investigation of five species of Annonaceae, Cleistopholis glauca, Cleistopholis patens, Piptostigma fasciculata, Goniothalamus thwaitesii and Goniothalamus gardneri. Extracts of specific parts of each plant were fractionated using standard chromatographic techniques and pure compounds isolated identified on the basis of their physical and spectral data (IR, UV, MS, ID and 2D NMR). The stem bark of Cleistopholis glauca yielded fourteen compounds. These included the tri- and tetrarhamnosides, cleistri- and cleistetrosides with cleistetroside-6 and -7 as new compounds, famesane sesquiterpenes including the new methyl-(2E,6E)-10-oxo-3,7,1 1-trimethyldodeca-2,6-dienoate, flavonoids, simple aromatic compounds, the azaanthracene alkaloid cleistopholine and the neolignan rel-(2a,3β)-7-O-methylcedrusin. This represents the first report of rel-(2a,3β)-7-O methylcedrusin in the family, of flavonoids in the genus and of cleistopholine in the species. The leaves of Cleistopholis patens afforded seven compounds. These were six cleistri- and cleistetrosides, with cleistrioside-2, -3, -4 and cleistetroside-6 being new, and shikimic acid. This is the first report of shikimic acid in the genus and of cleistri- and cleistetrosides in the species. The leaves of Piptostigma fasciculata yielded three compounds, which included the sesquiterpene β-caryophyllene-4,5-oxide, the diterpene (2ξ, 7ξ, 1 1ξ)-phytol and the flavonol glycoside nicotiflorin. This is the first report of (2ξ, 7ξ, 1 1ξ)-phytol in the family and of all three compounds in the genus. The aerial parts of Goniothalamus thwaitesii afforded five compounds. These were the triterpenes ffiedelinol, friedelin and betulinic acid, the flavonol glycoside meamsitrin and the flavonol-3-O-methyl ether annulatin. This is the first report of friedelinol, betulinic acid, meamsitrin and annulatin in the family and of all compounds in the genus. The aerial parts of Goniothalamus gardneri afforded nine compounds. These included eight flavonoids and the new acetogenin, rel-5a-hydroxymethyl-3β-eicosa-19’-en-1 1’-yn-tetrahydrofuran-2-one (goniothalamusin). Among the flavonoids, 2’,4’-dihydroxy-4,6’-dimethoxychalcone and dihydroflavokawain A are reported for the first time as natural products. All compounds are isolated for the first time in the family. A bioassay-guided search for new bradykinin antagonists in the crude extracts of the two Cleistopholis species was carried out using a radioligand binding assay on bradykinin receptors. The compounds showing affinity for the receptors were identified as the cleistri- and cleistetrosides.

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