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A number of new natural products have been isolated from medicinal plants. A novel isomerisation of 19—S—vindolinine to 19—R—vindolinine is described. The two syntheses of the anti—cancer drug vinblastine reported by us were based on a semi—synthetic approach developed on a novel biogenetic hypothesis first proposed by us visualising catharanthine and vindoline as the biosynthetic precursors to these anti—cancer drugs. Continuing studies on the isolation of these precursors as well as vinbias— tine itself have resulted in 20—50 fold increases in yields of vinblastine from the leaves of Catharanthus roseus. NEW ALKALOIDS FROM COCCULUS PENDULUS Cocculus pendulus (Forst) Diels (Menispermaceae) is a scandent shrub growing in areas around Karachi. The roots of the plant are used in the indigenous system of medicine for the treatment of intermittent fevers and as a tonic. Hypotensive and anti—cancer activity has been attributed to the alkaloidal fractions from the leaves and stem. Our recent studies on this plant have resulted in the isolation and structure elucidation of the following new alkaloids: 12—0—methylkohatinel, 5—hydroxyapateline 2, 5'—hydroxytelobine 3, dehydrokohatine 4, 12—0—methyldehydrokohatine 5, l,2—dehydro—2,—nortelobine 6, siddiquamine 7, siddiquine 8, l,2—dehydrokohatine—2, N—oxide 9, cocsupendine 10 and 0,O—dimethyl—l, 2—dehydronorkohatine 11 (ref.1) 12—0—Methylkohatine 1 (ref.1) [aID = 9940 (CHC13) I.R. (CHC13), 3351 (N—H) U.V. (MeOH) Xmax233 mu (log a 4.35), 235 mu (log a 4.35), 274 nm (log a 3.52) and 2.88 mu (log a 3.51), Xlnin 234 nm (log a 4.351), 280 mu (log a 3.52) 'HWrfl (360 Mhz, CDC13 + 2 drops CD300,cS):2.60 (s, 311, N—CH3),3.95 (s, 311, O—C113),3.96 (s, 311, O—C113),4.01 (d, 1H, J = 9.2Hz, H—l),6.62 (s, 111, H—5),6.25 (s, 111, H—8),6.60 (d, 111, J = 2Hz, H—l0),6.91 (d, 111, 3 8.2Hz, H—13),6.83 (dd, 111, j1 = 2.lHz, 2 = 8.2Hz, I1—14),6.77 (dd, 111, .J = l.89Hz, j2 8.1Hz, H—1l),7.01 (dd, 111, J1 = 1.811z, J2 = 8.2Hz, H—10),7.20 (dd, 111, j1 = 1.89Hz, j2 = 8.1 Hz, H—13),7.52 (dd, 111, j1 = l.82Hz, 2 = 8.1Hz, H—14).M.S. m/z 578 (Mt, 47%), 351 (100%), 335 (25%).

Isolation, structural and synthetic studies on the chemical constituents of medicinal plants of Pakistan