[CH2:1]([C:3]1([OH:26])[C:23]2[CH:22]=[C:21]3[N:9]([CH2:10][C:11]4[C:12]3=[N:13][C:14]3[CH:15]=[CH:16][CH:17]=[CH:18][C:19]=3[CH:20]=4)[C:8](=[O:24])[C:7]=2[CH2:6]OC1=O)[CH3:2].C(#N)C.Cl([O-])(=O)(=O)=O>CN(C)C=O.O>[CH3:6][C:7]1[C:8](=[O:24])[N:9]2[C:21](=[CH:22][C:23]=1[C:3](=[O:26])[CH2:1][CH3:2])[C:12]1=[N:13][C:14]3[C:19]([CH:20]=[C:11]1[CH2:10]2)=[CH:18][CH:17]=[CH:16][CH:15]=3A sample of 4.6 g of 4-ethyl-4-hydroxy-1H-pyrano[3',4':6,7]-indolizino[1,2-b]quinolin-3,14(4H,12H)-dione [(20 S) camptothecin] was stirred with 46 ml of N,N-dimethylformamide. The suspension was heated at reflux, and the disappearance of starting material was monitored by HPLC (C18 reverse phase column, 20-25% acetonitrile:water mobile phase, perchlorate buffer at pH approximately 3.0). The reaction was monitored by UV detection at a wavelength of 228 nm. The only responses detected under these conditions were a peak for N,N-dimethylformamide near the solvent front, a peak for the starting material and a peak for the desired product with a retention time of approximately 3.2 relative to the starting material. The reaction was heated until consumption of the starting material was complete (approximately 8 days). After cooling to ambient temperature the solid product was collected by filtration, and washed with methanol. After drying under vacuum to a constant weight 3.48 g (87%) of product, m.p. 233°-234° C. was obtained.
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