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7-Ethylcamptothecin (1d), a model which does not have any site on the A-ring for further modification was converted into water-soluble derivatives by opening the E-ring lactone. 1d was heated in N,N-dimethylenediamine to yield amide 2a, and this was then acylated to furnish 3a-q, which were soluble in water as their HCl salts. The propionyl (3b), butyryl (3c) and methylthiopropionyl (3h) derivatives showed higher activity than the sodium salt of 1d. The acyl group makes the derivatives more lipophilic, and ease of hydrolysis of amide 2a to 1d is thought to be necessary for significant activity.

Chemical Modification of an Antitumor Alkaloid, 20(S)-Camptothecin. E-Lactone Ring-Modified Water-Soluble Derivatives of 7-Ethylcamptothecin.