20-O-β-Glucopyranosyl Camptothecin from Mostuea brunonis:  A Potential Camptothecin Pro-Drug with Improved Solubility

Bioassay-guided fractionation of the organic extracts of whole plants of Mostuea brunonis (Loganiaceae), using the National Cancer Institute's (NCI) human tumor-based in vitro antitumor screen, led to the isolation and identification of camptothecin 20-O-β-d-glucoside (1) and three moderately cytotoxic alkaloids, the known deoxypumiloside (2) and strictosamide (3), and the new 2‘-O-acetylstrictosamide (4), from the cytotoxic alkaloid fractions. While the previously unknown 20-O-β-d-glucopyranosyl camptothecin exhibited greater solubility in alcohol, DMSO−H2O and H2O than camptothecin, it was essentially inactive in the NCI's in vitro 60-cell line primary antitumor screen. However, it could be vulnerable to de-glucosidation in vivo, and may, therefore, merit additional evaluation as a potential prodrug of camptothecin that could be more readily formulated than the parent agent.