Investigation of Una De Gato I. 7-deoxylogauic acid and N-15 NMR spectroscopic studies on pentacyclic oxindole alkaloids from Uncaria tomentosa

The C-8-(S) isomer of deoxyloganic acid (7-deoxyloganic acid), together wit h beta -sitosteryl glucoside, five known stereoisomeric pentacyclic oxindol e alkaloids and the tetracyclic oxindole isorhyncophylline, were isolated f rom the inner bark of Uncaria tomentosa. Structures of the isolated compoun ds were based on H-1 and C-13 NMR data, mainly 2D NMR experiments, includin g H-1-C-13 HMBC and H-1-H-1 NOESY correlation. Furthermore, the hitherto un reported N-15 chemical shifts of the isomeric oxindole alkaloids, using H-1 -N-15 HMBC experiments, were utilized to facilitate their characterization. Uncarine D showed weak cytotoxic activity against SK-MEL, KB, BT-549 and S K-OV-3 cell lines with IC50 values between 30 and 40 mug/ml, while uncarine C exhibited weak cytotoxicity only against ovarian carcinoma (IC50 at 37 m ug/ml). (C) 2001 Elsevier Science Ltd. All rights reserved.