X-RAY STRUCTURE AND C-13 NMR ASSIGNMENTS OF INDOLE ALKALOIDS FROM ASPIDOSPERMA CRUENTA

The leaf tissue of Aspidosperma cruenta was studied for alkaloid conte nt. Two alkaloids were isolated and shown by a combination of MS, X-ra y, and high field NMR analysis to be obscurinervine and obscurinervidi ne. X-ray analysis of obscurinervine provided the first quantitative s tructural information on this compound. Obscurinervine (C25H30N2O5) cr ystallized in the monoclinic space group P2(1) with unit cell paramete rs a=12.863(3)Angstrom, b=9.646(2)Angstrom, c=18.484(3)Angstrom, beta= 105.14(5)degrees, V=2213.8(8)Angstrom(3), D-c=1.316 Mg/m(3), and Z=4. The structure was solved by direct methods and refined to R=0.054 for 3468 observed reflections. The 2D INADEQUATE NMR experiment provided t he first C-13 chemical shift assignments for obscurinervine. Nineteen of the 23 C-13-C-13 connections present were detected. Corresponding C -13 assignments for obscurinervidine were made by comparison to the sp ectrum of obscurinervine. The average natural concentrations of the al kaloids were determined to be 0.780% (obscurinervine) and 0.737% (obsc urinervidine) by HPLC analysis. Obscurinervine was tested for antivira l and cytotoxic effects. No in vitro activity was observed.