X-ray structure and13C NMR assignments of indole alkaloids fromAspidosperma cruenta
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The leaf tissue ofAspidosperma cruenta was studied for alkaloid content. Two alkaloids were isolated and shown by a combination of MS, X-ray, and high field NMR analysis to be obscurinervine and obscurinervidine. X-ray analysis of obscurinervine provided the first quantitative structural information on this compound. Obscurinervine (C25H30N2O5) crystallized in the monoclinic space groupP21 with unit cell parametersa=12.863(3)Å,b=9.646(2)Å,c=18.484(3)Å,β=105.14(5)°,V=2213.8(8)Å3,Dc=1.316 Mg/m3, andZ=4. The structure was solved by direct methods and refined toR=0.054 for 3468 observed reflections. The 2D INADEQUATE NMR experiment provided the first13C chemical shift assignments for obscurinervine. Nineteen of the 2313C-13C connections present were detected. Corresponding13C assignments for obscurinervidine were made by comparison to the spectrum of obscurinervine. The average natural concentrations of the alkaloids were determined to be 0.780% (obscurinervine) and 0.737% (obscurinervidine) by HPLC analysis. Obscurinervine was tested for antiviral and cytotoxic effects. Noin vitro activity was observed.
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