Vibrational spectroscopy of betulinic acid HIV inhibitor and of its birch bark natural source.

Raman and IR spectra of betulinic acid (BA) (3beta-hydroxy-20(19) lupaen-28 oic acid) and of the natural birch bark have been successfully recorded and discussed. A high selectivity of the Raman technique was remarked for evidencing the betulin in the birch bark. Surface enhanced Raman spectrum (SERS) of BA on colloidal silver has been obtained. The presence and shifting of the symmetric stretching mode of the COO group in the SERS spectrum suggests a chemisorption of the steroid structure on the metallic particles.