Our research program focused on the isolation, structure elucidation, and synthetic modification of biologically active, natural products derived from plants. Because the quantities of the active compounds isolated are usually small, the structure elucidation of the isolates is carried out primarily by spectroscopic methods. Of particular importance to the structure determination are mass spectroscopy and NMR spectroscopy, particularly two-dimensional NMR techniques such as COSY, HMBC, and HSQC. During the past twenty-eight years, graduate students and undergraduate students in my group have isolated and characterized compounds from many different classes of natural products, including flavonoids, triterpenes, phenylpropanoid glycosides, coumarins, acetogenins, alkaloids, and ansa macrolides, from plants found in all parts of the world .

Our recent interests involved work on compounds that are potentially active against leishmaniasis or that show antifungal activity. Recently we investigated the consituents of Citharexylum caudatum. This led to the isolation of six new iridoid glucosides, and a semi-synthetic approach to these monoterpenes has been developed. 

We also worked on the isolation and structure elucidation of new triterpene quinone methides from Salacia madagascariensis, a member of the family Celastraceae. One previously isolated member of this class of compounds, isoiguesterin, has demonstrated significant activity against Leishmania cultures, and some of the new compounds we have isolated show similar activity. We also investigated the reactions of these compounds to evaluate structure-activity relationships. 

Another plant of recent interest, Schrebera alata, showed antifungal activity against Rhodotorula glutinus. Among the constituents of S. alata we have isolated are secoiridoid glucosides and lignan glucosides.

In recent years, we have also isolated phenylpropanoid sucrose esters from two Polygonum species, both of which grow in Virginia. Vanicosides A –F were isolated from from Polygonum pensylvanicum guided by an assay for protein kinase C inhibition. Vanicosides A and B, perfoliatosides A-E, and four new 4-phenyldihydrocoumarins were subsequently isolated from Polygonum perfoliatum. We were also interested in synthesizing selected vanicosides, starting with sucrose, in order to prepare derivatives for structure-activity relationship (SAR) studies.

An ongoing interest of our program was the biologically active constituents of various Maytenus species. Two new maytansinoids, antineoplastic ansa macrolides, were isolated from Maytenus buchananii. We also investigated the preparation of derivatives of the diene region of this class of compounds to add to the SAR information for the maytansinoids. Guided by the brine shrimp lethality bioassay, we isolated new nicotinoyl sesquiterpene alkaloids from Maytenus putterlickoides.