A CHEMICAL SCREENING STRATEGY FOR THE DEREPLICATION NATURAL PRODUCTS EXTRACTS AND PRIORITIZATION OF HIV-INHIBITORY AQUEOUS

Assmn.-A relatively high percentage (ca. 15%) of aqueous extracts from terrestrial plants, cyanobacteria, and marine invertebrates and algae has exhibited activity in the National Cancer Institute’s primary AIDS-antiviral screen. By removal of anionic polysaccharides in a first stage of dereplication, we have eliminated from further consideration a considerable number of these extracts. However, a still substantial proportion of the active extracts remained, from which we wished to select and prioritize a small percentage for our detailed bioassaydirected fractionation studies. Therefore, a chemical screening protocol, utilizing various solid-phase extraction cartridges, has been developed for a second-stage dereplication and to assist in prioritization of these extracts for our further investigations. In late 1987, the National Cancer Institute began an extensive evaluation of natural product extracts derived from microorganisms, plants, and marine invertebrates and algae for HIV-inhibitory activity (1). In the intervening five years, nearly 40,000 crude aqueous and organic solvent extracts have been tested in the primary anti-HIV screen (2). The overall status of the NCI anti-HIV primary screening of crude aqueous extracts through October 1992, is summarized in Table 1. A surprisingly large number (ca. 15%) of the aqueous extracts of terrestrial plants and lichens, cultured cyanobacteria, and marine invertebrates and algae has exhibited some activity in the screen. The high percentage of active extracts strongly suggested the presence of one or more recurring compound classes with HIV-inhibitory activity. In order to help focus our NCI intramural research efforts upon a limited number of extracts, we first developed and are applying a simple precipitation strategy for the initial dereplication (elimination) of extracts containing anti-HIV-active sulfated polysaccharides (3). This procedure has substantially decreased the number of leads retained for further consideration. However, a considerable proportion of the supernatant fractions contain HIV-inhibitory activity not apparently associated with sulfated polysaccharides. Therefore, we sought to develop a protocol for the preliminary general chemical characterization of these AIDS-antiviral aqueous extracts which we could apply to a second stage of dereplication and subsequent prioritization of a practical number of extracts for our further study. We had been experimenting with solid phase extraction cartridges to scout for fractionation approaches suitable for our aqueous extracts. In so doing, it occurred to us that we might be able to utilize this scouting technique for a preliminary chemical characterization, or “chemical screening,” as a follow-up stage of selection from the remaining active extracts. Such an approach would allow us to gain insight into the general chemical nature of potential new leads, to identify and dereplicate additional recurring classes of antiviral compounds, and to select chromatographic procedures for initial fractionation of the remaining extracts of greatest interest to us.