Natural products (NP's) are a significant source for both drug discovery and development of synthetic organic chemistry. The current renaissance of interest in NP's originates in technological advances that allow high-throughput screening, sub-nanomole analytical techniques and chemical genetics approaches to exploit minute quantities of naturally occurring compounds for drug discovery. Concurrently, advances in synthetic organic chemistry have demonstrated the applicability of multistep natural product synthesis to 'gram-scale' procurement of complex biologically active NP's, such as the macrolide polyketides phorboxazole and discodermolide, for preclinical and clinical testing. Analytical methods such as microcapillary NMR and mass spectrometry are amenable to NP's that are not suitable for X-ray crystallography, however, methods for determination of stereochemistry are still lacking. In order to capitalize on the convergence of sub-nanomole structure elucidation of anti-tumor natural products and macro-scale synthesis, and subscribe to priorities of the NIH Roadmap in molecular discovery, we propose development of a suite of methods for isolation and elucidation of stereochemistry of natural products at sub- nanomole amounts.
Aim 1 will extend our recently-described method for determining relative and absolute configuration of acyclic 1,n-diols (n greater than or equal to 5) to double-skipped tetraols and pentaols using exciton coupling circular dichroism in nanoscale-liposomes to polyols (e.g. caylobolide A).
Aim 2 will exploit CD methods for stereochemical elucidation of chlorocyclopropane-containing macrolides, such as that found in callipeltosides A-C and the new analogs, phorbasides A-E, at sub-nanomole levels.
AIM 3 will apply a hybrid approach to elucidate multiple contiguous stereocenters in acyclic amino-polyols and polyols using a combination of J- based analysis, semi-synthesis and 'universal NMR database' motifs for configurational analysis of two acyclic polyketide families, represented by zwittermicin A and saggitamide A, and Aim 4 will address apply the methods to isolation of novel proapoptotic compounds from marine invertebrates. The outcome of this work will provide new antitumor compound leads, resolve stereochemical complexity of key NP's, refine analytical tools for stereochemical correlations of specific classes of natural products at sub-nanomole levels, and reveal to the community new stereo-defined antitumor NP targets for total synthesis. ? ? ?
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