Delbert L. Herald

Studies directed towards the refinement of the pancratistatin cytotoxic pharmacophore.

Two deoxy-analogues of the anticancer/antiviral agent pancratistatin containing functionality complementary to the minimum structural pharmacophore were synthesized and subjected to anticancer screening. One of the analogues exhibited selective inhibition of certain tumor cell lines but was significantly less potent than the natural products. The minimum structural pharmacophore has now been refined from eight to three possible structures.

Conformational analysis of a marine antineoplastic macrolide, bryostatin 10☆

Abstract Conformation of bryostatin 10, a marine antineoplastic macrolide, in CDCl3 was analyzed by the spectroscopic and computational chemical methods. A combination of homonuclear two-dimensional NMR techniques at 600 MHz have enabled us to perform complete assignment of the 1H signals of bryostatin 10 in CDCl3. The conformation of its solution form was elucidated by a phase sensitive ROESY spectrum, temperature effect on OH proton and 3J vicinal coupling constants. Restrained molecular-dynamics simulation led to a well defined conformation of the compound in solution, which was found to be homologous to that of bryostatin 2 observed in the solid state.

Dolastatins 24: synthesis of (–)-dolastatin 10. X-Ray molecular structure of N,N-dimethylvalyl-valyl-dolaisoleuine tert-butyl ester

Total synthesis of the extraordinary antineoplastic constituent, dolastatin 10, from the Indian Ocean mollusc Dolabella auricularia has been summarized. The final synthetic step involved diethyl cyanophosphonate-mediated coupling of Dov-Val-Dil with Dap-Doe. Improved syntheses of these important precursors has led to a very practical synthesis of natural dolastatin 10. Important details of the HPLC and high-field (500 MHz) NMR characterization techniques employed to confirm the purity of dolastatin 10 have been recorded.

Isolation and X-ray crystal structure of racemic xestospongin D from the Singapore marine sponge Niphates SP1

Abstract (±)-Xestospongin D (2) has been isolated from the Singapore marine sponge Niphates sp . The natural product was found to be racemic in contrast to earlier isolations of (+)-xestospongin D from Xestospongia and Haliclona species. The (±)-xestospongin D was found to inhibit growth of certain human cancer cell lines comprising the NCI panel ( e.g. , leukemia subpanel, mean GI 50 3.62 ± 2.02 × 10 −6 M; breast subpanel, mean GI 50 4.53 ± 1.98 × 10 −6 M) as well as the murine P388 lymphocytic leukemia (ED 50 1.7 μg/mL) and the bacterium Micrococcus luteus .

Antineoplastic agents 470. Absolute configuration of the marine sponge bromopyrrole agelastatin A

Two bromopyrrole marine alkaloids were isolated from the Mexican sponge, Agelas sp.: hymenidin (1) and agelastatin A (2). The structures were elucidated by analysis of their spectroscopic data and found to correspond to those in the literature. The absolute configuration of agelastatin A (2) was elucidated by single-crystal X-ray diffraction methods. Agelastatin A (2) exhibited strong activity against a panel of human cancer cell lines as well as human umbilical vein endothelial cells.

The Dolastatins 20. A Convenient Synthetic Route to Dolastatin 15

Abstract A segment synthetic strategy was utilized for obtaining the Dolabella auricularia (Indian Ocean sea hare) depsipeptide dolastatin 15. Reaction of protected (S)-Hiva-(S)-Phe 2c with isopropenyl chloroformate followed by Meldrums ester, cyclization (2c → 3a) of the product in toluene and finally methylation afforded the key (S)-dolapyrrolidine (Dpy) derivative 3b. Condensation of tripeptide 8 with the three unit Dpy segment 5b followed by deprotection and coupling (diethyl phosphorocyanidate) led to dolastatin 15 in 11% overall yield. The powerful and selective activity of dolastatin 15 against the U.S. National Cancer Institutes panel of human cell lines has been summarized.

Antineoplastic agents. 558. Ampelocissus sp. cancer cell growth inhibitory constituents

An investigation of the Phillippine Ampelocissus sp. roots for cancer cell growth inhibitory components led to the isolation of a new acetogenin characterized as 22-epicalamistrin (1) employing primarily 2D NMR and high-resolution mass spectral analysis. Two other antineoplastic constituents proved to be the known acetogenin uvaribonin (2) and chalcone 3. Constituents 1-3 were all found to show significant cancer cell growth inhibitory activity against a panel of human cancer cell lines.

Antineoplastic Agents. 511. Direct Phosphorylation of Phenpanstatin and Pancratistatin

Selective phosphorylation of phenpanstatin (3a) with tetrabutylammonium dihydrogen phosphate and dicyclohexylcarbodiimide in pyridine followed by cation-exchange chromatographic procedures was found to provide an efficient route to a new series (3b-3d) of promising 3,4-O-cyclic phosphate prodrugs designated phenpanstatin phosphates. Application of analogous reaction conditions to pancratistatin (1a) led to a mixture of monophosphate derivatives where sodium pancratistatin 4-O-phosphate (4a) was isolated and the structure confirmed by X-ray crystallography. Modification of the reaction conditions allowed direct phosphorylation of pancratistatin followed by cation-exchange chromatography to afford sodium pancratistatin 3,4-O-cyclic phosphate (5a), which was selected for preclinical development.

Antineoplastic Agents. 570. Isolation and Structure Elucidation of Bacillistatins 1 and 2 from a Marine Bacillus silvestris

Two new cyclodepsipeptides designated bacillistatins 1 (1) and 2 (2) have been isolated from cultures of a sample of Bacillus silvestris that was obtained from a Pacific Ocean (southern Chile) crab. Each 12-unit cyclodepsipeptide strongly inhibited growth of a human cancer cell line panel, with GI(50)s of 10(-4)-10(-5) microg/mL, and each compound was active against antibiotic-resistant Streptococcus pneumoniae. The structures were elucidated by a combination of X-ray diffraction and mass and 2D NMR spectroscopic analyses, together with chemical degradation.

Antineoplastic agents. 556. Isolation and structure of Coprinastatin 1 from Coprinus cinereus.

Cancer cell line bioassay-guided separation of an ethyl acetate extract prepared from a plant-associated fungus, Coprinus cinereus, led to the isolation of three new sesquiterpenes, coprinastatin 1 (1), coprinol (2), and the epimer (4a), of the known sesquiterpene triol (4b). The previously described sesquiterpene 3 and oxazolinone 5 were also isolated. The structure and relative configuration of coprinastatin 1 (1) were determined by HRMS and by 1D- and 2D-NMR spectroscopic analyses. The structure of terpene 2 was elucidated by single-crystal X-ray diffraction experiments. The remaining structures were similarly determined, structure 3 by spectroscopic analyses and both 4a and 5 by X-ray crystal structure determination. Coprinastatin 1 (1) was found to inhibit growth of the murine P388 lymphocytic leukemia cell line and the pathogenic bacterium Neisseria gonorrhoeae.