(+)-Phorboxazole A synthetic studies. A highly convergent, second generation total synthesis of (+)-phorboxazole A

[structure: see text] A second generation total synthesis of the potent antitumor agent (+)-phorboxazole A (1) has been achieved. The cornerstone of this approach comprises a more convergent strategy, involving late-stage Stille union of a fully elaborated C(1-28) macrocycle with a C(29-46) side chain. The second generation synthesis entails the longest linear sequence of 24 steps, with an overall yield of 4.2%.     

Design and synthesis of a potent phorboxazole C(11-15) acetal analogue

[structure: see text] We disclose here the design, synthesis, and biological evaluation of simplified Z- and E-C(2-3) alkynyl phorboxazole C(11-15) acetals (+)-7Z and (+)-7E, wherein the Z-isomer proved to be a potent nanomolar cytotoxic agent. Reevaluation of (+)-C(45-46) E-chloroalkenyl phorboxazole A (6) confirms subnanomolar activity across a broad panel of human cancer cell lines.     

A second-generation total synthesis of (+)-phorboxazole A.

A highly convergent second-generation synthesis of (+)-phorboxazole A has been achieved. Highlights of the synthetic approach include improved Petasis-Ferrier union/rearrangement conditions on a scale to assemble multigram quantities of the C(11-15) and C(22-26) cis-tetrahydropyrans inscribed with the phorboxazole architecture, a convenient method to prepare E- and Z-vinyl bromides from TMS-protected alkynes utilizing radical isomerization of Z-vinylsilanes, and a convergent late-stage Stille union to couple a fully elaborated C(1-28) macrocyclic iodide with a C(29-46) oxazole stannane side chain to establish the complete phorboxazole skeleton. The synthesis, achieved with a longest linear sequence of 24 steps, proceeded in 4.6% overall yield.     

Synthesis and biological evaluation of phorboxazole congeners leading to the discovery and preparative-scale synthesis of (+)-chlorophorboxazole a possessing picomolar human solid tumor cell growth inhibitory activity

Highly convergent syntheses of eight phorboxazole congeners and their evaluation against a diverse panel of human solid tumor cancer cell lines have been achieved. Specifically, the C(45-46) alkyne, alkene, and alkane phorboxazole A analogues [(+)-4-(+)-6] were constructed and found to display single digit nanomolar cell growth inhibitory activities in a series of human cancer cell lines. The structurally simplified C(11-15)-acetal congener (+)-20Z also proved potent albeit reduced (cf. 34.6 nM) when evaluated against the same cell line panel. Importantly, (+)-C(46)-chlorophorboxazole A (3) displayed picomolar (pM) inhibitory activity in several cell lines.     

Phorboxazole Synthetic Studies: Design, Synthesis and Biological Evaluation of Phorboxazole A and Hemi-Phorboxazole A Related Analogues

The design, synthesis and biological evaluation of a new phorboxazole analogue, comprising an acetal replacement for the C-ring tetrahdropyran of the natural product and carrying a potency-enhancing C(45-46) vinyl chloride side chain, is described. In addition, the synthesis of (+)-hemi-phorboxazole A and a series of related hemi-phorboxazole A analogues has been achieved. The new acetal ring replacement analogue displayed activity comparable to that of the parent natural product against HCT-116 (colon) cells (IC(50) 2.25 ng/mL). Equally important, the phorboxazole analogue and two related hemiphorboxazole A congeners exhibited significant antifungal activity when assayed against pathogenic Candida albicans strains.     

(+)-Phorboxazole A synthetic studies. Identification of a series of highly cytotoxic C(45-46) analogues

[structure: see text] Effective, scalable total syntheses and biological evaluation of six phorboxazole A analogues (1-6) have been achieved. Importantly, the C(45-46)-saturated, C(45-46)-alkenyl, and the C(45-46)-E-chloroalkenyl congeners (4, 5, and 6, respectively) reveal low nanomolar tumor cell growth inhibitory activity (GI50's) similar to or, in some cell lines, greater than that of the phorboxazoles across a diverse panel of human cancer cell lines.     

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.