Synthesis of the C(1)C(16) fragment of bryostatins

Advances in the synthesis of glycosidic macrolides: clavosolides A-D and cyanolide A

Covering: 2005 to 2016Clavosolides A-D and cyanolide A are glycosidic macrolides and represent a new family of marine natural products. They possess a number of unusual structural features and have attracted considerable interest from the synthetic community. This review presents a comprehensive survey of all aspects of the clavosolides A-D and cyanolide A. Specific topics include isolation, structure determination, biological activity, and synthetic approaches.

Recent efforts to construct the B-ring of bryostatins

Among macrocyclic natural products, bryostatins have excellent bioactivities and unique structures that make them highly attractive to synthetic chemists. Particularly challenging for the total synthesis of bryostatins is the B-ring, which features a cis-tetrahydropyran containing a geometrically defined exocyclic Z-methyl enoate. Synthetic chemists have recently displayed great prowess in their efforts to construct this ring, and here we summarize the progress towards this goal.

Atom-economic and stereoselective syntheses of the ring a and B subunits of the bryostatins

This article describes chemoselective and atom-economic methods for the stereoselective assembly of the ring A and B subunits of bryostatins. A Ru-catalyzed tandem alkene-alkyne coupling/Michael addition reaction was developed and applied to the synthesis of bryostatin ring B. We explored an acetylide-mediated epoxide-opening/6-exo-dig cyclization route to access the bryostatin ring A, although ring A was eventually furnished through an acid-catalyzed tandem transketalization/ketalization sequence. In addition, a dinuclear zinc-catalyzed methyl vinyl ketone (MVK) aldol strategy was evaluated for the construction of the polyacetate moiety. Utilization of these methods ultimately led to the rapid assembly of the northern bryostatin fragment containing both the ring A and B subunits.

The medicinal potential of promising marine macrolides with anticancer activity

Marine natural products have become a major source of new chemical entities in the discovery of potential anticancer agents that potently suppress various molecular targets. In particular, the marine macrolides, which include an array of novel biomolecules endowed with outstanding cytotoxic and/or antiproliferative activities, are a prominent class of marine natural products that offer continued promise for breakthroughs in anticancer research. Herein we highlight some recent studies of promising marine macrolides, paying particular attention to their discovery, anticancer activities, mechanisms of action, chemical synthesis, and representative analogues.

New approaches to the total synthesis of the bryostatin antitumor macrolides

In this Focus Review, we give an overview of various bryostatin total syntheses. We also discuss the synthesis of various bryostatin analogues and their biological activity. Work reviewed includes that of Masamune, Evans, Nishiyama and Yamamura, Hale and Manaviazar, Trost, Wender, Keck, Burke, Thomas, and Krische. Our coverage is primarily for the period 2001-2009, since detailed reviews already exist on bryostatin total synthesis work and biology up to this time.

Total synthesis of spirotenuipesines A and B

Spirotenuipesines A and B, isolated from the entomopathogenic fungus Paecilomyces tenuipes by Oshima and co-workers, have been synthesized. The synthesis features the highly stereoselective construction of two vicinal all-carbon quaternary centers (C(5) and C(6)) via an intramolecular cyclopropanation/radical initiated fragmentation sequence and a diastereoselective intermolecular Diels-Alder reaction between alpha-methylenelactone dienophile 20 and synergistic diene 6a. Installation of the C(9) tertiary alcohol occurred via nucleophilic methylation. An RCM reaction to produce a tetrasubstituted double bond in the presence of free allylic alcohol and homoallylic oxygenated functional group is also described. This route shortened the synthesis of 11 from 9 steps to 3 steps. We have further developed a strategy to gain access to optically active spirotenuipesines A and B through the synthesis of enantioenriched 10 from commercially available R-(-)-epichlorohydrin.

Intramolecular ene reaction of epoxyallylsilanes: synthesis of allyl- and vinylsilane-functionalized cyclohexanols

[reaction: see text] Epoxyallylsilanes bearing the bulky tert-butyldiphenylsilyl group undergo an uncommon tandem rearrangement-cyclization process upon treatment with Lewis acids. Two pathways for the carbonyl ene reaction are observed: one leading to allylsilane-cyclohexanols when the epoxyallylsilane (28-31) is nonsubstituted, 2-, or 4-monosubstituted and other leading to vinylsilane-cyclohexanols when the epoxyallylsilane (24-27) is 2,4-disubstituted or trisubstituted. An explanation for the observed regio- and stereoselectivity is advanced and a reliable mechanism proposed.

Stereoselective construction of cis-2,6-disubstituted tetrahydropyrans via an intramolecular bismuth-mediated oxa-conjugate addition reaction

The intramolecular oxa-conjugate addition of tethered triethylsilyloxy substituted alpha,beta-unsaturated ketones mediated by bismuth(III) nitrate pentahydrate provides a mild and efficient method for the stereoselective construction of cis-2,6-disubstituted tetrahydropyrans.