Convergent total synthesis of (+)-mycalamide A

Mukaiyama Aldol Reactions in Aqueous Media

Mukaiyama aldol reactions in aqueous media have been surveyed. While the original Mukaiyama aldol reactions entailed stoichiometric use of Lewis acids in organic solvents under strictly anhydrous conditions, Mukaiyama aldol reactions in aqueous media are not only suitable for green sustainable chemistry but are found to produce singular phenomena. These findings led to the discovery of a series of water-compatible Lewis acids such as lanthanide triflates in 1991. Our understanding on these beneficial effects in the presence of water will be deepened through the brilliant examples collected in this review. 1 Introduction 2 Rate Enhancement by Water in the Mukaiyama Aldol Reaction 3 Lewis Acid Catalysis in Aqueous or Organic Solvents 3.1 Water-Compatible Lewis Acids 4 Lewis-Base Catalysis in Aqueous or Organic Solvents 5 The Mukaiyama Aldol Reactions in 100% Water 6 Asymmetric Catalysts in Aqueous Media and Water 7 Conclusions and Perspective.

Isolation, biological activity, synthesis, and medicinal chemistry of the pederin/mycalamide family of natural products

This review highlights the broad range of science that has arisen from the isolation of pederin, the mycalamides, theopederins, and onnamides, and psymberin. Specific topics include structure determination, biological activity, synthesis, and analog preparation and analysis.

The protein synthesis inhibitors mycalamides A and E have limited susceptibility toward the drug efflux network

The mycalamides belong to a family of protein synthesis inhibitors noted for antifungal, antitumour, antiviral, immunosuppressive, and nematocidal activities. Here we report a systematic analysis of the role of drug efflux pumps in mycalamide resistance and the first isolation of mycalamide E. In human cell lines, neither P-glycoprotein overexpression nor the use of efflux pump inhibitors significantly modulated mycalamide A toxicity in the systems tested. In Saccharomyces cerevisiae, it appears that mycalamide A is subject to efflux by the principle mediator of xenobiotic efflux, Pdr5p along with the major facilitator superfamily pump Tpo1p. Mycalamide E showed a similar efflux profile. These results suggest that future drugs based on the mycalamides are likely to be valuable in situations where efflux pump-based resistance leads to failure of other chemotherapeutic approaches, although efflux may be a mediator of resistance in antifungal applications.

Total synthesis and biological evaluation of pederin, psymberin, and highly potent analogs

The potent cytotoxins pederin and psymberin have been prepared through concise synthetic routes (10 and 14 steps in the longest linear sequences, respectively) that proceed via a late-stage multicomponent approach to construct the N-acyl aminal linkages. This route allowed for the facile preparation of a number of analogs that were designed to explore the importance of the alkoxy group in the N-acyl aminal and functional groups in the two major subunits on biological activity. These analogs, including a pederin/psymberin chimera, were analyzed for their growth inhibitory effects, revealing several new potent cytotoxins and leading to postulates regarding the molecular conformational and hydrogen bonding patterns that are required for biological activity. Second generation analogs have been prepared based on the results of the initial assays and a structure-based model for the binding of these compounds to the ribosome. The growth inhibitory properties of these compounds are reported. These studies show the profound role that organic chemistry in general and specifically late-stage multicomponent reactions can play in the development of unique and potent effectors for biological responses.

Microtubule-stabilizing drugs from marine sponges: focus on peloruside A and zampanolide

Marine sponges are an excellent source of bioactive secondary metabolites with potential therapeutic value in the treatment of diseases. One group of compounds of particular interest is the microtubule-stabilizing agents, the most well-known compound of this group being paclitaxel (Taxol), an anti-cancer compound isolated from the bark and leaves of the Pacific yew tree. This review focuses on two of the more recent additions to this important class of drugs, peloruside A and zampanolide, both isolated from marine sponges. Peloruside A was isolated from Mycale hentscheli collected in New Zealand coastal waters, and it already shows promising anti-cancer activity. Two other potent bioactive compounds with different modes of action but isolated from the same sponge, mycalamide A and pateamine, will also be discussed. The fourth compound, zampanolide, most recently isolated from the Tongan sponge Cacospongia mycofijiensis, has only recently been added to the microtubule-stabilizing group of compounds, and further work is in progress to determine its activity profile relative to peloruside A and other drugs of this class.

Total synthesis of irciniastatin A (Psymberin)

The total synthesis of (+)-iriciniastatin A (psymberin) is reported in 19 steps and 6% overall yield. Key reactions include a highly convergent enolsilane-oxocarbenium ion union to generate the C8-C25 fragment and a late-stage coupling of a hemiaminal and acid chloride to complete the synthesis.

Total synthesis of theopederin D

The total synthesis of the potent cytotoxin theopederin D has been achieved through the use of an oxidative carbon–carbon bond cleavage reaction to form an acyliminium ion in the presence of acid labile acetal groups Other key transformations include an acid mediated functionalization of a tetrahydrofuranyl alcohol in the presence of a tetrahydropyranyl alcohol, a syn -selective glycal epoxide opening, and a catalytic asymmetric aldehyde-acid chloride condensation.

The Mitsunobu Reaction: Origin, Mechanism, Improvements, and Applications

The Mitsunobu reaction is a widely used and versatile method for the dehydrative oxidation-reduction condensation of an acid/pronucleophile usually with a primary or secondary alcohol that requires the combination of a reducing phosphine reagent together with an oxidizing azo reagent. The utility of this reaction stems from the fact that it is generally highly stereoselective and occurs with inversion of the stereochemical configuration of the alcohol starting material. Furthermore, as carboxylic acids, phenols, imides, sulfonamides, and other compounds can be used as the acid/pronucleophile, this reaction is useful for the preparation of a wide variety of functional groups. This Focus Review of the Mitsunobu reaction summarizes its origins, the current understanding of its mechanism, and recent improvements and applications.

Chemical Markup, XML, and the World Wide Web. 7. CMLSpect, an XML vocabulary for spectral data

CMLSpect is an extension of Chemical Markup Language (CML) for managing spectral and other analytical data. It is designed to be flexible enough to contain a wide variety of spectral data. The paper describes the CMLElements used and gives practical examples for common types of spectra. In addition it demonstrates how different views of the data can be expressed and what problems still exist.