Synthesis of (R)-(+)-tanikolide through stereospecific C-H insertion reaction of dichlorocarbene with optically active secondary alcohol derivatives

Asymmetric Carbene Transfer: Enhancing Chemical Diversity for Drug Discovery

The quest to explore chemical space is vital for identifying novel disease targets, impacting both the effectiveness and safety profile of therapeutic agents. The tangible chemical space, currently estimated at a conservative 108 synthesized compounds, pales in comparison to the theoretically conceivable diversity of 1060 molecules. To bridge this vast gap, organic chemists are spearheading innovative methodologies that promise to broaden this limited chemical diversity. A beacon of this progressive wave is Asymmetric Carbene Transfer (ACT), a burgeoning strategy that significantly boosts molecular diversity with efficient bond-formation and precise chiral control. This review focuses on the capabilities of ACT in creating pharmaceutically significant molecules, encompassing an array of natural products and bioactive compounds. Through the lens of ACT, we discern its substantial influence on drug discovery, paving the way for novel therapeutic avenues by expanding the boundaries of molecular diversity. This review will shed light on prospective methodological developments of ACT and articulate their conceivable contributions to the medicinal chemistry arena.

Enantioselective vinylogous Mukaiyama aldol reaction of α-ketoesters under bifunctional organocatalysis

A highly enantioselective vinylogous Mukaiyama aldol reaction to ketoesters catalysed by a hydrogen-bond-donor-based bifunctional organocatalyst is presented. The addition of silyloxy dienol ether gives rise to multifunctional chiral tertiary alcohols bearing a versatile α,β-unsaturated aldehyde with excellent enantiocontrol.

Yarrowia lipolytica as an emerging biotechnological chassis for functional sugars biosynthesis

Functional sugars have unique structural and physiological characteristics with applied perspectives for modern biomedical and biotechnological sectors, such as biomedicine, pharmaceutical, cosmeceuticals, green chemistry, and agro-food. They can also be used as starting matrices to produce biologically active metabolites of interests. Though numerous chemical synthesis routes have been proposed and deployed for the synthesis of rare sugars, however, many of them are limited and economically incompetent because of expensive raw starting feedstocks. Whereas, the biosynthesis by enzymatic means are often associated with high catalyst costs and low space-time yields. Microbial production of rare sugars via green routes using bio-renewable resources offers noteworthy solutions to overcome the aforementioned limitations of synthetic and enzymatic synthesis routes. From the microbial-based synthesis perspective, the lipogenic yeast Yarrowia lipolytica is rapidly evolving as the most prevalent and unique "non-model organism" in the bio-production arena. Due to high flux tendency through the tri-carboxylic acid cycle intermediates and precursors such as acetyl-CoA and malonyl-CoA, this yeast has been widely investigated to meet the increasing demand of industrially relevant fine chemicals, including functional sugars. Incredible interest in Y. lipolytica originates from its robust tolerance to unstable pH, salt levels, and organic compounds, which subsequently enable easy bioprocess optimization. Meaningfully, GRAS (generally recognized as safe) status creates Y. lipolytica as an attractive and environmentally friendly microbial host for the manufacturing of nutraceuticals, fermented food, and dietary supplements. In this review, we highlight the recent and state-of-the-art research progress on Y. lipolytica as a host to synthesize bio-based compounds of interest beyond the realm of well-known fatty acid production. The unique physicochemical properties, biotechnological applications, and biosynthesis of an array of value-added functional sugars including erythritol, threitol, fructooligosaccharides, galactooligosaccharides, isomalto-oligosaccharides, isomaltulose, trehalose, erythrulose, xylitol, and mannitol using sustainable carbon sources are thoroughly vetted. Finally, we conclude with perspectives that would be helpful to engineer Y. lipolytica in greening the twenty-first century biomedical and biotechnological sectors of the modern world.

Identification and characterization of EYD1, encoding an erythritol dehydrogenase in Yarrowia lipolytica and its application to bioconvert erythritol into erythrulose

In this study, gene YALI0F01650g has been isolated and characterized. Several experimental evidences suggest that the identified gene, renamed EYD1, encodes an erythritol dehydrogenase. An efficient bioreactor process for the bioconversion of erythritol into erythrulose was also developed. Using constitutive expression of EYD1 in a Y. lipolytica mutant containing a disrupted EYK1 gene, which encodes erythrulose kinase, erythrulose could be synthesized from erythritol at a rate of 0.116g/g_DCW.h and with a bioconversion yield of 0.64g/g.

Chemical compounds toxic to invertebrates isolated from marine cyanobacteria of potential relevance to the agricultural industry

In spite of advances in invertebrate pest management, the agricultural industry is suffering from impeded pest control exacerbated by global climate changes that have altered rain patterns to favour opportunistic breeding. Thus, novel naturally derived chemical compounds toxic to both terrestrial and aquatic invertebrates are of interest, as potential pesticides. In this regard, marine cyanobacterium-derived metabolites that are toxic to both terrestrial and aquatic invertebrates continue to be a promising, but neglected, source of potential pesticides. A PubMed query combined with hand-curation of the information from retrieved articles allowed for the identification of 36 cyanobacteria-derived chemical compounds experimentally confirmed as being toxic to invertebrates. These compounds are discussed in this review.

Enantioselective Synthesis of Antiepileptic Drug: (-)-Levetiracetam—Synthetic Applications of the Versatile New ChiralN-Sulfinimine

We report an asymmetric synthesis of (-)-Levetiracetam (1) in six steps starting from versatile new chiralN-sulfinimine (3). The key step, stereoselective 1,2-addition of ethylmagnesium bromide (EtMgBr) to chiralN-sulfinimine derived from (R)-glyceraldehyde acetonide and (S)-t-BSA, gave the corresponding sulfonamide (2) in high diastereoselectivity. Simultaneous deprotection and deacetylation followed by NaIO4cleavage and reduction gaveβ-amino alcohol (6). Subsequent reactions yielded the targeted compound levetiracetam (1).

Structural and synthetic investigations of tanikolide dimer, a SIRT2 selective inhibitor, and tanikolide seco-acid from the Madagascar marine cyanobacterium Lyngbya majuscula

Tanikolide seco-acid 2 and tanikolide dimer 3, the latter a novel and selective SIRT2 inhibitor, were isolated from the Madagascar marine cyanobacterium Lyngbya majuscula. The structure of 2, isolated as the pure R enantiomer, was elucidated by X-ray experiment in conjunction with NMR and optical rotation data, whereas the depside molecular structure of 3 was initially thought to be a meso compound as established by NMR, MS, and chiral HPLC analyses. Subsequent total synthesis of the three tanikolide dimer stereoisomers 4, 5, and ent-5, followed by chiral GC-MS comparisons with the natural product, showed it to be exclusively the R,R-isomer 5. Tanikolide dimer 3 (= 5) inhibited SIRT2 with an IC(50) = 176 nM in one assay format and 2.4 microM in another. Stereochemical determination of symmetrical dimers such as compound 3 pose intriguing and subtle questions in structure elucidation and, as shown in the current work, are perhaps best answered in conjunction with total synthesis.

The carbene reactivity surface: a classification

A new two-dimensional classification of singlet carbenes based on the difference in reactivity of their insertion reactions into the C-H bonds of acetonitrile and isobutane is presented. This classification combines the stability and the philicity of divalent species. Until now all of the experimentally based philicity scales are based on the addition to alkenes. Moreover, a new terminology for describing the reactivity of carbenes is introduced. Among the alkyl carbenes, acetyl carbene (2) and cyclopentadienylidene are shown as highly reactive electrophilic carbenes, whereas the other alkylidenes and alkenylidenes investigated are all less active than 2 and more nucleophilic. The stabilized-nucleophilic bicyclo[2.1.1]hex-2-en-5-ylidene (13) possesses a stability similar to that of cyclic alkyl amino carbene (CAAC) 18 and aminophosphoniocarbene 7. Strong hydrogen bridging is found between a C-H bond of acetonitrile and the nucleophilic carbenes 13 and 14.

Dihalocarbene insertion reactions into C-H bonds of compounds containing small rings: mechanisms and regio- and stereoselectivities

Novel insertion reactions of dichloro- and dibromocarbene into carbon-hydrogen bonds adjacent to cyclopropane rings are reported. It is found that the predominant isomers formed in the reactions with bicyclo[4.1.0]heptane result from insertion into the endo carbon-hydrogen bonds alpha to the three-membered ring. In the reactions of bicyclo[3.1.0]hexane, however, the exo dihalocarbene insertion products are formed as the major isomers. In some compounds cyclopropane rings "activate" adjacent carbon-hydrogen bonds, whereas other systems containing three-membered rings do not. Moreover, the influence of various substituents (methyl, geminal dimethyl, phenyl, methoxy, and ethoxy) attached to bicyclo[3.1.0]hexane and bicyclo[4.1.0]heptane in dihalocarbene reactions has been studied. The findings can be explained by the concept of maximum orbital overlaps of Walsh orbitals of the cyclopropane rings and the alpha carbon-hydrogen bonds. In stark contrast, selective insertion into the tertiary carbon-hydrogen bonds of the cyclobutane ring in bicyclo[4.2.0]octane is observed.

Facile and efficient synthesis of lactols by a domino reaction of 2,3-epoxy alcohols with a hypervalent iodine(III) reagent and its application to the synthesis of lactones and the asymmetric synthesis of (+)-tanikolide

The domino reaction of 2,3-epoxy-1-alcohol derivatives, namely tetrasubstituted 2,3-epoxy-1-alcohols and 2- or 3-alkyl trisubstituted 2,3-epoxy-1-alcohols, with PhI(OCOCF(3))(2) in the presence of H(2)O is described in detail. In this reaction, several types of lactol derivatives can be directly obtained from the 2,3-epoxy-1-alcohol derivatives in a single operation. The obtained lactols were successively converted into the corresponding lactones. This reaction is applicable to the construction of optically active lactone compounds. The asymmetric total synthesis of (+)-tanikolide, an antifungal marine natural product, has been effectively achieved by using this reaction.

Diastereoselective aldol reactions with butane-2,3-diacetal protected glyceraldehyde derivatives

Diastereoselective aldol coupling reactions with butane-2,3-diacetal (BDA) protected glyceraldehyde derivatives are reported. Good selectivities of up to 20:1 for the homologated aldol products have been achieved in preparatively useful yields.

Marine natural products: synthetic aspects

An overview of marine natural products synthesis during 2004 is provided. As with the previous installment of this series, the emphasis is on total syntheses of molecules of contemporary interest, new total syntheses, and syntheses that have resulted in structure confirmation or stereochemical assignments.