Modern Methods of Monosaccharide Synthesis from Non-Carbohydrate Sources.

The dioxygenase-catalysed formation of vicinal cis-diols

This tutorial review provides a survey of syntheses in which an enzymatic step contributed to generating downstream molecular complexity in the target. The first part provides a guide to the types of enzymatic transformations suitable for incorporation into synthetic schemes. The principles of symmetry, especially the concept of “latent symmetry”, which are often used to simplify enantiodivergent design of targets, are discussed next. The examples are discussed in the order of a degree of experimental difficulty associated with the execution of a particular biological technique. Lipase resolutions and desymmetrizations are discussed first followed by more advanced protocols involving oxidoreductase enzymes and ending with examples of syntheses that employ pathway engineering and directed evolution of proteins. Future prospects of biocatalytic methods as means of efficient preparation of target compounds are indicated. The authors hope that the review will serve to convince those synthetic chemists reluctant to use biological methods to include enzymatic procedures in their design.

Applications of biotransformations and biocatalysis to complexity generation in organic synthesis.

Biocatalytic approaches have yielded efficient total syntheses of the major Amaryllidaceae alkaloids, all based on the key enzymatic dioxygenation of suitable aromatic precursors. This paper discusses the logic of general synthetic design for lycoricidine, narciclasine, pancratistatin, and 7-deoxypancratistatin. Experimental details are provided for the recently accomplished syntheses of narciclasine, ent-7-deoxypancratistatin, and 10b-epi-deoxypancratistatin via a new and selective opening of a cyclic sulfate over aziridines followed by aza-Payne rearrangement. The structural core of 7-deoxypancratistatin has also been degraded to a series of intermediates in which the amino inositol unit is cleaved and deoxygenated in a homologous fashion. These truncated derivatives and the compounds from the synthesis of the unnatural derivatives have been tested against six important human cancer cell lines in an effort to further develop the understanding of the mode of action for the most active congener in this group, pancratistatin. The results of the biological activity testing as well as experimental, spectral, and analytical data are provided in this manuscript for all relevant compounds.

Total synthesis and biological evaluation of Amaryllidaceae alkaloids: narciclasine, ent-7-deoxypancratistatin, regioisomer of 7-deoxypancratistatin, 10b-epi-deoxypancratistatin, and truncated derivatives.

The Balz-Schiemann synthesis of aryl fluorides via the thermal decomposition of aryl diazonium tetrafluoroborate salts represents both the earliest and the most proverbial example of the BF4 ion as a nucleophilic fluoride source. Mechanistic studies of the Balz-Schiemann reaction have accrued strong experimental support for an SN1 mechanism via the intermediacy of an aryl cation, which is quenched by fluoride transfer directly from the BF4 ion. A notable advance in this area has been the development by Ohmori and co-workers of a fluorinative variant of the Mitsunobu reaction, involving the electrooxidative generation and subsequent thermal decomposition of alkoxytriphenylphosphonium tetrafluoroborates, allowing for the conversion of alcohols to the corresponding alkyl fluorides with inversion of configuration. Although stereoselectivity during C-F bond formation for reactions proceeding via (putative) carbocation intermediates can be highly variable, the ring-opening of strained rings or ?iranium intermediates via fluoride transfer from fluoroborate ions typically proceeds with high stereoselectivity.

Beyond the Balz-Schiemann reaction: the utility of tetrafluoroborates and boron trifluoride as nucleophilic fluoride sources.

An approach to several conduritols, both naturally occurring and unnatural derivatives, is described. The key strategy of this potentially exhaustive approach relies on the bio-oxidation of chloro- or bromobenzene to their corresponding cis-diols. Subsequent synthetic manipulations enjoy extensive use of symmetry considerations in the introduction of functionalities. Complete stereo- and enantio-control is achieved in the preparation of conduritols E 5 and F 6, aminoconduritols A-1 7 and F-4 9, fluorodeoxyconduritol F 13, chlorodeoxyconduritol F 14, and deoxyconduritol E 15. A detailed discussion of the stereoelectronic parameters that control opening of epoxy alkenes of type 33 or 37 is advanced. Full experimental details are provided for all compounds.

Biocatalysis as the strategy of choice in the exhaustive enantiomerically controlled synthesis of conduritols

Bacterial oxygenation of halogenated aromatic compounds yields arene cis-diols of type 2 of high enantiomeric purity. Further oxygenation of these extremely versatile synthetic intermediates provides for stereo- and regioselective introduction of additional functionalities such as hydroxyl groups. Several rational methods of oxygenation (epoxidation, osmylation, singlet oxygen addition, and ozonolysis) are used to produce, in short synthetic routes, cyclitol derivatives of medicinal importance. Proper symmetry considerations lead to the development of enantiodivergent synthetic design of target compounds from a single enantiomer of a starting diol. These principles are illustrated on the short syntheses of (+)- and (-)-pinitol. Stereocontrolled oxidative transformation of diols of type 2 are exemplified in the synthesis of conduritol C and dihydroconduritol C. Full experimental details are provided for all compounds. A guide to the stereorational design of any stereoisomer of cyclohexane (poly)ols or carbohydrates is provided at the end of the paper.

Biocatalysis as a Rational Approach to Enantiodivergent Synthesis of Highly Oxygenated Compounds: (+)‐ and (—)‐Pinitol and Other Cyclitols

Microbial Oxidation of Chloroaromatics in the Enantiocontrolled Synthesis of Cyclitols: (-)-Dihydroconduritol C

Preliminary investigation of the resolution potential of baker's yeast reduction of β-keto amides has been carried out with 1-phenylethylamine. Enantiomeric excess was determined by direct comparison of resolved enantiomers with derivatives prepared from commercially available (R)-(+)-1-phenylethylamine and was found to be 56–58.6% for the S enantiomer and 76–84.6% for the R enantiomer.

Homochiral amine synthesis by baker's yeast resolution of a β-keto amide: 1-Phenylethylamine

Biocatalysis as a Rational Approach to Enantiodivergent Synthesis of Highly Oxygenated Compounds: (+)- and (-)-Pinitol and Other Cyclitols.

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