Stereoselective synthesis of (1R)- and (1R,2S)-1-aryl-2-alkylamino alcohols from (R)-cyanohydrins

Polyfunctionalized organoselenides: New synthetic approach from selenium-containing cyanohydrins and anti-melanoma activity

A series of seleno-containing polyfunctionalized compounds was synthesized exploring cyanohydrin chemistry, including α-hydroxy esters, α-hydroxy acids, 1,2-diols, and 1,2-diacetates, with yields ranging from 26 up to 99 %. The cytotoxicity of all synthesized compounds was then evaluated using a non-tumor cell line (BALB/3T3 murine fibroblasts), and those deemed non-cytotoxic had their anti-melanoma activity evaluated using B16-F10 murine melanoma cells. These assays identified two compounds with selective cytotoxic activity against the tested melanoma cell line, showing a potential anti-melanoma application.

1-Ethyl-3-methylimidazolium acetate as a highly efficient organocatalyst for cyanosilylation of carbonyl compounds with trimethylsilyl cyanide

1-Ethyl-3-methylimidazolium acetate is introduced as a robust organocatalyst for solvent-free cyanosilylation of carbonyl compounds with trimethylsilyl cyanide (TMSCN). The catalyst loading can be reduced to as low as 0.1–0.0001 mol % under mild reaction conditions, giving considerably high TOF values from 10,843 h⁻¹ to 10,602,410 h⁻¹ in the field of organocatalyzed transformations. The present protocol not only tolerates with extensive carbonyl compounds but also provides somewhat insight into the mechanism of ionic liquids (ILs)-catalyzed reactions.

Carbon dioxide as a carbonylating agent in the synthesis of 2-oxazolidinones, 2-oxazinones, and cyclic ureas: scope and limitations

Carbon dioxide can be used as a convenient carbonylating agent in the synthesis of 2-oxazolidinones, 2-oxazinones, and cyclic ureas. The transient carbamate anion generated by treating a primary or secondary amine group in basic media can be activated with phosphorylating agents such as Diphenylphosphoryl azide (DPPA) and Diphenyl chlorophosphate (DPPCl) but also with other types of electrophiles such as SOCl(2), TsCl, or AcCl. The intramolecular trapping of the activated carbamate by a hydroxyl group leads to the formation of 2-oxazolidinones or 2-oxazinones in good to excellent yields. This methodology was successfully applied to the synthesis of cyclic ureas up to 7-membered rings from the corresponding diamines.

Potential and capabilities of hydroxynitrile lyases as biocatalysts in the chemical industry

The application of hydroxynitrile lyases (HNLs) as catalysts for the stereoselective condensation of HCN with carbonyl compounds has been reported as early as 1908. This enzymatic C-C bond coupling reaction furnishes enantiopure cyanohydrins which serve as versatile bifunctional building blocks for chemical synthesis. Screening of natural sources led to the discovery of both (R)- and (S)-selective HNLs, and several distinctly different classes of these enzymes with substantial differences concerning sequence, structure, and mechanism have been found. Especially during the last two centuries, HNLs have been developed into valuable biocatalysts, which can be produced in recombinant form by overexpression in microbial hosts, resulting in the implementation of industrial processes utilizing these enzymes. Recently, protein engineering in combination with in silico methods gave rise to the development of a tailor-made HNL for large-scale manufacturing of a specific target cyanohydrin.

Hydroxynitrile lyases in stereoselective catalysis

(R)- as well as (S)-cyanohydrins are now easily available as a result of the excellent accessibility, the relatively high stability and the easy handling of hydroxynitrile lyases (HNLs). The optimization of reaction conditions (solvent, temperature, and using site-directed mutagenesis, etc.) has enabled HNL-catalyzed preparations of optically active cyanohydrins on a technical scale. The enantioselectivity of chiral metal-complex-catalyzed additions of trimethylsilyl cyanide to aldehydes has been improved, but is, by far, not yet competitive with the HNL-catalyzed reactions.

Enzyme mediated C-C bond formation

A number of significant biocatalysts have been investigated over the past year to improve accessibility, functional knowledge and use in developing synthetic applications. In particular, accumulating protein structural information has facilitated major advances in the detailed understanding of catalytic events and has, therefore, set the stage for rational protein engineering. This will have important implications for the future scope of practical applications, the first of which are currently being industrialized.