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Abstract: The asymmetric synthesis of two well-known anti-depressant drugs, fluoxetine and duloxetine has been accomplished in a chemoenzymatic manner. The main highlight of the synthesis is the enantioselective cyanohydrin formation by a plant (R)-HNL (hydroxynitrile lyase). The enantiopure cyanohydrins are then synthetically manipulated into the above two drug molecules and two of their structural analogues, atomoxetine and nisoxetine. [Copyright &y& Elsevier]

Abstract: Using an acetone precipitation method, crude (S)-hydroxynitrile lyase [(S)-MeHNL] was separated from Munihot esculenta (cassava) leaves, and used directly as biocatalyst to catalyze asymmetric cyanohydrination and produce cyanohydrins with enantiomeric purities (⩾90% ee) significantly greater than those previously reported. The use of a water/i-Pr2O system with an enzyme, NaCN, and appropriate amounts of acetic acid is crucial in improving the stereoselectivity of cyanohydrin formation by minimizing the non-enzymatic reaction and the racemization of the chiral products. The proposed isolation method for crude (S)-MeHNL has a high value because of its simplicity, and low cost as well as the high activity of the crude (S)-MeHNL. [Copyright &y& Elsevier]

Abstract: The asymmetric addition of trimethylsilyl cyanide to aldehydes catalysed by chiral metal(salan) complexes has been investigated. Salan complexes of titanium and vanadium displayed only low catalytic activity, but a bimetallic aluminium(salan) complex gave high levels of catalytic activity and reasonable asymmetric induction when used with triphenylphosphine oxide as a cocatalyst. Mechanistic studies showed that the reactions were first order in catalyst and aldehyde concentrations, but zero order in trimethylsilyl cyanide and triphenylphosphine oxide concentrations. A Hammett analysis indicated that there was no significant change in the electron density at the aldehyde benzylic position during the rate determining step of the catalytic cycle. On the basis of the kinetic data, a catalytic cycle is proposed which accounts for the differences observed between [Al(salen)]2O and [Al(salan)]2O based catalysts. [Copyright &y& Elsevier]

Abstract: The preparation of enantiopure cyanohydrin acetates via enzymatic hydrolysis has been investigated by screening a range of biocatalysts and reaction conditions. Enzymatic resolution has been optimised through variation of the hydrolase biocatalyst and reaction conditions leading to synthetically useful routes to enantiopure cyanohydrin acetates. [Copyright &y& Elsevier]

Abstract: Oxovanadium(V) complex 4 was prepared from VOSO4 and tridentate Schiff base ligand, which was prepared from substituted salicylaldehyde and inexpensive (S)-valine. Asymmetric silylcyanation of the aldehydes catalyzed by catalyst 4 afforded cyanohydrins with good enantioselectivities. [Copyright &y& Elsevier]

Abstract: The synthesis of enantiopure unsymmetrical N-heterocyclic based zwitterions incorporating imidazolinium and alkylsulfonate or sulfamate groups is described. The desired compounds were prepared in good yields from 1,3-propanesultone or cyclic sulfamidates and imidazolines. The imidazolinium based zwitterions proved to be versatile chiral solvating agents for Mosher’s acid, alcohols, cyanohydrins, amino alcohols, nitro alcohols, thiols, and carboxylic acids with very high shifts in the 1H and 19F NMR. [Copyright &y& Elsevier]

Abstract: The enantioselective titanium(IV)-catalyzed cyanobenzoylation of aldehydes using 1:1 BINOLAM/Ti(OiPr)4 mixtures as a precatalyst gave O-aroyl cyanohydrins 4 with good enantiomeric excesses. The standard optimization set carried out on the assumption of Curtin–Hammett behavior, led to no amelioration. Extensive experimental and computational studies were carried out with the purpose of identifying the key mechanistic aspects governing enantioselectivity. HCN and isopropyl benzoate were detected in the reacting mixtures. This as well as the reaction response to the presence of an exogenous base, and the failure to react in the presence of Binol/Ti(OiPr)4 mixtures, led us to propose, not a direct but an indirect process involving an enantioselective hydrocyanation step followed by O-benzoylation. Computational work carried out with mononuclear monomeric MM and dinuclear mixed dimer DlMD as catalysts support this mechanistic proposal. On the other hand, cyanobenzoylations carried out with 1:2 or higher 1:n (up to 1:5) BINOLAM/Ti(OiPr)4 mixtures appear to involve a reversal of the enantioselection. This, together with the fact that the benzoylation of the ligated iPrOH is a slow reaction, has led us to conclude that these cyanobenzoylations do not fit within the standard Curtin–Hammett kinetic scheme. Instead, such BINOLAM/Ti(OiPr)4 -catalyzed cyanobenzoylations of aldehydes rather behave as non-Curtin–Hammett kinetic schemes. Further computational analysis is needed in order to make a clear distinction between Curtin–Hammett and non-Curtin–Hammett kinetic frameworks. [Copyright &y& Elsevier]

Abstract: The enantioselective preparation of both enantiomers of the benzo-fused cyanohydrin derived from α-tetralone via lipase catalyzed processes is described. The (S)-enantiomer has been obtained as the remaining substrate in the CAL-A catalyzed aminolysis of the methoxyacetylated derivative, using a structurally related amine as the nucleophile. The (R)-enantiomer has been obtained as the product of CAL-A or PSL-C catalyzed hydrolysis of the methoxyacetylated derivative in organic solvents. The resolutions of several structural analogs of this cyanohydrin have been also tested under similar conditions. [Copyright &y& Elsevier]

The chemoenzymatic synthesis of highly enantiopure (R)- and (S)-benzofuranyl- and benzo[b]thiophenyl-cyanohydrins and their chemical transformation into the corresponding heteroaryl-1,2-ethanediols is described. [Copyright &y& Elsevier]

Abstract: The catalyst generated in situ from Mn(OAc)2 and a chiral Schiff base ligand exhibited excellent catalytic abilities in asymmetric cyanohydrin formation from aldehydes with sodium cyanide in up to 99% enantioselectivity and good yield. [Copyright &y& Elsevier]

Abstract: Enantiomerically enriched O-methoxycarbonyl cyanohydrins were obtained using an enantioselective addition of methyl cyanoformate to aldehydes organocatalyzed by a dimeric anthracenyldimethyl-derived cinchonidine ammonium salt (1mol% catalyst loading) in the presence of substoichiometric amounts of triethylamine (20mol%). Aromatic and heteroaromatic aldehydes usually afford high enantioselectivities (up to 96%) and quantitative yields of the corresponding O-methoxycarbonyl cyanohydrins, whereas aliphatic and α,β-unsaturated aldehydes give lower enantioselectivities (up to 60%) in high yields. The observed sense of the enantioselection was always the same, and the organocatalyst was almost quantitatively recovered by ether-promoted precipitation without any loss of activity. The use of resin-supported cinchonidine-derived ammonium salts as an organocatalyst in this transformation was also explored. [Copyright &y& Elsevier]

Abstract: Herein we report the biocatalytic asymmetric synthesis of cyanohydrins by using a new (R)-HNL from Prunus armeniaca. Several sterically demanding aromatic aldehydes which have never been used as substrates for any known HNLs are employed for the new (R)-HNL from P. armeniaca. The cyanohydrins synthesized are obtained in good chemical yield with excellent enantioselectivities. [Copyright &y& Elsevier]

Abstract: Chiral trianglamines 1 and 2 were found to be useful as NMR chiral shift reagents for the determination of enantiomeric purity and absolute configuration of several kinds of secondary alcohols, cyanohydrins, and propargyl alcohols. [Copyright &y& Elsevier]

Abstract: We have developed a biocatalytic method to produce lactones and related compounds via the enzymatic hydrolysis of γ- and β-hydroxynitriles. The synthesis is a mild, general, and environmentally friendly way to enantioselectively hydrolyze nitriles with commercially available nitrilase enzymes. The synthesis of four pheromones is demonstrated via a one-step method. [Copyright &y& Elsevier]

Abstract: The synthesis of (R)- and (S)-cyanohydrins from a range of aromatic methyl and ethyl ketones, including the first examples from substituted variants of phenylacetone, benzylacetone and propiophenone, is described. Commercially available hydroxynitrile lyase (HNL) enzymes were used to catalyze the asymmetric addition of cyanide to the ketones, including the first successful application of the flax HNL (LuHNL) to the synthesis of any aromatic (S)-cyanohydrin. Both reaction yields and stereoselectivities were shown to be influenced by the carbon chain length between the ketone and phenyl functional groups, and the type of aromatic substitution present on the starting material. Substrates converted with the greatest degree of productivity and selectivity were phenylacetones with large, electron withdrawing meta-substituents, such as 3-Cl, 3-Br and 3-CF3 phenylacetones, from which cyanohydrins are formed with 93–99% ee and 61–71% yield. [Copyright &y& Elsevier]

Abstract: The asymmetric cyanobenzoylation of aldehydes has been carried out for the first time, by reaction with benzoyl cyanide in a process catalysed by either (R)- or (S)-3,3′-bis(diethylaminomethyl)-1,1′-binaphthol BINOLAM–Ti(IV) complexes at room temperature and without additives. The reaction can be described as an overall cyano-O-benzoylation of aldehydes where a Lewis acid–Brönsted base (LABB) dual role for the catalyst induced firstly the key enantioselective hydrocyanation, which is then followed by O-benzoylation furnishing enantioenriched O-benzoyl cyanohydrins. [Copyright &y& Elsevier]

Abstract: Enantiomerically pure cyanohydrins derived from 2-p-tolylsulfinyl benzaldehyde can be obtained by reaction with different hydrocyanating reagents in the presence of Yb(OTf)3 or Y(OTf)3. [Copyright &y& Elsevier]

The addition of Et2AlCN in the presence of ZnBr2 or Et2AlCl to 1,3-dicarbonyl compounds derived from (S)-4-isopropyl-2-oxazolidinone, proceeds with high diastereoselectivity (94–98% de) and good chemical yields. This type of addition to chiral β-dicarbonyl substrates represents a new synthetic methodology leading to the formation of enantiomerically pure cyanohydrins. [Copyright &y& Elsevier]

A series of novel (R)-5-phenylfuran-2-yl cyanomethyl butanoates were prepared by Pseudomonas cepacia lipase-catalysed dynamic kinetic resolution in toluene. The method exploits a basic resin both for the racemization and formation of phenylfuran-based cyanohydrins and for the decomposition of acetone cyanohydrin in one-pot with enzymatic enantioselective acylation using vinyl butanoate. The lipase-catalysed methanolysis of racemic 5-phenylfuran-2-yl cyanomethyl butanoates in toluene with E ≫100 was shown to be usable when the corresponding (S)-butanoates are needed. Candida antarctica lipase A provided racemic cyanohydrin butanoates with quantitative chemical yields under mild conditions. [Copyright &y& Elsevier]

A series of novel (R)-furylbenzotiazol-based cyanohydrin acetates were prepared in over 90% isolated yields from the corresponding furancarbaldehydes. The one-pot method combines a basic resin to produce hydrogen cyanide from acetone cyanohydrin, an equilibrium between the formation and decomposition of furylbenzotiazol-based cyanohydrins and the unique enantioselectivity of Candida antarctica lipase A, allowing the acylation of (R)-cyanohydrins in the presence of vinyl acetate in anhydrous acetonitrile. [Copyright &y& Elsevier]

A novel route to chiral ferrocene derivatives involving the application of hydroxynitrile lyase from Hevea brasiliensis has been developed. The method allows the conversion of formylferrocene 1 and 1,1′-diformylferrocene 2 into their corresponding chiral cyanohydrins. (R)-(Cyanohydroxymethyl)ferrocene 3 and (R,R)-1,1′-bis(cyanohydroxymethyl)ferrocene 4 were obtained in high yield and stereochemical purity using this method. The full structural characterisation of the latter including the determination of diastereomeric purity and the assignment of the absolute configuration is disclosed. [Copyright &y& Elsevier]

Methods for the catalytic asymmetric synthesis of cyanohydrins derived from both aldehydes and ketones are reviewed. Successful catalysts based on enzymes, peptides and transitional metal complexes are included, and mechanistic detail is included where appropriate. Illustrations of the many synthetic applications of non-racemic cyanohydrins are given. [Copyright &y& Elsevier]

The asymmetric epoxidation of allylic cyanohydrins using the Sharpless kinetic resolution (SKR) reaction was explored. The SKR methodology was extended to enals via in-situ conversion into the corresponding cyanohydrin. The prospect of achieving a dynamic Sharpless kinetic resolution was investigated and the enantioselectivity of the SKR of (E)-2-hydroxy-3-methyl-4-phenyl-3-butenenitrile 1 studied. Reversible hydrocyanation of α-methyl cinnamaldehyde was developed and a one-pot hydrocyanation/epoxidation process achieved. [Copyright &y& Elsevier]

Guanabana seed meal is a source of (S)-oxynitrilase which biocatalyzes the enantioselective addition of HCN to aromatic, heteroaromatic and α,β-unsaturated aldehydes to produce cyanohydrins. [Copyright &y& Elsevier]