D-Oxynitrilase

Since the reaction has been reviewed recently (12) only a few additional facts will be mentioned. Many optically active cyanohydrins can be prepared (33) with e.e. s of 84 to 100% by the use of the flavopnotein D-oxynitrilase adsorbed on special (34) cellulose ion-exchange resins. Although the enzyme is stable, permitting the use of a continuously operating column, naturally only one enantiomer, usually the R isomer, is produced in excess. This (reversible) enzyme-catalyzed reaction is very rapid (34). Nonenzymic catalysts, such as the cinchona alkaloids, permit either enantiomer to be prepared in excess. 

Optically active cyanohydrins are obtained in good selectivity by the nucleophilic attack of cyanating reagents to chiral acetals.(21) However, the chiral auxiliaries are destroyed, and not recovered. In catalytic processes with chiral boryl compounds,(22) D-oxynitrilase,(23) and synthetic peptides,(24) the optical purities of the resulting cyanohydrins are generally not sufficient. 

Aschhoff, H.J. and Pfeil, U. (1970) Auftrennung and Charakterisiemng der Isoenzyme von D-Hydroxynitril-Lyase (D-Oxynitrilase) aus Mandeln. Hoppe-Seyler s Z. Physiol. Chem., 351, 818-26. 

In catalytic processes with enzymes such as D-oxynitrilase and (R) xynitrilase (mandelonitrilase) or synthetic peptides such as cyclo[(5)-phenylalanyl-(5)-histidyl], or in reaction with TMS-CN pro-mot by chiral titanium(IV) reagents or with lanthanide trichlorides, hydrogen cyanide adds to numerous aldehydes to form optically active cyanohydrins. The optically active Lewis acids (8) can also be used as a catalyst. Cyanation of chiral cyclic acetals with TMS-CN in the presence of titanium(IV) chloride gives cyanohydrin ethers, which on hydrolysis lead to optically active cyanohydrins. An optically active cyanohyrMn can also be prepared from racemic RR C(OH)CN by complexation with bru-... 

The application of (d)-oxynitrilase has been reported only recendy (159). The enzyme isolated from shoots of Sorghum catalyzes the condensation between various 3- and 4-suhstituted benzaldehydes and hydrogen cyanide resulting in (d)-cyanohydrins in 80-90% yield and up to 99% ee. 

D. V. Johnson, A. A. Zabelinskaja-Mackova, H. Griengl, Oxynitrilases for asymmetric C-C bond formation. 

Henry D. Dakin London, UK 1st enantioselective synthesis, with oxynitrilase... 

Johnson, D., Zahelinskaja-Mackova, A., and Griengl, H. 2000. Oxynitrilases for asymmetric C — C bond formation. Current Opinion in Chemical Biology, 4 103-9. 

Schliiter A-D (1998) Dendrimers with Polymeric Core Towards Nanocylinders. 197 165-191 Schmidt M, Griengl H (1999) Oxynitrilases From Cyanogenesis to Asymmetric Synthesis. 

Lyases None Lipoxygenase Amino acid decarboxylase Acetolactate decarboxylase D-amino acid oxidase Aldolases Oxynitrilases L-aspartase... 

The enantiomerically pure amino acids also can be produced through a similar synthetic pathway catalyzed by enzymes. For example, reaction of hydrogen cyanide with benzaldehyde catalyzed by either (R)- or (S)-oxynitrilase enzyme yields the enantiomeric cyanohydrins (R)- or (S)-mandelonitrile. Alternatively, by adding carbon dioxide and hydrogen cyanide and ammonia as feedstocks, aldehydes can be converted to hydantoins (4-alkylimidazolidine-2,5-diones), which can be then hydrolyzed with either D- or L- hydan-toinases to produce D- or L-a-amino acids, respectively. 

Oxynitrilase-Catalyzed Addition of HCN to Fluorinated Benzaldehydes. There have been similar advances in technology associated with the oxynitrilase-catalyzed addition of HCN to aromatic and aliphatic aldehydes and ketones 21,22). However, consistent with the documented low reactivity of the aldehydic carbonyl group of lOb-d all attempts to achieve oxynitrilase-catalyzed cyanohydrin formation failed (unpublished results). 

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