Cyclic peptide—cyanohydrin complex

The non-equivalence of enantiomers through the spontaneous breaking of mirror-symmetry in nature is amplified by asymmetric autocatalytic reaction [34], e.g. Frank s spontaneous asymmetric synthesis [35, 36] (Fig. 7-8). Alberts and Wyn-berg have reported in enantioselective autoinduction that chiral lithium alkoxide products may be involved in the reaction to increase the enantioselectivity (Eq. (7.9)) [37]. The product % ee however does not exceed the level of catalyst % ee. In asymmetric hydrocyanation catalyzed by cyclic dipeptides, the (Si-cyanohydrin product complexes with the cyclic peptide to increase the enantioselectivity in the (S)-cyanohydrin product, the reaction going up to 95.8% ee (Eq. (7.10)) [38]. In the presence of achiral amine, (/ )-l-phenylpropan-l-ol catalyzed carbonyl-addition reaction of diethylzinc has been reported to show lower % ee than that of the catalyst employed [39]. 

Keywords a-Cyanoliydrin, a-Aminonitrile, Hydrogen cyanide. Acetone cyanohydrin, TMSCN, Lewis acid. Cyclic dipeptide. Peptide-metal complex, Strecker synthesis... 

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-... 

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