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Inversion of Stereoselectivity by Applying Mutants of the Hydroxynitrile Lyase from Manihot esculenta
Author(s) -
Bühler Holger,
Miehlich Burkhard,
Effenberger Franz
Publication year - 2005
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.200400302
Subject(s) - stereoselectivity , chemistry , cyanohydrin , stereocenter , enantiomer , stereochemistry , mutant , aldehyde , racemization , catalysis , organic chemistry , enantioselective synthesis , biochemistry , gene
The influence of Trp128‐substituted mutants of the hydroxynitrile lyase from Manihot esculenta (MeHNL) on the stereoselectivity of MeHNL‐catalyzed HCN additions to aldehydes with stereogenic centers, which yield the corresponding cyanohydrins, is described. In rac ‐2‐phenylpropionaldehyde ( rac ‐ 1 ) reactions, wild‐type (wtMeHNL) and all MeHNL Trp128 mutants are highly ( S )‐selective toward the ( R ) enantiomer of rac ‐ 1 ; this results exclusively in (2 S ,3 R )‐cyanohydrin ((2 S ,3 R )‐ 2 ) with ≥96 % de . The ( S ) enantiomer of rac ‐ 1 , however, only reacts ( S )‐selectively with wtMeHNL to give (2 S ,3 S )‐ 2 with 80 % de , whereas with Trp128 mutants, ( R ) selectivity increases with decreasing size of the amino acids exchanged. The MeHNL W128A mutant is exclusively ( R )‐selective, resulting in (2 R ,3 S )‐ 2 with 86 % de . The reaction behavior of rac ‐phenylbutyraldehyde ( rac ‐ 5 ) is comparable with rac ‐ 1 , which also inverts the stereoselectivity from ( S ) to ( R ) when the enzyme is exchanged from wtMeHNL to the W128A mutant. Stereogenic centers not adjacent to the aldehyde group, as in 7 and 9 , do not influence the stereoselectivity of MeHNL catalysis, and ( S ) selectivity is observed in all cases. Stereoselectivity and inversion of stereoselectivity of MeHNL Trp128 mutant‐catalyzed cyanohydrin formation can be explained and rationalized with crystal‐structure‐based molecular modeling.