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Monatin and Its Stereoisomers: Chemoenzymatic Synthesis and Taste Properties
Author(s) -
Bassoli Angela,
Borgonovo Gigliola,
Busnelli Gilberto,
Morini Gabriella,
Drew Michael G. B.
Publication year - 2005
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400589
Subject(s) - stereocenter , chemistry , absolute configuration , diastereomer , stereochemistry , aspergillus oryzae , isomerization , chirality (physics) , chiral column chromatography , enantiomer , enantioselective synthesis , organic chemistry , enzyme , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark , catalysis
Abstract The sweet natural compound monatin 1 has two stereogenic centres and the (2 S ,4 S ) absolute configuration has been attributed to the natural isomer. We obtained all four stereoisomers as pure compounds by a six‐step synthetic sequence. The stereogenic centre at C‐4 was introduced stereoselectively by a regio‐ and enantiospecific enzymatic hydrolysis of the racemic ethyl dicarboxylate 4 using a protease from Aspergillus oryzae . The absolute configuration of the intermediate products was assigned by X‐ray diffraction of chiral derivatives. The stereogenic centre at C‐2 was introduced non‐specifically, and the resulting diastereomeric mixtures were separated by RP‐HPLC. The absolute configurations of the final products were established by comparing retention times on a chiral HPLC column with those of known samples. The four stereoisomers were submitted to tasting trials and three of them, particularly the (2 R ,4 R ) isomer, were found to be intensely sweet. A sample of natural monatin analysed under the same conditions is shown to contain all the four stereoisomers. The relative stereoisomeric content in the plant, as well as the possible isomerisation of the chiral centres during extraction and manipulation of monatin samples, are important points that need to be clarified by extensive analysis of the natural extracts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)