Mandeuc acid

From Precursors Derived from Lactic and MandeUc Acids... 

Deracemization of mandelic add with the combined action of two enzymes has been reported. rac-MandeUc acid is acylated by a Pseudomonas sp. lipase in diisopropyl ether. After solvent removal the mfacture of mandeUc acid enriched in the R-form and the 0-acetyl derivative of the S-configuration are subjected to the mandelate racemase-catalyzed racemization in aqueous buffer. In these conditions only the non-acetylated hydroxy acid is racemized. In order to obtain (S)-0-acetylmandelic acid in an 80% isolated yield and a >98% e.e. the process must be repeated four times [9]. 

Alternatively, a one-pot, single-step deracemization of sec-alcohols has been achieved by employing two different microorganisms in a single reaction vessel. However, the number of examples of this type is limited and the oxidation and reduction steps are usually performed sequentially in a one-pot, two-step procedure. For instance, racemic mandeUc acid was deracemized in the presence of whole cells of Pseudomonas polycdor and Micrococcus freudenreichii [14]. Separate experiments showed that P. polycolor was responsible for the oxidation, while M. freudenreichii was needed for reduction of the corresponding a-keto acid. After 24h, (R)-mandelic acid 4 was isolated in a 60% yield and 99% e.e. [14],... 

Pummerer rearrangement (5,3-4). The Pummerer rearrangement of jS-liydroxy sulfoxides to derivatives of a-hydroxy aldehydes has been extended to the rearrangement of 3-keto sulfoxides. Thus rearrangement of (1) with acetic anhydride-sodium acetate in toluene under reflux gives the S-aryl thioester (2) in 74% yield. The ester is hydrolyzed by base to mandeUc acid (3). In the altscnce of sodium acetate the normal product of the Pummerer rearrangement... 

Fig. 3.12 Chiral resolution of mandeUc acids by ligand-exchange LC.

The mandelic acid was separated from the ammonium chloride by extraction with hot benzene. This was best done by dividing the solid mixture into 10 approximately equal parts. One of these portions was placed in a flask with 1 L boiling benzene. After a few minutes, the hot benzene solution was decanted through a suction funnel. The filtrate was cooled in an ice bath, and the mandelic acid that crystallized was filtered with suction. The benzene was returned to the extraction flask containing the residue from the first extraction, and a new portion of the ammonium chloride-mandeUc acid mixture was added and extracted as before. The process was repeated until the mandeUc acid was completely removed Ifom the ammonium chloride. The amount of pure white mandelic acid, melting at 118°C, was 229-235 g, with a corresponding 50-52% yield. 

Melasma was also shown to improve up to 50% after a month of using mandeUc acid 10% lotion. Lactobionic acid belongs to a newer polyhydroxy acid group that effects a decrease in pigmentation in a similar manner but with lesser irritant effect. 

The application of proUne methylester as an auxihary in the stereoselective reduction of a-keto amides is such an example [29]. This process is interesting because of the opportunity to obtain mandeUc acid derivatives in both optically pure forms from one single proUne enantiomer. 

Pischel U, Abad S, Miranda MA (2003) Stereoselective fluorescence quenching by photoin-duced electron transfer in naphthalene-amine dyads. Chem Commun 1088-1089 Xu M H, Lin J, Hu Q et al (2002) Fluorescent sensors for the enantioselective recognition of mandeUc acid signal amplification by dendritic branching. J Am Chem Soc 124 14239-14246... 

Endo T, Tamura K, inventors Nitto Chemical Industry Co., Ltd., assignee. Process for producing R(—)-mandeUc acid and derivatives thereof. EP 0449648.1991 Oct 02. 

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