Dl-Mandelic acid

Frankland and Price 17 were the first to attempt the resolution of alcohols (and acids) by fractional crystallization of their solid esters. The isomeric solid esters formed from Z-s-butylcarbinol and di-dibenzoyl-glyceric acid failed to separate on crystallization the corresponding di-alcohol-i-acid ester was liquid. Marckwald and McKenzie 18-19 effected partial resolutions of dl-mandelic acid and related acids with 1-menthol and d-bomeol, and of di-2-octanol with d-tartaric acid, but did not develop a satisfactory method for resolving alcohols. Later investigators, however, have employed the following resolving agents in several more or less successful resolutions of certain alcohols (a) i-menthyl isocyanate, (6) d-camphoric acid, (c) d- or i-mandelic acid, (d) d- or... 

The principles outhned above were ap ed by Marckwald and McKen-Qe for the partial resolution of a rao nio acid with an active alcohrfl. Thus when dl-mandelic acid was heated with less than one equivalent (ff Lmenthol, the resulting ester contained somewhat more 1-menthyl-d-mandelate than I-menthyl-l-mandelate and the unesterified acid contained a correqxmding excess of 1-mandelic acid. Also, when a mixture of equal amounts of the two diastereoisomeiic esters was partially hydrolyzed, the regenerated acid and that still combined in the residual ester contained unequal amounts of the two antipodes. The process has been extended to the resolution of acids and amines through the formation and hydrolysis of amides. ... 

In a modified procedure, an optically inactive adsorbent (such as alumina) has been coated with a thin layer of an optically active substance. Resolution of dl-mandelic acid is an example of separation belonging to this category. 

Mandelic Acid Isoamyl Ester, a-Hydroxybenzene-acetic acid 3-methylbutyl ester mandelic acid isopentyl ester isoamyl mandelate Atractyl Spasmol Mandaverm Vermi-parin Spasmostenyl. C,jH,Oj mol wt 222.27. C 70.24%, H 8.16%, O 21.59%. Prepd by esterification of dl-mandelic acid with an excess of isoamyl alcohol in the presence of coned H]SO( Rona et al, Biochem. Z. 181, 50 (1927). Improved procedure Brock et al, Arzneimittel-Forsch. 2, 166 (1952). 

Synonyms Amygdalic acid Amygdalinic acid Benzoglycolic acid Glycolic acid, phenyl- a-Hydroxyphenylacetic acid o-Hydroxy-a-toluic acid DL-Mandelic acid L-Mandelic acid Paramandelic acid Phenylglycolic acid... 

DL-Mandelic acid L-Mandelic acid. See Mandelic acid... 

Zirconia + hafnia in zircon and zirconia. Gravimetrically by DL-mandelic acid. 

With this resin DL-mandelic acid (hydroxyphenylacetic acid) (1) could be partially resolved if dioxane or mixtures consisting of chloroform and methanol were used as eluant. Quantitative investigations showed that the mandelic acid was recovered completely and that the antipodes were partially enriched in subsequent fractions of the eluate in equi-... 

Fig. 1. Chromatography of 190 mg DL-mandelic acid on polymer 1 (column dimensions 600X10 mm eluant dioxane 1.5 cm volumina of fractions 1.1 cm total concentration optical purity a measured rotation angle a ).

The adsorbents with a —(SO2 —NH—)— or —(CH2 —NH—)— linkage between the polystyrene matrix and the optically active amine compound had only a very low resolution efficiency for DL-mandelic acid. The maximal enrichment was 0.2—0.8%, the optical total enrichment was below 0.1%. This failure might be caused by a too weak chromatographic efficiency of the chiral centres. 

If the methyl group of polymer 3 was replaced by a carbonyl group as in polymer 6 (6 obtained by reacting polystyrenesulfochloride with D-a-aminophenylacetic acid) the resolution efficiency for DL-mandelic acid was improved distinctly (see Table II). 

The chromatographic efficiency of these polymers was studied with DL-mandelic acid (I) resp. with DL-2-phenyl glycine (20). As it can be seen in Table II the resolution efficiency of the adsorbants (AOP) in the COOH-form showed the following order 6 (phenyl) <... 

As racemic mixtures DL-mandelic acid (I), DL-2-phenyl glycine hydrochloride (VII), and DL-phenylethylamine hydrochloride (X) were chosen. Water was used as eluant. With both adsorbants only the unchanged racemic mixtures were recovered. But as expected after saponification of polymer 9 to 11, DL-mandelic acid (I) and DL-2-phenyl glycine (VII) could be partially resolved. Polymer 11 is similar to 7, but it contained practically no SOaH-groups. 

While in polymers 9 and 10 the esterification of the carbonyl groups leads to a loss of the resolution, this did not occur if the racemic mixtures were esterified. DL-mandelic acid methyl ester (II) could be partially resolved using polymer 11 and methanol as eluant. Compared to the chromatography of DL-mandelic acid (I) with water the elution was distinctly faster, the elution curves were more symmetrical but the sequence of the antipodes was reversed. 

Also during the elution of DL-mandelic acid (I) with methanol from polymer 11 first positively and then negatively rotating fractions were obtained (see Table II). The chromatograms of (I) and (II) were similar, as the mandelic acid was esterified during the elution with methanol. 

C6H5, —OH, or —H at the chiral centre of the mandelic acid for a methyl group we repeated our tests with DL-a-phenylethanol (III), and DL-2-phenylpropionic acid (VI) (eluant methanol) and with a-methyl-DL-mandelic acid (IV) and DL-lactic acid (V) (eluant methanol or water). Only in the case of a-methylmandelic acid (IV) (eluant methanol) was a weak resolution noticed (maximal 0.5%, optical total enrichment 0.1%). 

In most cases polysalt formation can be excluded in examining the reason for the obtained resolutions, as most polymers can only bind basic racemic mixtures as salts. A reasonable explanation for the partial resolution of DL-mandelic acid (I) might be the formation of diastereomeric adsorbates. Also it seems that the resolution of DL-a-aminophenylacetic acid (VII) does not proceed via salt formation mainly. 

The purified enzyme displays its highest activity at 50°C. Furthermore, the enzyme is fairly stable because more than 90% of the activity is retained after a preincubation for 30 min up to 55°C. The L-aminoamidase is active between pH values of 6.5-11.0, with a broad pH optimum at pH values of 8.0-9.5 (Fig. 9). Determination of the substrate specificity of the purified enzyme showed that this amide hydrolase was active toward a rather broad range of bodi a-H- and a-alkyl-substituted amino acid amides (Table 8). Within these two substrate classes, highest activity is observed for file cyclic amino acid amide DL-proline amide and the a-alkyl-substituted amino acid amides DL-isovaline amide and DL-a-allylalanine amide. Furthermore, this enzyme displays modest activity toward a number of simple amides (e.g., acetamide and propionamide). The enzyme appears to be inactive with the a-hydroxy acid amide DL-mandelic acid amide and with the dipeptide L-Phe-L-Leu. These results clearly show that this purified amide hydrolase belongs to the group of aminoamidases. 

By this procedure three microorganisms could be identified that hydrolyzed DL-mandelic acid amide completely L-enantiospecific. The most interesting one of these three strains, based on its high cellular activity, could be identified as an Ochrobactrum anthropi strain, and this strain has been deposited at the NCIMB culture collection as NCIMB 40321. 

---