4-hydroxybutyrate -hydroxycarboxylic acid

Optically active 3-amino-2-hydroxycarboxylic acid derivatives are often key components of medicinally important compounds. The synthesis of isopropyl (2i ,35)-3-amino-4-cyclo-hexyl-2-hydroxybutyrate (126) (Scheme 28) takes advantage of a [2 + 2]-cycloaddition reaction of the chiral imines 123, prepared from 63, to assemble the important diastereomeric azetidinone 124 as the crucial precursor for completion of this novel synthesis. Protection of the hydroxy group of 63 as either the TBS ether 119 or the tert-buty ether 120, followed by a DIBAL reduction at —78 °C, produces smoothly one of the aldehydes 121 or 122. Condensation of these aldehydes with either di-p-anisylmethylamine or benzylamine in the presence of anhydrous magnesium sulfate affords the four possible chiral imines 123a—d (Scheme 26). 

Other approaches to improve the properties of PHB is the production of derivatives based on PHB via the biosynthesis of copolyesters containing PHB units with other 3-hydroxyalkanoates units [19], such as poly [3-hydroxybutyrate-co-hydroxyvalerate] [PHBV] [20] or poly [3-hydroxybutyrate-co-3-hydroxyhexanoate] [21], with different molar ratios of hydroxycarboxylic acids. This approach has been investigated extensively [22] because it can... 

Racemic (3-hydroxycarboxylic acids can be synthesized by means of the Reformatsky reaction and the chemical reduction of P-keto acids. Lehninger et al. reported the optical resolution of racemic p-hydroxybutyric acid with quinine as a resolving agent [6] (Scheme... 

The authors proceeded to evaluate the production of (i )-P-hydroxycarboxylic acids from carboxylic acids by strain NBA-2. The results, shown in Table 5, were that, in addition to (/ )-P-hydroxybutyric acid, (/ )-(3-hydroxyvaleric acid, (/ )-3-hydroxycaproic... 

Using the purified (S)-3-hydroxycarboxylate oxidoreductase (107) and two forms of NADPH regeneration led to the chiral 3-hydroxy carboxylates shown in Table 28 (83). All products of the bioreduction procedures showed ee values greater than 98 %. On the basis of the optical rotation value reported (108) the synthesized 3-hydroxybutyrate was the (5)-enantiomer. It was assmned that the configuration of the other prepared 3-hydroxycarboxylates was the same. As checked with racemic mixtures of the derivatives of the four 3-hydroxy acids mentioned in Table 28, the applied chiral gas/liquid chromatography columns separated the enantiomers. For details see (83). 

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