A Pool for Chiral Hydroxyalkanoic Acids

Chiral R-form hydroxyalkanoic acids are normally difficult to synthesize by chemical means. The occurrence of over 120 different chiral R-forms of PHA monomers reflects the low substrate specificity of PHA synthases, which are the key enzymes of PHA biosynthesis [7, 8, 22], These can be used as a rich pool of chrial compounds [13]. In addition, the importance of bacterial anabolism and catabolism, which provide the coenzyme A thioesters of the respective monomers as substrates to these PHA synthases, is also important in controlling the structure of hydroxyalkanoic acids [23]. 

R-3-hydroxybutyrate (3HB) was reported to be used for the synthesis of carbapenem antibiotics [6]. Other 3-hydroxy acids were also reported to be used as chiral building blocks for the synthesis of macrolides such as pyrenophorin, col-letodiol, grahamimycin A1 and elaiophylidene [6]. The transformation of 3-hydroxyaIkanoates (3HA) to their dioxanone enolates allows the subsequent synthesis of various 3HA derivatives. 3HB dioxanone enolates can be used as intermediates for synthesis of beta-lactones and 2-aIkylated 3HB [6]. 

3HB can also be used to synthesize dendrimers that possess the advantages of biodegradability, monodispersity and large numbers of surface functional moieties, which can be expected to be promising for in vivo drug delivery. Sodium 3HB 

---