6-t-Butoxy-3,5-dihydroxyhexanoic esters in which the steric configurations at the 3- and 5-positions are (R)-configuration and (S)-configuration, respectively, are known to be easily converted to a lactone moiety of the chemical structures of compactin and mevinolin which are attracting attention as cholesterol reducing agents [cf. K. Prasad et al., Tetrahedron Lett., Vol. 25, p. 3391 (1984)]. The lactone moiety stated above is assumed to be an active part of an inhibitor on 3-hydroxy-3-methylglutaryl-CoA reductase, one of the predominant enzymes regulating cholesterol biosynthesis, and a number of analogues having this lactone moiety have been synthesized [cf. J. R. Prous (ed.), Drugs of the Future, Vol. 12, No. 5, p. 437 (1987)].
Conventional processes applicable to synthesis of optically active 6-t-butoxy-3,5-dihydroxyhexanoic esters include a process for synthesizing an optically active 1,3-diol compound by making use of naturally occurring D-glucose as reported in T. Lee et al., Tetrahedron Lett., Vol. 26, p. 4995 (1985) and Y. Yang et al., Tetrahedron Lett., Vol. 23, p. 4305 (1982). Further, methods for constructing the two asymmetric carbon atoms one by one include a method comprising diastereo-selective reduction by using a trialkylboron as a specific reactant as described in K. Chen et al., Tetrahedron Lett., Vol. 28, p. 155 (1987), a method comprising asymmetric aldol reaction as described in J. E. Lynch et al., Tetrahedron Lett., Vol. 28, p. 138 (1987), a method of using asymmetric epoxidation as described in K. Prasad et al., Tetrahedron Lett., Vol. 25, p. 3391 (1984), and a method of using a microorganism as described in P. R. Ortizo De Montellano et al., J. Am. Chem. Soc., Vol. 98, p. 2018 (1976).
The process for obtaining an optically active 1,3-diol compound by using a naturally occurring substance is disadvantageous in that long reaction steps are required for obtaining the desired product. The processes starting with an optically active substance obtained by optical resolution are inevitably attended by production of an unnecessary enantiomer, giving rise to a problem of production efficiency. Further, in the processes using a microorganism, the steric configuration of the product is limited in many cases and, also, separation of the product from microbial cells is complicated.
A diastereoselective technique in which one asymmetric point is made use of to induce another asymmetry may be applied to synthesis of the 1,3-diol compound according to the present invention. However, such configurational control generally requires an expensive reagent.