Application of biocatalysis towards asymmetric reduction and hydrolytic desymmetrisation in the synthesis of a [small beta]-3 receptor agonist

Chemoenzymatic syntheses of two key intermediates in the preparation of a potent [small beta]-3 receptor agonist 1 are described. A lipase-catalysed hydrolytic desymmetrisation is employed in a new synthesis of intermediate 7, which avoids the use of alkyl-tin reagents. A second biotransformation delivers chiral chlorohydrin 5 from its parent ketone in greater enantiomeric excess than the previously-described Noyori-reduction process. A brief discussion of the enantioselectivity of a set of single-point mutants of Sporobolomyces salmonicolor aldehyde reductase in this bioreduction is also presented.