The synthesis of (11R,12S)-lactobacillic acid and its enantiomer

(11R,12S)-Lactobacillic acid has been prepared from 2,3-O-isopropylidene-d-glyceraldehyde, in a sequence involving asymmetric cyclopropanation, and from cis-cyclopropane-1,2-dimethanol, using enzymatic desymmetrisation. The key step in the former route was the stereochemically controlled cyclopropanation of (1Z,4′S)-(2′,2′-dimethyl-1′,3′-dioxolan-4′-yl)-1-octene via a Simmons–Smith type reaction, using diethylzinc and chloroiodomethane. This product was converted into the key intermediate (1R,2S)-1-formyl-2-hexylcyclopropane, which was also obtained by a known sequence from the (1R,2S)-monobutyrate ester of cis-cyclopropane-1,2-dimethanol. This pivotal aldehyde was converted into (11R,12S)-lactobacillic acid. Using analogous chemistry, the (11S,12R)-enantiomer of lactobacillic acid was prepared from 2,3-O-isopropylidene-d-glyceraldehyde or from the (1S,R)-monobutyrate ester of cis-cyclopropane-1,2-dimethanol.