Synthesis of novel beta-lactone inhibitors of fatty acid synthase

Abstract

Fatty acid synthase (FAS) is necessary for growth and survival of tumor cells and is a promising drug target for oncology. Here, we report on the syntheses and activity of novel inhibitors of the thioesterase domain of FAS. Using the structure of orlistat as a starting point, which contains a beta-lactone as the central pharmacophore, 28 novel congeners were synthesized and examined. Structural features such as the length of the alpha- and beta-alkyl chains, their chemical composition, and amino ester substitutions were altered and the resulting compounds explored for inhibitory activity toward the thioesterase domain of FAS. Nineteen congeners show improved potency for FAS in biochemical assays relative to orlistat. Three of that subset, including the natural product valilactone, also display an increased potency in inducing tumor cell death and improved solubility compared to orlistat. These findings support the idea that an orlistat congener can be optimized for use in a preclinical drug design and for clinical drug development.

Figure 1

Molecular structure of tetrahydrolipstatin (orlistat) and the structural features modified in this study. Modifications were made to reduce the overall hydrophobicity of the compounds and then tested for retention of activity. Several compounds with variation at one or a combination of these features were shown to have increased potency toward FASTE in a fluorogenic biochemical assay.

Figure 2

Differential cytotoxicity in MDA-MB-231 and Hs58.Fs cells are a model platform for screening FASTE inhibitors, as shown by the pharmacological and siRNA inhibition of FAS. MDA-MB-231 tumor cells and primary cultures of Hs58.5s fibroblasts were exposed to 100 nM FAS siRNA or nonsilencing control siRNA and 25 μM orlistat or vehicle control for 72 h. Cellular cytotoxicity was monitored by measuring DNA fragmentation. Values are means ± SE of four samples per treatment group.

Scheme 1

Syntheses of the Thiopryridyl Ketene Acetals

Scheme 2

Synthesis of the Chiral Aldehyde 8a from Malic Acid Involving Cuprate Addition

Scheme 3

Syntheses of Chiral Aldehydes 8b–g via Noyori Reduction

Scheme 4

Tandem Mukaiyama Aldol-Lactonization Process and Deprotection Delivering β-Lactones 13/14

Scheme 5

Introduction of the α-Amino Ester Moiety via Mitsunobu Reaction (with Inversion) or Acylation (with Retention) at C6, Providing Orlistat Derivatives 15–17

Scheme 6

Alternative Strategy for Modification of the δ-Side Chain Involving Olefin Cross-Metathesis and Hydrogenation