Practical asymmetric synthesis of a potent PDE4 inhibitor via stereoselective enolate alkylation of a chiral aryl-heteroaryl secondary tosylate

J Org Chem. 2005 Apr 15;70(8):3021-30. doi: 10.1021/jo048156v.

Abstract

A practical, chromatography-free catalytic asymmetric synthesis of a potent and selective PDE4 inhibitor (L-869,298, 1) is described. Catalytic asymmetric hydrogenation of thiazole ketone 5a afforded the corresponding alcohol 3b in excellent enantioselectivity (up to 99.4% ee). Activation of alcohol 3b via formation of the corresponding p-toluenesulfonate followed by an unprecedented displacement with the lithium enolate of ethyl 3-pyridylacetate N-oxide 4a generated the required chiral trisubstituted methane. The displacement reaction proceeded with inversion of configuration and without loss of optical purity. Conversion of esters 2b to 1 was accomplished via a one-pot deprotection, saponification, and decarboxylation sequence in excellent overall yield.

MeSH terms

  • 3',5'-Cyclic-AMP Phosphodiesterases / antagonists & inhibitors*
  • Combinatorial Chemistry Techniques*
  • Cyclic N-Oxides / chemical synthesis*
  • Cyclic N-Oxides / pharmacology
  • Cyclic Nucleotide Phosphodiesterases, Type 4
  • Enzyme Inhibitors / chemical synthesis*
  • Enzyme Inhibitors / pharmacology
  • Magnetic Resonance Spectroscopy
  • Molecular Structure
  • Pyridines / chemical synthesis*
  • Pyridines / pharmacology
  • Stereoisomerism

Substances

  • Cyclic N-Oxides
  • Enzyme Inhibitors
  • L 869298
  • Pyridines
  • 3',5'-Cyclic-AMP Phosphodiesterases
  • Cyclic Nucleotide Phosphodiesterases, Type 4