Asymmetric Synthesis of N-Substituted alpha-Aminobenzlactam via Crystallization-Induced Asymmetric Transformation of Covalent Diastereomer

A Facile Strategy for the High Yielding, Quantitative Conversion of Polyglycol End-Groups to Amines

Amino end-group functionalised polyglycols are important intermediates in the synthesis of sophisticated polymeric architectures and biomaterials. Herein, we report a facile strategy for the end-group conversion of hydroxyl-terminated polyglycols to amino-terminated polyglycols in high isolated yields and with excellent end-group fidelity. Following traditional conversion of polyglycol hydroxyl end-groups to azides via the corresponding mesylate, reduction with zinc in the presence of ammonium chloride afforded a range of amino end-group functionalised poly(ethylene glycol) and poly(propylene glycol) homopolymers and copolymers with isolated yields of 82-99% and end-group conversions of >99% as determined by NMR spectroscopy and MALDI ToF MS. Furthermore, this process is applicable to a sequential reagent addition approach without intermediate polymer isolation steps with only a slight reduction in yield and end-group conversion (95%). Importantly, a simple work-up procedure provides access to high purity polyglycols without contamination from other reagents.

A Novel Crystallization-Induced Diastereomeric Transformation Based on a Reversible Carbon−Sulfur Bond Formation. Application to the Synthesis of a γ-Secretase Inhibitor

This paper describes a remarkably efficient process for the preparation of gamma-secretase inhibitor 1. The target is synthesized in only five steps with an overall yield of 58%. The key operation is a highly selective and practical, crystallization-driven transformation for the conversion of a mixture of tertiary benzylic alcohols into the desired sulfide diastereomer with 94:6 dr. This unprecedented process is based upon a reversible carbon-sulfur bond formation under acidic conditions.

Efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921

[reaction: see text] An efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921 was accomplished. Two short enantioselective syntheses of the common key intermediate (S)-alpha-aminoazepinone 6b were developed. Olefin 3 was converted to 6b via asymmetric hydrogenation. Alternatively, enyne 12 was converted to racemic alpha-aminoazepinone 15b, which was transformed to 6b by a practical dynamic resolution.

Practical enantioselective synthesis of endothelin antagonist S-1255 by dynamic resolution of 4-methoxychromene-3-carboxylic acid intermediate

A practical multikilogram-scale synthesis of enantiomerically pure S-1255 (1), a potent and orally active ET(A) receptor antagonist, is described. Utilizing readily available starting materials and reagents, the entire sequence of reactions starting from 2,5-dihydroxyacetophenone 8 proceeded under mild conditions to give 1 in an excellent chemical yield (8 steps, 41% overall yield) and in a high enantiopurity (98% ee). The crucial step of the synthesis is a dynamic resolution of key intermediate 16. (R)-Methoxy acid (R)-16 having 97-99% ee was obtained in 83-84% yield from racemic 16 as a crystalline (1S,2R)-(+)-norephedrine or (+)-cinchonine salt by the dynamic resolution comprising concurrent crystallization and in situ racemization. A mechanism of the dynamic resolution through a ring-opened zwitterionic intermediate is discussed. In the final synthetic step, an effective carbon-carbon bond formation between the C4 carbon and the p-anisyl group was accomplished by a conjugate addition-elimination reaction of Grignard reagent 3 to (R)-16 to give 1 having 98% ee. Owing to high efficiencies of functional group transformations, carbon-carbon bond formations, and the dynamic resolution, the synthesis required no chromatographic purification and was amenable to a multikilogram-scale preparation. Several kilograms of 1 for clinical trials were successfully prepared by this process.