Biomedical subjects

Alan Whitehead

Publications and source records attributed to Alan Whitehead.

3 recordsLinked to original sources

PubMed2006

Divalent activation in temporary phosphate tethers: highly selective cuprate displacement reactions.

Desymmetrization of a readily derived pseudo-C(2)-symmetric monocyclic phosphate via highly diastereoselective anti-S(N)2' allylic displacement reactions is reported. This method utilizes of a wide variety of zinc-derived organocuprates to afford E-1,2-syn-configured phosphate acid building blocks. Extension of this protocol to unsymmetric monocyclic phosphates exclusively yields 1,2-anti-configured products. Within this study, stereoelectronic factors, coupled with allylic strain, ultimately govern regio- and diastereoselective cuprate reactions, further substantiating the Corey mechanism for organocuprate additions into allylic esters. [reaction: see text]

Alcohols↗

PubMed2005

P-heterocyclic building blocks: application to the stereoselective synthesis of P-sugars.

A strategy relying on the utilization of stereoselective additions to allyldiphenylphosphonate esters and subsequent ring-closing metathesis (RCM) to access P-chiral P-heterocyclic building blocks for the synthesis of phosphono sugars is described. These building blocks possess several attractive components, including the following: (i) P(2) and C(6) stereogenic centers for directing stereoselective transformations; (ii) an activated C(3) methylene group that promotes base-mediated olefin transposition to generate vinyl phosphonates available for further stereoselective reactions; and (iii) a P(2)-stereogenic center containing an exchangeable phosphonate ester armed to attenuate the "stereochemical environment" at phosphorus. Taken collectively, these attributes contribute to a concise method for the stereoselective synthesis of an array of P-sugars.

Carbohydrates↗

PubMed2005

Multivalent activation in temporary phosphate tethers: a new tether for small molecule synthesis.

[reaction: see text]. A new tether for small molecule synthesis is reported. This functionally active tether mediates the desymmetrization of a pseudo-C(2)-symmetric tris-allylic phosphate triester to generate a P-chiral bicyclo[4.3.1]phosphate containing ample steric and stereoelectronic differentiation for investigating chemo-, regio-, and stereoselective transformations. Overall, the method reported herein demonstrates a fundamentally new role of phosphates in synthesis and provides differentiated polyol building blocks for use in natural product synthesis.

Biological Products↗