Synthesis and Analysis of the Sterically Constrained L-Glutamine Analogues (3S,4R)-3,4-Dimethyl-l-glutamine and (3S,4R)-3,4-Dimethyl-l-Pyroglutamic Acid |
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Authors: | Acevedo Cristina M Kogut Eugene F Lipton Mark A |
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Institution: | Department of Chemistry, Purdue University, West Lafayette, IN 47907-1393. |
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Abstract: | The nonproteinogenic amino acids (3S,4R)-3,4-Dimethyl-l-pyroglutamic acid and (3S,4R)-3,4-dimethyl-l-glutamine -- found in the cyclic depsipeptides callipeltin B, callipeltin A, and papuamide A -- were synthesized from a common intermediate derived from l-pyroglutamic acid. The diastereoselective introduction of the methyl groups was accomplished by cuprate addition and enolate alkylation, followed by a kinetic epimerization of the C-4 methyl substituent. (3S,4R)-3,4-dimethyl-l-glutamine shows a conformational restriction of its side chain which may be related to its biological function in the natural products where it is found. |
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