220047-75-6Relevant academic research and scientific papers
Reciprocity of steric and stereoelectronic effects in the collagen triple helix
Shoulders, Matthew D.,Hodges, Jonathan A.,Raines, Ronald T.
, p. 8112 - 8113 (2007/10/03)
In previous work, we demonstrated that 4-fluoroproline residues can contribute greatly to the conformational stability of the collagen triple helix, and that this stability arises from stereoelectronic effects that fix the pucker of the pyrrolidine ring and thereby preorganize the backbone properly for triple-helix formation. Here, we take a reciprocal approach, demonstrating that the steric effect of a 4-methyl group confers stability similar to that from a 4-fluoro group in the opposite configuration. Such fundamental interplay between steric and stereoelectronic effects is heretofore unknown in proteinsnatural or syntheticand provides a new means to modulate conformational stability. Copyright
Asymmetric hydrogenations for the synthesis of boc-protected 4-alkylprolinols and prolines
Del Valle, Juan R.,Goodman, Murray
, p. 3923 - 3931 (2007/10/03)
The utility of 4-substituted prolinols and their corresponding prolines in peptides, peptidomimetics, and natural products has motivated researchers to find new and efficient routes for their preparation. Herein, we report a general approach to the synthesis of Boc-protected 4-alkylprolinols and prolines via a divergent asymmetric hydrogenation strategy. Intermediate exocyclic olefins were prepared by Wittig-type reactions with ketone 6 and subjected to hydroxyl and sterically directed reductions. The Crabtree catalyst (Ir[COD] PyPCy3PF6) proved to be highly effective in diastereoselective hydrogenations to give trans- substituted pyrrolidines (9). Good facial selectivities were also observed in heterogeneous hydrogenations with Raney-nickel to obtain cis-substituted pyrrolidines (11). Employing this strategy, we describe the synthesis of novel prolinol and proline-based building blocks for incorporation into biologically relevant peptidomimetics.
