Proline methyl ester hydrochloride, acidity

Figure 25 Fluorescence response upon addition of various analytes into a solution of 49 (0.1 mM) and 52 (1.0 mM). Acetylcholine (o), glycine ( ), L-aspartic acid (A), L-proline ( ), L-phenylalanine ethyl ester hydrochloride ( ), and glycine methyl ester hydrochloride (<>). (Adapted from Ref. 58. American Chemical Society, 1996.)...

In recent years, silicon-containing derivatives of proline have attracted considerable attention of chemists. The replacing proline by these unnatural amino acids, which are more stable towards proteolytic degradation, may increase the bioavailability of the structurally similar peptides without a modification of their conformational and biological properties (104). Currently, the Schdllkopf method is the only proven approach for the synthesis of silaproline cycle (105). Hydropyrazine is hydrolyzed under mild conditions to yield hydrochloride of 3-[(iodomethyl) (dimethyl) silyl] alanine methyl ester. The reaction of the latter with amine affords a product of the intramolecular cyclization of the 4,4-dimethyl-4-sila-proline methyl ester and its interaction with (t-Boc)20 gives rise to the corresponding N-t-Boc-silaproline methyl ester 133 (Scheme 24.17). 

Radley and co-workers [133] reported that when chiral dopants—decyl esters of amino acids, serine, alanine, leucine, and methionine—were added to an aqueous solution of alkyl methyl ammonium bromides, mixed with decanol, amphiphilic cholesteric crystals were formed. They found that the sense and magnitude of the induced helix by decyl ester of amino acid hydrochlorides except decyl ester of alanine are dependent on the achiral cationic surfactant, alkyl methyl ammonium bromides. The formation of amphiphilic cholesteric crystals was interpreted in terms of the trans and cis ro-tamers of the chiral ester of amino acid, associated with the ester linkage. Also, they reported [134] that in the case of the ester hydrochloride of proline as a chiral dopant, a concentration-dependent reversal in helical twist was observed. 

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