68739-90-2Relevant articles and documents
Preparation of enantiopure methionine, arginine, tryptophan, and proline benzyl esters in green ethers by Fischer–Speier reaction
Bolchi, Cristiano,Bavo, Francesco,Regazzoni, Luca,Pallavicini, Marco
, p. 1261 - 1268 (2018/06/11)
The simplest way to prepare the tosylate salts of amino acid benzyl esters, whose enantiomers are very important synthetic intermediates, is treatment of amino acid with benzyl alcohol and p-toluenesulfonic acid in a refluxing water-azeotroping solvent (Fischer–Speier esterification). However, to this day, the literature proposes only hazardous solvents, such as benzene, carbon tetrachloride, and chloroform, which must be absolutely avoided, or solvents, such as toluene and benzyl alcohol, which cause racemization because of too high boiling water azeotropes. On the other hand, the alternative successful use of cyclohexane, which we have recently reported for several amino acid benzyl esters, is inapplicable or not very efficient for ‘problematic’ amino acid such as tryptophan, arginine, and methionine, for which, indeed, the simple Fischer–Speier esterification is not described or poorly exemplified in the literature. Therefore, more polar solvents, in particular the green ethers CPME, TAME, and Me-THF, were selected and first considered for the preparation of methionine benzyl ester, previously accomplished in cyclohexane with modest yield. After discarding CPME and TAME, because causing racemization and decomposing under acidic conditions, respectively, we focused on Me-THF. In this ether, the benzyl esters of Met, Arg, and Trp could be obtained in good yield and, as proved by chiral HPLC or H NMR analysis, enantiomerically pure. The procedure was successfully extended to proline benzyl ester, which could be prepared enantiomerically pure and in quantitative yield both in cyclohexane and in Me-THF, thus avoiding the recently reported use of carbon tetrachloride.
Synthesis of Met-enkephalin by solution-phase peptide synthesis methodology utilizing para-toluene sulfonic acid as N-terminal masking of l-methionine amino acid
Khan, Riaz A.
, p. 884 - 888 (2016/11/11)
The Met-enkephalin, Tyr-Gly-Gly-Phe-Met, was synthesized by the solution-phase synthesis (SPS) methodology employing -OBzl group as carboxyls' protection, while the t-Boc groups were employed for the N-terminal α-amines' protection for the majority of the amino acids of the pentapeptide sequence. The l-methionine (l-Met) amino acid was used as PTSA.Met-OBzl obtained from the simultaneous protection of the α-amino, and carboxyl group with para-toluene sulfonic acid (PTSA) and as-OBzl ester, respectively in a C-terminal start of the 2?+?2?+?1 fragments condensation convergent synthetic approach. The protection strategy provided a short, single-step, simultaneous, orthogonal, nearly quantitative, robust, and stable process to carry through the protected l-methionine and l-phenylalanine coupling without any structural deformities during coupling and workups. The structurally confirmed final pentapeptide product was feasibly obtained in good yields through the current approach.
TRANSFORMATION OF GLYCYRRHIZIC ACID IV. SYNTHESIS OF TRITERPENE GLYCOPEPTIDES
Baltina, L. A.,Ryzhova, S. A.,Vasil'eva, E. V.,Tolstikov, G. A.
, p. 40 - 46 (2007/10/02)
The synthesis has been carried out of new triterpene glycopeptides, derivatives of β-glycyrrhizic acid, using benzyl (or 4-nitrobenzyl) esters of L-amino acids.Activation of the carboxyl groups of the glycoside was effected using N-hydroxy-benzotriazole-N,N'-dicyclohexylcarbodiimide.Deblocking of the compounds obtained was carried out by catalytic hydrogenolysis over Pd/C.Keywords: β-glycyrrhizic acid, glycopeptides
