Synthesis and evaluation of L-cystathionine as a standard for amino acid analysis.

L-Cystathionine is a key nonprotein amino acid related to metabolic conditions. The quantitative determination of L-cystathionine in physiological fluids by amino acid analysis is important for clinical diagnosis; however, certified reference material for L-cystathionine with satisfactory purity, content, and quantity has been unavailable until recently. Consequently, a practical and simple method for the preparation of L-cystathionine was examined, which involves thioalkylation of N-tert-butoxycarbonyl-L-cysteine tert-butyl ester, derived from L-cystine, with (2S)-2-(tert-butoxycarbonyl)amino-4-iodobutanoic acid tert-butyl ester, derived from L-aspartic acid, to obtain L-cystathionine with protecting groups, followed by single-step deprotection under mild conditions. This method produces L-cystathionine in high purity (99.4%) and having sufficient percentage content according to amino acid analysis, which could be used as a standard for the amino acid analysis of physiological fluids.

Total Chemical Synthesis of an Intra-A-Chain Cystathionine Human Insulin Analogue with Enhanced Thermal Stability.

Despite recent advances in the treatment of diabetes mellitus, storage of insulin formulations at 4 °C is still necessary to minimize chemical degradation. This is problematic in tropical regions where reliable refrigeration is not ubiquitous. Some degradation byproducts are caused by disulfide shuffling of cystine that leads to covalently bonded oligomers. Consequently we examined the utility of the non-reducible cystine isostere, cystathionine, within the A-chain. Reported herein is an efficient method for forming this mimic using simple monomeric building blocks. The intra-A-chain cystathionine insulin analogue was obtained in good overall yield, chemically characterized and demonstrated to possess native binding affinity for the insulin receptor isoform B. It was also shown to possess significantly enhanced thermal stability indicating potential application to next-generation insulin analogues.

A facile synthesis of differently protected cystathionines in aqueous solutions.

A simple method for the synthesis of differently protected cystathionines is described. Reaction of γ- bromohomoalanine with cysteine derivatives in an ethyl acetate/water two-phase system, which contains TBAHS and NaHCO3, led to the desired protected cystathionines in very high to excellent yields. Apart from the high yields, the mild conditions and the ease of conducting the reactions are also attractive features for this procedure.

Novel thiol- and thioether-containing amino acids: cystathionine and homocysteine families.

Natural L-homocysteine and L,L-cystathionine, along with a series of unnatural analogues, have been prepared from L-aspartic and L-glutamic acid. Manipulation of the protected derivatives provided ω-iodoamino acids, which were used in thioalkylation reactions of sulfur nucleophiles, such as the ester of L-cysteine and potassium thioacetate.

Synthesis of optically active homocysteine from methionine and its use in preparing four stereoisomers of cystathionine.

In order to synthesize four stereoisomers of cystathionine (CYT), D- and L-homocysteines (D- and L-Hcy) were synthesized from methionine (Met) by a facile procedure. L-Met was reacted with dichloroacetic acid in concentrated hydrochloric acid under reflux to give (4S)-1,3-thiazane-2,4-dicarboxylic acid hydrochloride [(4S)-TDC.HCl]. L-Hcy was obtained by treatment of (4S)-TDC.HCl with hydroxylamine. D-Hcy was also synthesized from D-Met via (4R)-TDC.HCl intermediate. The obtained D- and L-Hcy were condensed with (R)- and (S)-2-amino-3-chloropropanoic acid hydrochlorides under alkaline conditions to give four stereoisomers of CYT.