Synthesis of α-amino acids by reaction of aziridine-2-carboxylic acids with carbon nucleophiles

Investigation of β-Substitution Activity of O-Acetylserine Sulfhydrolase from Citrullus vulgaris

Pyridoxal-5'-phosphate (PLP)-dependent enzymes have garnered interest for their ability to synthesize non-standard amino acids (nsAAs). One such class of enzymes, O-acetylserine sulfhydrylases (OASSs), catalyzes the final step in the biosynthesis of l-cysteine. Here, we examine the β-substitution capability of the OASS from Citrullus vulgaris (CvOASS), a putative l-mimosine synthase. While the previously reported mimosine synthase activity was not reproducible in our hands, we successfully identified non-native reactivity with a variety of O-nucleophiles. Optimization of reaction conditions for carboxylate and phenolate substrates led to distinct conditions that were leveraged for the preparative-scale synthesis of nsAAs. We further show this enzyme is capable of C-C bond formation through a β-alkylation reaction with an activated nitroalkane. To facilitate understanding of this enzyme, we determined the crystal structure of the enzyme bound to PLP as the internal aldimine at 1.55 Å, revealing key features of the active site and providing information that may guide subsequent development of CvOASS as a practical biocatalyst.

Synthesis and physical chemical properties of 2-amino-4-(trifluoromethoxy)butanoic acid - a CF3O-containing analogue of natural lipophilic amino acids

2-Amino-2-(trifluoromethoxy)butanoic acid (O-trifluoromethyl homoserine) was synthesized as a racemate and in both enantiomeric forms. The measured pK_a and log D values establish the compound as a promising analogue of natural aliphatic amino acids.

Aqueous MW eco-friendly protocol for amino group protection

In this paper a new catalyst-free and on-water method for protection of amines and amino acids with di-tert-butyl dicarbonate, 9-fluorenylmethoxycarbonyl chloride, acetyl chloride and tosyl chloride is presented.

Synthesis of functionalized arylaziridines as potential antimicrobial agents

By using the Suzuki-Miyaura protocol, a simple straightforward synthesis of functionalized 2-arylaziridines has been developed. By means of this synthetic strategy from readily available ortho-, meta- and para-bromophenylaziridines and aryl- or heteroarylboronic acids, new aziridines could be obtained. The cross-coupling reactions occurred without ring opening of the three membered ring. Preliminary results on the antimicrobial activity of the heterosubstituted biaryl compounds have been also included.

Quantification of competing H3PO4 versus HPO3 + H2O neutral losses from regioselective 18O-labeled phosphopeptides

Abundant neutral losses of 98 Da are often observed upon ion trap CID-MS/MS of protonated phosphopeptide ions. Two competing fragmentation pathways are involved in this process, namely, the direct loss of H3PO4 from the phosphorylated residue and the combined losses of HPO3 and H2O from the phosphorylation site and from an additional site within the peptide, respectively. These competing pathways produce product ions with different structures but the same m/z values, potentially limiting the utility of CID-MS(3) for phosphorylation site localization. To quantify the relative contributions of these pathways and to determine the conditions under which each pathway predominates, we have examined the ion trap CID-MS/MS fragmentation of a series of regioselective (18)O-phosphate ester labeled phosphopeptides prepared using novel solution-phase amino acid synthesis and solid-phase peptide synthesis methodologies. By comparing the intensity of the -100 Da (-H3PO3 (18)O) versus -98 Da (-[HPO3 + H2O]) neutral loss product ions formed upon MS/MS, quantification of the two pathways was achieved. Factors that affect the extent of formation of the competing neutral losses were investigated, with the combined loss pathway predominantly occurring under conditions of limited proton mobility, and with increased combined losses observed for phosphothreonine compared with phosphoserine-containing peptides. The combined loss pathway was found to be less dominant under ion activation conditions associated with HCD-MS/MS. Finally, the contribution of carboxylic acid functional groups and backbone amide bonds to the water loss in the combined loss fragmentation pathway was determined via methyl esterification and by examination of a phosphopeptide lacking side-chain hydroxyl groups.

Ring opening of pymisyl-protected aziridines with organocuprates

The pyrimidine-2-sulfonyl (pymisyl) group is introduced as a new protecting group that can be used to activate aziridines towards ring opening. It is readily introduced and removed under mild conditions. Regioselective ring opening of pymisyl-protected 2-methyl-aziridine with organocuprates gives the corresponding sulfonamides in high yields, and the pymisyl group can subsequently be removed upon treatment with a thiolate. The versatility of this new nitrogen protecting group is illustrated with a new synthesis of Selegiline, a monoamine oxidase-B inhibitor marketed for the treatment of Parkinson's disease.

Development of chemical probes: toward the mode of action of a methylene-linked di(aryl acetate) E1

Analogues of the novel inhibitor of the PI3-K/PKB pathway, 2-[5-(2-chloroethyl)-2-acetoxy-benzyl]-4-(2-chloroethyl)-phenyl acetate (E1), have been prepared and preliminary SAR performed. This established that at least one of the chloroethyl para-substituents could be removed or modified and the ability to inhibit PKB/Akt activation retained. Synthetic methodologies were then developed to methylene-linked aryl acetates for use as molecular probes to identify the target of compound E1.