MW-​enhanced high-​speed deprotection of Boc group using p-​TsOH and concomitant formation of N-​Me-​amino acid benzyl ester p-​TsOH salts

A high-​speed, complete deprotection of Boc group from Boc (Boc = tert-​butoxycarbonyl) amino acids and protected peptide esters employing p-​TsOH in toluene under microwave irradn. is found to be complete in 30 s. The deprotection can be carried out in methanol and acetonitrile also. Under the present conditions, C-​peptide benzyl esters and O-​benzyl ethers have been found to be stable. This has permitted us to carry out the synthesis of [Leu]​enkephalin employing the Boc​/Bzl-​group strategy. Further more, it has been found that both Nα-​Fmoc (Fmoc = 9-​fluorenylmethyloxycarbonyl) and Nα-​Z (Z = benzyloxycarbonyl) groups are completely stable. The present conditions can be extended for the concomitant removal of the Boc group and the formation of C-​benzyl amino acid esters as well. This has been utilized for the synthesis of N-​Me amino acid benzyl esters starting from Boc-​N-​Me amino acids in a single step

Synthesis of peptidyl ureas using p-​nitrophenyl (9-​fluorenylmethoxycarbonylamino)​methylcarbamate derivatives

Carbamates Fmoc-​NHCHRNHCO2C6H4NO2-​p (Fmoc is 9-​fluorenylmethoxycarbonyl, R is an amino acid side chain) were prepd. using isocyanates derived from Fmoc-​amino acid azides and p-​nitrophenol in the presence of an equimolar quantity of N-​ethyldiisopropylamine. The carbamates were coupled with amino acid ester hydrochlorides to afford dipeptidyl ureas

Ligand Specificity of Group I Biotin Protein Ligase of Mycobacterium tuberculosis

BACKGROUND: Fatty acids are indispensable constituents of mycolic acids that impart toughness & permeability barrier to the cell envelope of M. tuberculosis. Biotin is an essential co-factor for acetyl-CoA carboxylase (ACC) the enzyme involved in the synthesis of malonyl-CoA, a committed precursor, needed for fatty acid synthesis. Biotin carboxyl carrier protein (BCCP) provides the co-factor for catalytic activity of ACC. METHODOLOGY/PRINCIPAL FINDINGS: BPL/BirA (Biotin Protein Ligase), and its substrate, biotin carboxyl carrier protein (BCCP) of Mycobacterium tuberculosis (Mt) were cloned and expressed in E. coli BL21. In contrast to EcBirA and PhBPL, the approximately 29.5 kDa MtBPL exists as a monomer in native, biotin and bio-5'AMP liganded forms. This was confirmed by molecular weight profiling by gel filtration on Superdex S-200 and Dynamic Light Scattering (DLS). Computational docking of biotin and bio-5'AMP to MtBPL show that adenylation alters the contact residues for biotin. MtBPL forms 11 H-bonds with biotin, relative to 35 with bio-5'AMP. Docking simulations also suggest that bio-5'AMP hydrogen bonds to the conserved 'GRGRRG' sequence but not biotin. The enzyme catalyzed transfer of biotin to BCCP was confirmed by incorporation of radioactive biotin and by Avidin blot. The K(m) for BCCP was approximately 5.2 microM and approximately 420 nM for biotin. MtBPL has low affinity (K(b) = 1.06x10(-6) M) for biotin relative to EcBirA but their K(m) are almost comparable suggesting that while the major function of MtBPL is biotinylation of BCCP, tight binding of biotin/bio-5'AMP by EcBirA is channeled for its repressor activity. CONCLUSIONS/SIGNIFICANCE: These studies thus open up avenues for understanding the unique features of MtBPL and the role it plays in biotin utilization in M. tuberculosis

Hydrolysis of Cyclic Ureas under Microwave Irradiation: Synthesis and Characterization of 7,8-Diaminopelargonic Acid

A simple and efficient method for the synthesis of 7,8-diaminopelargonic acid, a key intermediate in the biotin biosynthesis pathway, is reported. The d-desthiobiotin powder was dissolved in concentrated hydrochloric acid, and the solution was exposed to microwave radiation of 2.45 GHz for varying lengths of time ranging from 60 s to 2 min. The product thus obtained was characterized by spectroscopic techniques and confirmed through bioassay. Further, the protocol was extended to the synthesis of several diamines from their corresponding cyclic ureas. The results show that the method is generally applicable and not only accelerates the hydrolysis reaction but also offers excellent yields

Fmoc-amino acid azides in peptide synthesis

1733-1735Fmoc-amino acid azides can be prepared from the corresponding acid chlorides and sodium azide. All the compounds made have been obtained as solids in good yield and purity. They are found to be shelf stable at room temperature for longer periods. Their storage at room temperature does not lead to the formation of isocyanates. Employing them as coupling agents, the synthesis of a few dipeptides is described