Peptides intermediates

Robotic peptide synthesizers are now used to automatically repeat the coupling, washing, and deprotection steps with different amino acids. Each step occurs in high yield, and mechanical losses are minimized because the peptide intermediates are never removed from the insoluble polymer until the final step. Using this procedure, up to 25 to 30 mg of a peptide with 20 amino acids can be routinely prepared. 

A van Vliet, RH Smulders, BH Rietman, GI Tesser. Protected peptide intermediates using a trityl linker on a solid support, in R Epton, ed. Innovations and Perspectives in Solid Phase Synthesis. Proceedings of the 2nd Symposium. Intercept, Andover,... 

BM Iselin, R Schwyzer. Synthese of peptide intermediates for the construction of 3-melanophore-stimulating hormone (P-MSH) of beef. I. Protected peptide sequences 1-6 and 1-7. [imide by saponification of ROCO-Asp(OMe)-] Helv Chim Acta 45, 1499, 1962. 

Multidomain synthetases can include specialized domains to modify the amino acids of peptide intermediates during chain elongation. The chemistry carried out by these domains introduces specific structural motifs, which are often important for biological activity, into the peptide natural product. A summary of additional NRPS enzyme chemistry is described below and illustrated in Figure 9. 

Binding of pyridoxal phosphate to peptide PP-42 also appears to be selective for lysine 30. As was indicated by NMR spectroscopy and UV/vis experiments, only one of three potential lysine Schiff bases appeared to form. To determine the site or sites of attachment, the aldimine peptide intermediates were reduced, proteolytically cleaved, and the fragments analyzed by mass spectroscopy. This... 

With the advent of HPLC, a new tool was born that revolutionized peptide/protein chemistry as a whole as it allowed not only purification of biologically active peptides and proteins from complex mixtures of tissue or plant extracts/231 but also allowed purification of synthetic unprotected peptide mixtures analytically and preparatively.124-261 This was particularly significant in that purity could be assessed of peptide intermediates made by the classical solution-phase methodology that promoted characterization of all intermediates, as well as the purity of final products made by the solid-phase approach of MerrifieldJ27 ... 

The template was synthesized by classical fragment condensation in solution 39114 (see Section 13.1.1.1). Briefly, the condensation of two peptide intermediates, Fmoc-A2bu(COCH2ONHAloc)-Lys(Boc)-OH and NH2-A2bu(COCH2ONHBoc)-Pro-Gly-OMe, afforded the pentapeptide Fmoc-A2bu-... 

Another major lipogenic enzyme, fatty acid synthase, is also regulated in the liver by nutritional status, insulin, glucagon and T3. Wilson et al. [78] have found that stimulation of fatty acid synthase requires both thyroid hormones and insulin (40-fold stimulation), whereas T3 or insulin alone had much smaller effects (2.5.-fold). Experiments performed in the presence or the absence of puromycin suggest that a common T3-induced peptide intermediate regulates the level of both fatty acid synthase and malic enzyme mRNAs. 

Fig. 11. Reaction scheme for (I) substrate amino acid activations and dipeptide formation, (II) racemization, and (III) N-methylation. J and E2 are symbols for enzyme activities (from peptide synthetase modules) either on the same or separate proteins. R1 and R2 are amino acid side chains, where R1 is part of the first amino acid activated by the peptide synthetase indicates the linkage between 4 -phosphopantetheinylated enzyme and the substrate or peptide intermediate. AdoMet, S-adenosylmethionine AdoHcy, S-adenosylhomocysteine...

Nunn, B. L., Norbeck, A., and Keil, R. G. (2003). Hydrolysis patterns and the production of peptide intermediates during protein degradation in marine systems. Marine Chemistry 83(1—2), 59-73. 

Figure 3 Cysteine protease and subtilisin-like protease pathways for proneuropeptide processing. Distinct cysteine protease and subtilisin-like protease pathways have been demonstrated for pro-neuropeptide processing. Recent studies have identified secretory vesicle cathepsin L as an important processing enzyme for the production of the endogenous enkephalin opioid peptide. Preference of cathepsin L to cleave at the NH2-terminal side of dibasic residue processing sites yields peptide intermediates with NH2-terminal residues, which are removed by Arg/Lys aminopeptidase. The well-established subtilisin-like protease pathway involves several prohormone convertases (PC). PC1/3 and PC2 have been characterized as neuroendocrine processing proteases. The PC enzymes preferentially cleave at the COOH-terminal side of dibasic processing sites, which results in peptide intermediates with basic residue extensions at their COOH-termini that are removed by carboxypeptidase E/H.

Narita, M., Honda, S., Umeyama, R and Obana, S. (1988). BM. Chem. Soc. Jap. 61,281 284 (1988). The solubility of peptide intermediates in organic solvents. Solubilizing ability of hexafluoro-2-propanoL... 

Its use in solution synthesis is limited by the presence of sulfur-containing anoino acid residues as these poison metal catalysts, albeit methods have been proposed that partially overcome this serious drawback (see Section 2.1.1.1.1.1.3.1). This linoitation is also bypassed in cases where the target peptide molecule permits acidolysis with strong acids (HBr/AcOH or HF). As an additional limitation, the saponification of Al -Z-protected peptide esters under drastic conditions, such as those required for longer peptide intermediates, was found to induce decomposition of the Al -Z moiety with generation of N-ternninal hydantoins. ... 

In general the /er/-butyl esters, as used in the Z/tBu strategy in solution, are stable towards hydrazinolysis. Therefore, peptide intermediates containing Glu(OtBu) residues are readily converted into the corresponding hydrazides, although in the case of Asp(OtBu) residues controversial results were reported depending upon the reaction conditions and apparently even upon the peptide sequence.t In the case of the base-sensitive Asp-Gly and Asp-Ser sequences the tert-butyl ester protection does not prevent aspartimide formation similarly, in cases of Asn-Gly sequences a P transpeptidation on treatment with hydrazine was found to occur although to a lower extent. 

The participation of a nucleotide-activated disaccharide and UDP-activated peptide intermediates are unique features of pseudomurein biosynthesis. Usually, oligosaccharide precursors of bacterial cell-wall polymers are formed at the lipid stage [38,44] and amino acids carrying a nucleotide residue at the. /V -amino group have not been found in nature so far. The distinct differences between the two biosynthetic routes support the hypothesis that murein and pseudomurein represent independent inventions made after the domains bacteria and archaea had been separated from each other during evolution [40,46]. 

To date, only two purely NRPS biosynthetic machineries have been reported from myxobacteria. The first NRPS pathway to be characterized (and the first myxobacterial gene cluster to be identified) directs the biosynthesis of the DNA-binding antibiotic and antitumor agent saframycin Mxl 30 in M. xanthus Its heterocyclic quinone structure originates from a linear peptide intermediate 27 (Ala-Gly-Tyr-Tyr), which is synthesized by a tetramodular assembly line composed of two multifunctional NRPSs, SafA and SafB (Figure 10). It is likely that the tyrosine precursor is modified to 3-hydroxy-5-methyl-0-methyltyrosine through hydroxylation as well as O- and C-methylation reactions, before the monomer is loaded onto the NRPS complex. Once the tetrapeptide structure (27) is constructed, chain release by the last module of the assembly line should occur. However, in SafA, the typical C-terminal TE domain is substituted with a putative... 

L-Valyl-L-valyl-L-proline was incorporated into ergocornine (135) only after breakdown into its constituent amino-acids/ These negative results have led to the suggestion that formation of the peptidic fragment and linkage with lysergic acid occurs on a multi-enzyme complex so that at no stage are there any free peptidic intermediates. 

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