Reversed Proteolysis—Proteases as Peptide Ligases

Historically, ligase activity by proteases was theoretically derived due to their catalyst nature, and it was experimentally observed as early as around 1900. Initially, the digestive proteases, such as pepsin, chymotrypsin, and trypsin were employed to perform in vitro syntheses of small peptides. Protease-catalyzed ligation is more efficient than peptide bond hydrolysis in organic solvents, representing control of the thermodynamic equilibrium. Peptide esters readily form acyl intermediates with serine and cysteine proteases, followed by peptide bond synthesis at the N-terminus of another residue. This type of reaction is under kinetic control, favoring aminolysis over hydrolysis. Although only a few natural peptide ligases are known, such as ubiquitin ligases, sortases, and legumains, the principle of proteases as general catalysts could be adapted to engineer some proteases accordingly. In particular, the serine proteases subtilisin and trypsin were converted to efficient ligases, which are known as subtiligase and trypsiligase. Together with sortases and legumains, they turned out to be very useful in linking peptides and proteins with a great variety of molecules, including biomarkers, sugars or building blocks with non-natural amino acids. Thus, these engineered enzymes are a promising branch for academic research and for pharmaceutical progress.

Synthetic Methods of Phosphonopeptides

Phosphonopeptides are phosphorus analogues of peptides and have been widely applied as enzyme inhibitors and antigens to induce catalytic antibodies. Phosphonopeptides generally contain one aminoalkylphosphonic acid residue and include phosphonopeptides with C-terminal aminoalkylphosphonic acids and phosphonopeptides with a phosphonamidate bond. The phosphonamidate bond in the phosphonopeptides is generally formed via phosphonylation with phosphonochloridates, condensation with coupling reagents and enzymes, and phosphinylation followed by oxidation. Pseudo four-component condensation reaction of amides, aldehydes, alkyl dichlorophosphites, and amino/peptide esters is an alternative, convergent, and efficient strategy for synthesis of phosphonopeptides through simultaneous construction of aminoalkylphosphonic acids and formation of the phosphonamidate bond. This review focuses on the synthetic methods of phosphonopeptides containing a phosphonamidate bond.

The Antiinflammatory Action and Pharmacokinetics of a Novel Glucosamine-based Di-Peptide Aminosugar

Purpose. We have previously shown favorable in vitro gut permeability for three novel di-peptide esters of glucosamine (GlcN) likely facilitated by the peptide transporter 1 (PepT1). Herein, we report the development of a novel assay for the determination of bioavailability of the peptide ester of interest, the anti-inflammatory properties of a glycine-valine ester derivative of GlcN (GVG) as well as its pharmacokinetics under healthy and inflammatory conditions. Methods. A pre-column derivatization (with 9-fluorenylmethoxycarbonyl) HPLC assay was developed to study bioavailability of GVG, GlcN or cleaved GlcN in the rats that were cannulated in their right jugular vein for blood collection. The compounds of interest were orally administered to both healthy and arthritic rats. Serial blood samples and urine were collected and assayed for the compounds. The stability of the GVG was also tested after incubation with the rat feces. Efficacy of GVG was tested in inflamed rats (injection of 0.2 mL of Mycobacterium butyricum in squalene) following GVG (20 and 30 mg/kg/day GlcN equivalent) or GlcN (20 and 90 mg/kg/day) administration. Arthritis index was calculated at the end of the experiment. Results. The assay was linear (ranged between 0.05-20 μg/mL) and reproducible (intra- and inter-day<10%). Among the tested compounds, only GVG showed a significantly higher plasma concentrations and urinary excretion than GlcN (≈3-fold increase). GVG showed a favorable stability in the rat feces. Adjuvant arthritis was completely prevented with doses greater than 20 mg/kg/day with GVG being 3-fold more potent than GlcN. Conclusion. The examined glycine-valine-GlcN di-peptide aminosugar is a potent anti-inflammatory compound due to its favorable properties to deliver GlcN into the systemic circulation. This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.

Identification of Self-Assembly Products of L-Valine Mediated by Phosphorus Trichloride by ESI Mass Spcetrometry

With the assistance of phosphorus trichloride, L-Valine (L-Val) was assembled into homopeptides and homocyclopeptides which were analyzed by electrospray ionization mass spectrometry (ESI-MS). On quenching with water or various alcohols, the reaction mixtures yielded the corresponding peptides or peptide esters and cyclopeptides, respectively. The formation of the products was proved by multistage electrospray ionization mass spectrometry (ESI-MS/MS).

Low Molecular Weight Opioid Peptide Esters Could be Developed as a New Class of Analgesics

Low molecular weight opioid peptide esters (OPE) could become a class of analgesics with different side effect profiles than current opiates. OPE may have sufficient plasma stability to cross the blood brain barrier (BBB), undergo ester hydrolysis and produce analgesia. OPE of dipeptides, tyr-pro and tyr-gly conjugated to ethanol have a structure similar to the anesthestic agent, etomidate. Based upon the analgesic activity of dipeptide opioids, Lipinski's criteria, and permeability of select GABA esters to cross the BBB, opioid peptides (OP) conjugated to ethanol, cholesterol or 3-glucose are lead recommendations. Preliminary animal data suggests that tyr-pro-ethyl ester crosses the BBB and unexpectedly produces hyperalgesia. Currently, there are no approved OP analgesics available for clinical use. Clinical trials of good manufacturing practice OP administered to patients suffering from chronic pain with indwelling intrathecal pumps could resolve the issue that OP may be superior to opiates and may redirect research.