Plight of CORMs: The unreliability of four commercially available CO-releasing molecules, CORM-2, CORM-3, CORM-A1, and CORM-401, in studying CO biology

Carbon monoxide (CO) is an endogenously produced gaseous signaling molecule with demonstrated pharmacological effects. In studying CO biology, three delivery forms have been used: CO gas, CO in solution, and CO donors of various types. Among the CO donors, four carbonyl complexes with either a transition metal ion or borane (BH3) (termed CO-releasing molecules or CORMs) have played the most prominent roles appearing in over 650 publications. These are CORM-2, CORM-3, CORM-A1, and CORM-401. Intriguingly, there have been unique biology findings that were only observed with these CORMs, but not CO gas; yet these properties were often attributed to CO, raising puzzling questions as to why CO source would make such a fundamental difference in terms of CO biology. Recent years have seen a large number of reports of chemical reactivity (e.g., catalase-like activity, reaction with thiol, and reduction of NAD(P)+) and demonstrated CO-independent biological activity for these four CORMs. Further, CORM-A1 releases CO in an idiosyncratic fashion; CO release from CORM-401 is strongly influenced or even dependent on reaction with an oxidant and/or a nucleophile; CORM-2 mostly releases CO2, not CO, after a water-gas shift reaction except in the presence of a strong nucleophile; and CORM-3 does not release CO except in the presence of a strong nucleophile. All these beg the question as to what constitutes an appropriate CO donor for studying CO biology. This review critically summarizes literature findings related to these aspects, with the aim of helping result interpretation when using these CORMs and development of essential criteria for an appropriate donor for studying CO biology.

Polypeptoid brushes by surface-initiated polymerization of N-substituted glycine N-carboxyanhydrides

Polypeptoid brushes were synthesized by surface-initiated polymerization of N-substituted glycine N-carboxyanhydrides on self-assembled amine monolayers. Using the presented grafting-from approach, polypeptoid brush thicknesses of approximately 40 nm could be obtained as compared to previously reported brush thicknesses of 4 nm. Moreover, hydrophilic, hydrophobic and amphiphilic polymer brushes were realized which are expected to have valuable applications as nonfouling surfaces and as model or references systems for surface grafted polypeptides.

Peptoid-Peptide hybrid ligands targeting the polo box domain of polo-like kinase 1

We replaced the amino terminal Pro residue of the Plk1 polo-box-domain-binding pentapeptide (PLHSpT) with a library of N-alkyl-Gly "peptoids", and identified long-chain tethered phenyl moieties giving greater than two-orders-of-magnitude affinity enhancement. Further simplification by replacing the peptoid residue with appropriate amides gave low-nanomolar affinity N-acylated tetrapeptides. Binding of the N-terminal long-chain phenyl extension was demonstrated by X-ray co-crystal data.

Solid-phase synthesis of N-substituted glycine oligomers (alpha-peptoids) and derivatives

Peptoids (N-substituted polyglycines and extended peptoids with variant backbone amino-acid monomer units) are oligomeric synthetic polymers that are becoming a valuable molecular tool in the biosciences. Of particular interest are their applications to the exploration of peptoid secondary structures and drug design. Major advantages of peptoids as research and pharmaceutical tools include the ease and economy of synthesis, highly variable backbone and side-chain chemistry possibilities. At the same time, peptoids have been demonstrated as highly active in biological systems while resistant to proteolytic decay. This review with 227 references considers the solid-phase synthetic aspects of peptoid preparation and utilization up to 2010 from the instigation, by R. N. Zuckermann et al., of peptoid chemistry in 1992.

Identification of N-ethylglycine in urine of cancer patients with metastatic bone disease

BACKGROUND

Previously, a HPLC method for the determination of N-terminal prolyl dipeptides, proline and hydroxyproline in urine with fluorescence detection after pre-column derivatization with 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride (DMS-Cl) [Inoue H, Iguchi H, Kono A, Tsuruta Y. Highly sensitive determination of N-terminal prolyl dipeptides, proline and hydroxyproline in urine by high-performance liquid chromatography using a new fluorescent labelling reagent, 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride. J Chromatogr 1999;724:221-230] was developed to study the relation between those analytes and bone diseases. When the urinary analytes were measured, a large peak due to an unknown substance was recognized in the chromatograms of cancer patients with metastatic bone disease, although it was scarcely present in normal subjects. In this study, we identified the unknown substance.

METHODS

The fluorescent fraction based on the unknown substance was collected using HPLC and the structure of the fluorescence product was analyzed with MS, (1)H NMR and (13)C NMR.

RESULTS

The fluorescence product based on the unknown substance was established to be a DMS-derivative of N-ethylglycine.

CONCLUSIONS

Excretion of N-ethylglycine in the urine of cancer patients with metastatic bone disease is recognized, although N-ethylglycine is scarcely excreted in the urine of normal subjects.

Potent antibacterial lysine-peptoid hybrids identified from a positional scanning combinatorial library

In this paper, we describe the synthesis and screening of a biased positional scanning library made up of peptoids (N-alkylglycines) and lysines. The library consisted of 100 mixtures divided into four sub-libraries; OXXXKKK, XOXXKKK, XXOXKKK, and XXXOKKK, O being a defined peptoid building block and X a mixture of 25 peptoid building blocks. A theoretical number of 390,625 compounds were synthesized. The compound mixtures were screened against the American Type Culture Collection (ATCC) Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 bacterial strains, and the cytotoxic activities were assessed using a human blood hemolytic assay. The results from each sub-library were examined to identify the most potent amine at each position. On the basis of this knowledge eight new lysine-peptoid hybrids were synthesized and tested in the biological assays. One compound in particular, [N-(cyclohexylmethyl)glycyl]-[N-(1-methylhexyl)glycyl]-[N-(4-methylbenzyl)glycyl]-[N-(2-(3-chlorophenyl)ethyl)glycyl]-lysyl-lysyl-lysine amide, showed high antibacterial activity and low toxicity toward red blood cells.

Protein "fingerprinting" in complex mixtures with peptoid microarrays

We report here that microarrays comprised of several thousand peptoids (oligo-N-substituted glycines) are useful tools for the identification of proteins via a "fingerprinting" approach. By using maltose-binding protein, glutathione S-transferase, and ubiquitin, a specific and highly reproducible pattern of binding was observed when fluorescently labeled protein was hybridized to the array. A similar pattern was obtained when binding of an unlabeled protein to the array was visualized by secondary hybridization of a labeled antibody against that protein, showing that native proteins can be identified without the requirement for prior chemical labeling. This work suggests that small-molecule microarrays might be used for more complex fingerprinting assays of potential diagnostic value.

Chemo-enzymatic synthesis of N-arachidonoyl glycine

N-Arachidonoyl glycine was synthesized in a chemo-enzymatic process where glycine tert -butyl ester was acylated by arachidonic acid and the resulted ester was then de-protected to give the final product. Among various lipases tested and chosen for their ability to cleave fatty amides, that from Candida antarctica B gave the best results resulting in a 39% hydrolysis after 24 h. This enzyme was then used for the reverse N-acylation synthesis and gave a 75% product formation after 24 h using methyl ester of arachadonic acid as acyl donor and acetonitrile as solvent. Direct acylation of glycine gave less than 10% yield.

Synthesis, conformation and biological activity of dermorphin and deltorphin I analogues containingN-alkylglycine in place of residues in position 1, 3, 5 and 6

Syntheses are described of new dermorphin and [D-Ala2]deltorphin I analogues in which the phenylalanine, the tyrosine or the valine residues have been substituted by the corresponding N-alkylglycine residues. Structural investigations by CD measurements in different solvents and preliminary pharmacological experiments were carried out on the resulting peptide-peptoid hybrids. The contribution from aromatic side chain residues is prominent in the CD spectra of dermorphin analogues and the assignment of a prevailing secondary structure could be questionable. In the CD spectra of deltorphin analogues the aromatic contribution is lower and the dichroic curves indicate the predominance of random conformer populations. The disappearance of the aromatic contribution in the [Ntyr1,D-Ala2]-deltorphin spectrum could be explained in terms of high conformational freedom of the N-terminal residue. The kinetics of degradation of the synthetic peptoids digestion by rat and human plasma enzymes were compared with that of [Leu5]-enkephalin. The binding to opioid receptors was tested on crude membrane preparations from CHO cells stably transfected with the mu- and delta-opioid receptors. The biological potency of peptoids was compared with that of dermorphin in GPI preparations and with that of deltorphin I in MVD preparations. All the substitutions produced a dramatic decrease in the affinity of the peptide-peptoid hybrids for both the mu- and delta-opioid receptors. Nval5 and/or Nval6 containing hybrids behaved as mu-opioid receptor agonists and elicit a dose-dependent analgesia (tail-flick test) when injected i.c.v. in rats.