Albert Isidro-Llobet, Mercedes Alvarez,* and Fernando Albericio* Institute for Research in Biomedicine, Barcelona Science Park, Baldiri Reixac 10, 08028 Barcelona, Spain; CIBER-BBN, Networking Centre on Bioengineering, Biomaterials and Nanomedicine, Barcelona Science Park, Baldiri Reixac 10, 08028 Barcelona, Spain; Laboratory of Organic Chemistry, Faculty of Pharmacy, University of Barcelona, 08028 Barcelona, Spain; and Department of Organic Chemistry, University of Barcelona, Marti i Franques 1, 08028 Barcelona, Spain Received April 28, 2008

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Amino Acid-Protecting Groups

It is a privilege to be able to contribute to this volume in which Professor Zervas’ friends, students, and colleagues have joined together to honor him and his remarkable contributions to peptide chemistry. Although I did not know him until after his days in the Bergmann Laboratory at the Rockefeller Institute, I can claim the distinction of now working in those very same rooms that they occupied back in the mid-1930s. Like all peptide chemists, I am greatly indebted to Professor Zervas, having depended so heavily on the carbobenzoxy group and on the various modified urethan protecting groups which have been direct extensions of the revolutionary advance that Bergmann and Zervas made.

Solid-phase peptide synthesis.

Normal young adult male and female subjects were maintained on fixed dietary regimens which were either essentially normal or were semisynthetic and curtailed in methionine and choline intakes and virtually free of cystine. The subjects maintained stable weights and remained in positive nitrogen balance or within the zone of sulfur equilibrium. Choline intakes were calculated, and urinary excretions of creatinine, creatine, and sacrosine were measured. Creatinine excretions of male subjects on essentially normal diets outweighed the total intakes of labile methyl groups. Taking into account the excretions of additional methylated compounds, as judged from published values, it appears that methyl neogenesis must normally play a role in both males and females. When labile methyl intake is curtailed, de novo formation of methyl groups is quantitatively more significant than ingestion of preformed methyl moieties. On the normal diets used in these experiments, the average homocysteinyl moiety in males cycled between methionine and homocysteine at least 1.9 times before being converted to cystathionine. For females, the average number of cycles was at least 1.5. When labile methyl intake was curtailed, the average number of cycles rose to 3.9 for males and 3.0 for females under the conditions employed.

Labile methyl balances for normal humans on various dietary regimens.

We recently reviewed the status of peptide and nonpeptide agonists and antagonists for the V1a, V1b and V2 receptors for arginine vasopressin (AVP) and the oxytocin receptor for oxytocin (OT). In the present review, we update the status of peptides and nonpeptides as: (i) research tools and (ii) therapeutic agents. We also present our recent findings on the design of fluorescent ligands for V1b receptor localisation and for OT receptor dimerisation. We note the exciting discoveries regarding two novel naturally occurring analogues of OT. Recent reports of a selective VP V1a agonist and a selective OT agonist point to the continued therapeutic potential of peptides in this field. To date, only two nonpeptides, the V2/V1a antagonist, conivaptan and the V2 antagonist tolvaptan have received Food and Drug Administration approval for clinical use. The development of nonpeptide AVP V1a, V1b and V2 antagonists and OT agonists and antagonists has recently been abandoned by Merck, Sanofi and Pfizer. A promising OT antagonist, Retosiban, developed at Glaxo SmithKline is currently in a Phase II clinical trial for the prevention of premature labour. A number of the nonpeptide ligands that were not successful in clinical trials are proving to be valuable as research tools. Peptide agonists and antagonists continue to be very widely used as research tools in this field. In this regard, we present receptor data on some of the most widely used peptide and nonpeptide ligands, as a guide for their use, especially with regard to receptor selectivity and species differences.

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Oxytocin and Vasopressin Agonists and Antagonists as Research Tools and Potential Therapeutics

Oxytocin (OT) and vasopressin (AVP) mediate their biological actions by acting on four known receptors: The OT (uterine) and the AVP V(1a) (vasopressor), V(1b) (pituitary), V(2) (renal) receptors and a fifth putative AVP V(1c)? (vasodilating) receptor. This presentation will summarize some highlights of the recent progress, in the design and synthesis of selective peptide agonists, antagonists, radioiodinated ligands, fluorescent ligands and bivalent ligands for these receptors. Here we present published and unpublished pharmacological data on the most widely used agonists, antagonists and labelled ligands. The pharmacological properties of promising new selective OT antagonists and V(1b) agonists are also presented. This review should serve as a useful guide for the selection of the most appropriate ligand for a given study. The current status of non-peptide OT and AVP antagonists and agonists is also summarized. The relative merits of peptide and non-peptide AVP and OT agonists and antagonists as: (1) research tools and (2) therapeutic agents will be evaluated. Many of the receptor selective peptide agonists and antagonists from this and other laboratories are far more widely used as pharmacological tools for studies on the peripheral and central effects of OT and AVP than their non-peptide counterparts. In addition to OT and to a lesser extent AVP (pitressin), a number of OT and AVP analogues; such as carbetocin (OT agonist) dDAVP (desmopressin, V(2) agonist), terlipressin (V(1a) agonist), felypressin (V(1a) agonist) and atosiban (Tractocile OT antagonist) are also in clinical use. Despite much early promise, no non-peptide V(1a) or OT antagonists are currently in clinical trials. While a number of orally active non-peptide V(2) antagonists (Vaptans); notably, Tolvaptan, Lixivaptan and Satavaptan, are currently in Phase III clinical trials; to date, only the mixed V(2)/V(1a), antagonist Conivaptan (Vaprisol), has been approved by the US FDA for clinical use (by i.v. administration), for the treatment of euvolemic and hypervolemic hyponatremia in hospitalized patients. Promising new non-peptide V(1b) and OT antagonists, as well as non-peptide V(2) and OT agonists are now in pre-clinical development.

Peptide and non-peptide agonists and antagonists for the vasopressin and oxytocin V1a, V1b, V2 and OT receptors: research tools and potential therapeutic agents.

(1-Beta-mercapto-beta,beta-diethylpropionic acid)-8-lysine-vasopressin, a potent inhibitor of 8-lysine-vasopressin and of oxytocin.

[1-Beta-mercapto-beta,beta-pentamethylenepropionic acid]oxytocin was prepared from beta-Mpa(beta-(CH2)5)(Bzl)-Tyr(Bzl)-Ile-Gln-Asn-Cys(Bzl)-Pro-Leu-Gly-NH2 by removal of the Bzl-protecting groups with Na-NH3 followed by cyclization of the resulting disulfhydryl compound with K3Fe(CN)6.The analog was purified by desalting on Sephadex G-15 in 50% HOAc and gel filtration on Sephadex G-25 and LH-20. The protected intermediate above was synthesized from Z-Cys(Bzl)-Pro-Leu-Gly-NH2 by the stepwose p-nitrophenyl ester method using Nalpha-Boc protection at the penta-, hexa-, and octapeptide stages. The analog was found to be a potent inhibitor of the oxytocic and avian vasodepressor effects of oxytocin (pA2 values of 7.43 and 8.30, respectively) but was only a weak inhibitor of the rat pressor effect of 8-lysine-vasopressin. The rat antipressor potency of [1-deaminopenicillamine]oxytocin was also determined in this study: pA2 = 6.27. Of the alkyl-substituted 1-position analogs of oxytocin studied so far, [1-beta-mercapto-beta,beta-pentamethylenepropionic acid]oxytocin is the most potent antioxytocic agent.

[1-Beta-mercapto-beta,beta-pentamethylenepropionic acid]oxytocin, a potent inhibitor of oxytocin.

The antiphenylalanine effect of beta-2-thienylalanine for the rat.

OXIDATION IN VIVO OF THE METHYL GROUPS OF CHOLINE, BETAINE, DIMETHYLTHETIN, AND DIMETHYL-β-PROPIOTHETIN

The 220-MHz proton NMR spectra of lysine-vasopressin and some related compounds are examined in deuterated dimethyl sulfoxide to obtain structural information that must be satisfied by any proposed conformation of the molecule. This structural information is in the form of dihedral angles (for rotation about the NH-CαH bonds) from coupling constants, possible hydrogen bonding of the CONH2 and backbone amide groups from the temperature-dependence of the chemical shift, and aromatic ring-aromatic ring interaction from the effect of the magnetically anisotropic groups on the chemical shift.

M. F. Ferger

Papers

(1-Beta-mercapto-beta,beta-diethylpropionic acid)-8-lysine-vasopressin, a potent inhibitor of 8-lysine-vasopressin and of oxytocin.

[1-Beta-mercapto-beta,beta-pentamethylenepropionic acid]oxytocin, a potent inhibitor of oxytocin.

The antiphenylalanine effect of beta-2-thienylalanine for the rat.

OXIDATION IN VIVO OF THE METHYL GROUPS OF CHOLINE, BETAINE, DIMETHYLTHETIN, AND DIMETHYL-β-PROPIOTHETIN

Nuclear magnetic resonance studies of lysine-vasopressin: structural constraints.