Synthesis of Ethylene-Bridged (Nδ to Nω) Analogues of Arginine

Diuretic Activity of a Novel Peripherally-Restricted Orally-Active Kappa Opioid Receptor Agonist

Kappa-opioid agonists (KOAs) enhance cardiac performance, as well as reduce infarct size and prevent deleterious cardiac remodeling following myocardial infarction. Additionally, KOAs promote diuresis; however, there has been limited development of KOAs as a class due to the promotion of untoward central nervous system (CNS)-mediated side effects. Our laboratory has developed a peripherally-restricted, orally-active, KOA (JT09) for the treatment of pain and cardiovascular disease. Peripherally-restricted KOAs possess a limited side-effect profile and demonstrate potential in preventing heart failure. The aim of this study was to assess the diuretic activity of lead compound JT09 relative to vehicle control and Tolvaptan through single oral administration to adult male Sprague–Dawley rats. JT09-administered rats demonstrated significantly increased urine output relative to vehicle control. However, the effect persisted for 8 h, whereas Tolvaptan-administered rats demonstrated diuretic activity for 24 h. Relative to Tolvaptan, urine output was significantly reduced in JT09 administered animals at all-time points, suggesting that the overall diuretic effect of JT09 is less profound than Tolvaptan. Additionally, JT09-administered rats demonstrated alterations in clinical chemistry; reduced urine specific gravity; and increased urine pH relative to vehicle control. The following study establishes a preliminary diuretic profile for JT09.

Non-addictive orally-active kappa opioid agonists for the treatment of peripheral pain in rats

Addiction to conventional opioid pain analgesics is a major societal problem that is increasing at an alarming rate. New drugs to combat the effects of opioid abuse are desperately needed. Kappa-opioid agonists are efficacious in peripheral pain models but suffer from centrally-mediated effects. In this article, we discuss our efforts in developing peripheral kappa-based opioid receptor agonists that have the potential analgesic activity of opioids but do not manifest the negative side-effects of opioid use and abuse. Further, derivatives of the tetra-peptide D-Phe-D-Phe-D-Nle-D-Arg-NH2, such as CR665, exhibit high peripheral to central selectivity in analgesic models when administered intravenously (i.v.); however, they are inactive when administered orally. Application of our laboratory's proprietary non-natural amino acid technology to CR665 produced derivatives that exhibit peripheral analgesic activity when dosed orally but do not promote CNS-based effects. Lead compound JT09 activates the kappa-opioid receptor with EC50s in the low nM range, while agonist selectivity for kappa over other peripheral opioid receptors was >33,400 fold. Results indicate that JT09 is approximately as efficacious as morphine in alleviating peripheral pain, while failing to produce undesired CNS-mediated activity. Additionally, JT09 did not promote other CNS-mediated effects associated with morphine (addiction, sedation, dysphoria, tolerance, addiction). Thus, we propose that JT09 has potential for development as a novel analgesic. PERSPECTIVE: This article presents data supporting the analgesic properties of an orally available, peripherally-restricted, kappa-opioid agonist for peripheral pain. A potential out-patient pharmaceutical that acts as efficacious as morphine in alleviating peripheral pain, while failing to produce undesired CNS-mediated effects, could help reduce the current health care burden associated with prescription opioids.

Identification and functional characterization of a stable, centrally active derivative of the neurotensin (8-13) fragment as a potential first-in-class analgesic

The neurotensin hexapapetide fragment NT(8-13) is a potent analgesic when administered directly to the central nervous system but does not cross the blood-brain barrier. A total of 43 novel derivatives of NT(8-13) were evaluated, with one, ABS212 (1), being most active in four rat models of pain when administered peripherally. Compound 1 binds to human neurotensin receptors 1 and 2 with IC(50) of 10.6 and 54.2 nM, respectively, and tolerance to the compound in a rat pain model did not develop after 12 days of daily administration. When it was administered peripherally, serum levels and neurotensin receptor binding potency of 1 peaked within 5 min and returned to baseline within 90-120 min; however, analgesic activity remained near maximum for >240 min. This could be due to its metabolism into an active fragment; however, all 4- and 5-mer hydrolysis products were inactive. This pharmacokinetic/pharmacodynamic dichotomy is discussed. Compound 1 is a candidate for development as a first-in-class analgesic.

Design, synthesis, and evaluation of the antipsychotic potential of orally bioavailable neurotensin (8-13) analogues containing non-natural arginine and lysine residues

Neurotensin (NT) and its active fragment NT(8-13) elicit behavioral responses typical of clinically used antipsychotic drugs when administered directly to the brain. However, limited peptide stability and oral bioavailability have prevented these compounds from being developed as relevant pharmaceuticals. Recently, our laboratory designed and studied a first-generation NT(8-13) derivative, KK13, that elicited key pharmacokinetic and behavioral responses typical of clinically used antipsychotic drugs when administered to rats parenterally. This compound was the basis for the rational design of a series of second-generation NT(8-13) analogues (KH1-KH30) studied in this paper. Initial screening of these analogues for CNS activity by monitoring hypothermia induction after peripheral administration defined several compounds (KH11, KH24, KH26, and KH28-KH30) that warranted further investigation. Each compound maintained binding affinity for NTR(1), however, only KH24, KH26, and KH28 (as well as KK13) elicited significant hypothermic responses after oral administration. Of these, KH28 demonstrated an oral activity 3-fold greater than any other analogue; hence it was further characterized in a series of rat behavioral assays. KH28 attenuated d-amphetamine induced hyperlocomotion, a hallmark of current clinically effective antipsychotic drugs, after both IP and oral administration. In addition, tolerance to the compound did not develop after repeated daily dosing, as measured by hypothermic induction as well as attenuation of d-amphetamine induced hyperlocomotion. Finally, KH28 did not produce catalepsy, a deleterious side-effect elicited by classical antipsychotic drugs. KH28 is considered to be an ideal compound for further development as a potential novel antipsychotic.

Synthesis and analysis of potent, more lipophilic derivatives of the bradykinin B2 receptor antagonist peptide Hoe 140

Bradykinin (BK) is an endogenous peptide that has been implicated in several pathological conditions, hence antagonists of its activity have therapeutic potential. The decapeptide Hoe 140 is currently one of the best BK antagonists, but interest remains in finding even more potent compounds. A library of Hoe 140 derivatives was synthesized that incorporated non-natural analogs of the cationic, naturally occurring amino acids arginine (Arg) and lysine (Lys). The modified amino acids were designed to form enhanced ionic interactions due to an increase in local hydrophobicity, which promotes desolvation of the cation in water. The potencies of the resulting peptides were determined by competitive binding assays in human A431 cells expressing the BK B2 receptor. Two of the peptides synthesized were equipotent to Hoe 140 (IC(50s) 2.99 and 3.36 nM) and the most potent was demonstrated as a functional antagonist in vitro by blocking BK-mediated phosphorylation of mitogen-activated protein (MAP) kinases. The new derivatives are more hydrophobic than Hoe 140 and thus may exhibit changes in pharmacokinetic properties when evaluated in vivo.

Topography of the neurotensin (NT)(8-9) binding site of human NT receptor-1 probed with NT(8-13) analogs

A series of neurotensin (NT)(8-13) analogs featuring substitution of the Arg8 and/or Arg9 residues with non-natural cationic amino acids was synthesized and evaluated for binding to the human NT receptor-1 (hNTR-1). The modifications were designed to probe specific steric and electrostatic requirements in the N-terminal cationic region of NT(8-13) for receptor binding as a general evaluation of the feasibility of incorporating minor structural changes into a peptide at a crucial polar receptor binding site. Many of the non-natural amino acids are more or less isosteric to Arg but more lipophilic as a result of addition of alkyl groups or through removal or replacement of NH character with methylene or methyl substituents, whereas others vary the distance between the cation and the alpha-amino acid carbon. Substitution of Arg8 with N(G)-alkylated Arg derivatives or homolysine (Hlys) maintained the subnanomolar affinity of NT(8-13) to the hNTR-1. Position 8 incorporation of Hlys produced the most favorable primary amine side-chain substitution to date. Moderate losses in affinity observed with position 9 substitutions were attributed to adverse steric effects. Doubly substituted [Hlys8, DAB9]NT(8-13), in which DAB is 2,4-diaminobutyric acid, was also prepared and tested as the shorter side-chain of DAB is known to be favored in position 9 of NT(8-13). This analog maintained 60% of NT(8-13) binding affinity making it the most favored des-guanidinium-containing analog known. These results demonstrate that adequate receptor binding affinity can be maintained over a structural range of Arg analogs, thus providing a range of peptides expected to exhibit altered pharmacokinetic properties. From the standpoint of the hNTR-1 cationic binding sites, these results help to map out the structural stringency inherent in the formation of a tight binding complex with NT(8-13) and related analogs.

A novel approach for the solid-phase synthesis of substituted cyclic guanidines, their respective bis analogues, and N-acylated guanidines from N-acylated amino acid amides

An efficient method for the solid-phase synthesis of cyclic guanidines from N-acylated amino acid amides, bis cyclic guanidines from N-acylated dipeptides derived from orthogonally protected diamino acids, and N-acylated guanidines from disubstituted cyclic guanidines is described. The exhaustive reduction of N-acylated amino acid amides yields diamines that on treatment with cyanogen bromide lead to the formation of cyclic guanidines. Resin-bound orthogonally protected diamino acids (i.e., N(alpha)-Fmoc-N(x)-(Boc)-diamino acid, x = beta, gamma, delta, epsilon) were N-acylated following removal of the Fmoc group. Removal of the Boc functionality from the side chain then generated a primary amine. Subsequent coupling of Boc amino acids, followed by removal of the Boc group, generated dipeptides that were N-acylated. Exhaustive reduction of amide bonds of the N-acylated dipeptides generated tetraamines having four secondary amines, which upon cyclization with cyanogen bromide afforded the resin-bound trisubstituted bis cyclic guanidines. Treatment of the resin-bound disubstituted cyclic guanidines with carboxylic acids gave N-acylated guanidines. On the basis of their high yield and purity, bis cyclic guanidines derived from N(alpha)-Fmoc-N(epsilon)-Boc-lysine and N-acylated guanidines were chosen for preparation of mixture-based combinatorial libraries. Details of the preparation of these positional scanning libraries using the "libraries from libraries" concept are presented.

Design rationale, synthesis, and characterization of non-natural analogs of the cationic amino acids arginine and lysine

A series of non-natural isosteric analogs of the cationic, ion-pairing, natural amino acids arginine and lysine have been synthesized, characterized with regard to relevant physical parameters, and protected for routine inclusion in Merrifield solid-phase synthesis. The design of these molecules is based on the concept of steric inhibition of solvation, in that judicious placement of alkyl groups can destabilize aqueous ion solvation and favor ion-pairing [see Beeson & Dix (1993) J. Am. Chem. Soc. 115, 10275]. When the residues are substituted for the natural amino acids in biologically active peptides, enhanced ion-pairing of the peptides to their receptors to increase the peptides' biological activities can result. The increased lipophilicity of the non-natural residues can also improve pharmacokinetic parameters and agonist/antagonist behaviors of peptides. While the synthesis of the L-series is described, the D-isomers were also prepared using identical chemistry.