Arthur A. Patchett

A Receptor in Pituitary and Hypothalamus That Functions in Growth Hormone Release

Small synthetic molecules termed growth hormone secretagogues (GHSs) act on the pituitary gland and the hypothalamus to stimulate and amplify pulsatile growth hormone (GH) release. A heterotrimeric GTP-binding protein (G protein)-coupled receptor (GPC-R) of the pituitary and arcuate ventro-medial and infundibular hypothalamus of swine and humans was cloned and was shown to be the target of the GHSs. On the basis of its pharmacological and molecular characterization, this GPC-R defines a neuroendocrine pathway for the control of pulsatile GH release and supports the notion that the GHSs mimic an undiscovered hormone.

Antibacterial Agents That Inhibit Lipid A Biosynthesis

Lipid A constitutes the outer monolayer of the outer membrane of Gram-negative bacteria and is essential for bacterial growth. Synthetic antibacterials were identified that inhibit the second enzyme (a unique deacetylase) of lipid A biosynthesis. The inhibitors are chiral hydroxamic acids bearing certain hydrophobic aromatic moieties. They may bind to a metal in the active site of the deacetylase. The most potent analog (with an inhibition constant of about 50 nM) displayed a minimal inhibitory concentration of about 1 microgram per milliliter against Escherichia coli, caused three logs of bacterial killing in 4 hours, and cured mice infected with a lethal intraperitoneal dose of E. coli.

A role for the melanocortin 4 receptor in sexual function

By using a combination of genetic, pharmacological, and anatomical approaches, we show that the melanocortin 4 receptor (MC4R), implicated in the control of food intake and energy expenditure, also modulates erectile function and sexual behavior. Evidence supporting this notion is based on several findings: (i) a highly selective non-peptide MC4R agonist augments erectile activity initiated by electrical stimulation of the cavernous nerve in wild-type but not Mc4r-null mice; (ii) copulatory behavior is enhanced by administration of a selective MC4R agonist and is diminished in mice lacking Mc4r; (iii) reverse transcription (RT)-PCR and non-PCR based methods demonstrate MC4R expression in rat and human penis, and rat spinal cord, hypothalamus, brainstem, pelvic ganglion (major autonomic relay center to the penis), but not in rat primary corpus smooth muscle cavernosum cells; and (iv) in situ hybridization of glans tissue from the human and rat penis reveal MC4R expression in nerve fibers and mechanoreceptors in the glans of the penis. Collectively, these data implicate the MC4R in the modulation of penile erectile function and provide evidence that MC4R-mediated proerectile responses may be activated through neuronal circuitry in spinal cord erectile centers and somatosensory afferent nerve terminals of the penis. Our results provide a basis for the existence of MC4R-controlled neuronal pathways that control sexual function.

Chapter 26. Privileged structures — An update

Publisher Summary This chapter presents an overview of privileged structures. The term “privileged structure” was introduced by B. Evans in describing development of benzodiazepine-based CCK-A antagonists from the natural product lead asperlicin. A privileged structure such as a benzodiazepine was defined as “a single molecular framework able to provide ligands for diverse receptors…” Benzodiazepines are found in several types of central nervous system (CNS) agents and are in ligands of both ion channel and G-protein coupled receptors (GPCRs). Many of the privileged structures in GPCR ligands are found in enzyme inhibitors. Examples include benzodiazepine-containing K-secretase inhibitors and farnesyl transferase inhibitors including the tricycle-based SCH-66336 and the tetrahydrobenzodiazepine. Some examples of benzodiazepines in ion channel ligands include the delayed rectifier K+ current modulator. The chapter focuses on privileged structure based ligands of GPCRs. An overview of privileged structure based antagonists is presented and peptidomimetic GPCR agonists are discussed. An overview of agonists via privileged structure modification is presented and examples of peptidyl privileged structure agonists are presented.

Phosphonomycin: Structure and Synthesis

Synthesis and resolution of the antibiotic phosphonomycin are described. The structure is (—)(IR, 2S)-1,2-epoxypropylphosphonic acid.

Growth Hormone Releasing Substances: Types and Their Receptors

A series of structurally diverse growth hormone (GH) releasing substances have been synthesized that are distinct from the naturally occurring GH releasing hormone (GHRH). These synthetic molecules range from the family of GH releasing peptides and mimetics such as MK-0677. The physiological importance of these molecules and their receptor is exemplified by studies in the elderly. For example, when MK-0677 was administered chronically to 70- to 90-year-old subjects, once daily, the age-related reduced amplitude of GH pulses was reversed to that of the physiological profile typical of young adults. In 1996, the synthesis of 35S-MK-0677 was reported and used as a ligand to characterize a common receptor (GH secretagogue receptor [GHS-R]) for the GH releasing substances. The GHS-R is distinct from the GHRH receptor. Subsequently, the GHS-R gene was cloned and shown to encode a unique G-protein coupled receptor with a deduced protein sequence that was 96% identical in human and rat. Because of the physiological importance of the GHS-R, a search for family members (FMs) was initiated and its molecular evolution investigated. Three FMs GPR38, GPR39 and FM3 were isolated from human genomic libraries. To accelerate the identification of other FMs, a vertebrate organism with a compact genome distant in evolutionary terms from humans was exploited. The pufferfish (Spheroides nephelus) genome provides an ideal model for the discovery of human genes. Three distinct full-length clones encoding proteins of significant sequence identity to the human GHS-R were cloned from the pufferfish. Remarkably, the pufferfish gene with highest sequence homology to the human receptor was activated by the hexapeptide and non-peptide ligands. These intriguing results show that the structure and function of the ligand binding pocket of the human GHS-R has been highly conserved in evolution (400 million years) and strongly suggests that an endogenous natural ligand has been conserved. This new information is consistent with a natural ligand for the GHS-R playing a fundamentally important and conserved role in physiology.

Angiotensin-converting enzyme inhibitors

Publisher Summary Angiotensin-converting enzyme (ACE) inhibitors were first studied clinically in the 1970s. ACE inhibitors were discovered by taking advantage of previous basic research on the physiology of sodium, potassium, and water homeostasis and blood pressure regulation, in a reciprocal way ACE have also advanced research in this field, and their availability has stimulated countless studies, which are being continued to this day to enrich our understanding of the RAS and its relevance to the etiology of and risk factors associated with cardiovascular and renal diseases. Their availability exemplified at the time when the power of a new discovery paradigm in which assays using molecular targets replaced the use of animal models of disease to find and perfect bioactive compounds. The ACE generates angiotensin II by removing the Cterminal dipeptide of angiotensin I. Use of ACE inhibition has not been successful in preventing restenosis after coronary dilation and has not yet been tested after stenting. It is reassuring to observe that, after learning so much from the discovery of ACE inhibitors, so many questions remain unanswered, and, therefore, so many possibilities for progress should still be achievable within the next decade.

Inhibition of thermolysin by N-carboxymethyl dipeptides

Abstract A design principle effective for generating inhibitors of angiotensin converting enzyme has been successfully extended to inhibitors of another Zn ++ endopeptidase, thermolysin. Hence, N-(1-carboxy-3-phenylpropyl)LeuTrp is found to be a potent inhibitor of thermolysin, K i ∼ 5 × 10 −8 M.

Potent, orally bioavailable somatostatin agonists: Good absorption achieved by urea backbone cyclization

Backbone cyclization of urea-based somatostatin agonists resulted in novel, orally bioavailable agonists. Binding assays confirmed that the resulting conformationally constrained cyclic ureas retained the potency of their acyclic counterparts. SAR studies subsequently led to highly potent analogs, selective for receptor subtype 2, and having good oral bioavailability.

Dipeptide mimics. Conformationally restricted inhibitors of angiotensin-converting enzyme

A series of potent inhibitors of angiotensin-converting enzyme (dipeptidyl carboxy-peptidase, E.C. 3.4.15.1) is described which addresses conformational aspects of the enzyme-inhibitor interaction. Conformational probes were derived from simple lactams containing the required recognition and binding elements. The inhibitor potencies vary with lactam ring size in a manner predicted from molecular modeling studies and help map the active site of this important enzyme.