Synthesis and pharmacological evaluation of novel octahydro-1H-pyrido[1,2-a]pyrazine as mu-opioid receptor antagonists

Recent Progress in Heterocycle Synthesis: Cyclization Reaction with Pyridinium and Quinolinium 1,4-Zwitterions

Heteroarene 1, n-zwitterions are powerful and versatile building blocks in the construction of heterocycles and have received increasing attention in recent years. In particular, pyridinium and quinolinium 1,4-zwitterions have been widely studied and used in a variety of cyclization reactions due to their air stability, ease of use, and high efficiency. Sulfur- and nitrogen-based pyridinium and quinolinium 1,4-zwitterions, types of emerging heteroatom-containing synthons, have attracted much attention from chemists. These 1,4-zwitterions, which contain multiple reaction sites, have been successfully used in the synthesis of three- to eight-membered cyclic compounds over the last decade. In this review, we present the exciting progress made in the field of cyclization reactions of sulfur- and nitrogen-based pyridinium and quinolinium 1,4-zwitterions. Moreover, the mechanistic insights, the transition states, some synthetic applications, and the challenges and opportunities are also discussed. We hope to provide an overview for synthetic chemists who are interested in the heterocycle synthesis from cyclization reaction with pyridinium and quinolinium 1,4-zwitterions pyridinium and quinolinium 1,4-zwitterions.

Synthesis of 2,3-dicyanopyrazine and ethyl 5-amino-4,6-dicyanobiphenyl-3-carboxylate derivatives from ethyl aroylpyruvates

Reactions of ethyl 4-aryl-2,4-dioxobutanoates1a–cat ambient temperature with diaminomaleonitrile in glacial acetic acid and with malononitrile in ethanol/H2O (1:1) led to the formation of 5-(2-aryl-2-oxoethyl)-6-oxo-1,6-dihydropyrazine-2,3-dicarbontrile2a–cand ethyl 5-amino-4,6-dicyanobiphenyl-3-carboxylate derivatives3a–c, respectively.

μ Opioid receptor: novel antagonists and structural modeling

The μ opioid receptor (MOR) is a prominent member of the G protein-coupled receptor family and the molecular target of morphine and other opioid drugs. Despite the long tradition of MOR-targeting drugs, still little is known about the ligand-receptor interactions and structure-function relationships underlying the distinct biological effects upon receptor activation or inhibition. With the resolved crystal structure of the β-funaltrexamine-MOR complex, we aimed at the discovery of novel agonists and antagonists using virtual screening tools, i.e. docking, pharmacophore- and shape-based modeling. We suggest important molecular interactions, which active molecules share and distinguish agonists and antagonists. These results allowed for the generation of theoretically validated in silico workflows that were employed for prospective virtual screening. Out of 18 virtual hits evaluated in in vitro pharmacological assays, three displayed antagonist activity and the most active compound significantly inhibited morphine-induced antinociception. The new identified chemotypes hold promise for further development into neurochemical tools for studying the MOR or as potential therapeutic lead candidates.

The discovery and development of the N-substituted trans-3,4-dimethyl-4-(3'-hydroxyphenyl)piperidine class of pure opioid receptor antagonists

N-Substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines are a class of pure opioid receptor antagonists with a novel pharmacophore. This opioid receptor antagonist pharmacophore was used as a lead structure to design and develop several interesting and useful opioid receptor antagonists. In this review we describe: 1) early SAR studies that led to the discovery of LY255582 and analogues that are nonselective opioid receptor antagonists developed for the treatment of obesity; 2) the discovery and commercialization of LY246736 (alvimopan; ENTEREG®), a peripherally selective opioid receptor antagonist that accelerates the time to upper and lower GI recovery following surgeries that include partial bowel resection with primary anastomosis; and 3) the discovery and development of the potent and selective κ opioid receptor antagonist JDTic and analogues as potential pharmacotherapies for treating depression, anxiety, and substance abuse (nicotine, alcohol, and cocaine). In addition, the use of JDTic for obtaining the X-ray structure of the human κ opioid receptor is discussed.

Opioid receptors and the discriminative stimulus effects of ethanol in squirrel monkeys: Mu and delta opioid receptor mechanisms

Mu and delta opioid receptors modulate the reinforcing effects of ethanol, however, their role in the subjective effects of ethanol is not well understood. This study evaluated the contribution of mu and delta opioid receptors to the subjective effects of ethanol using drug discrimination procedures. Monkeys were trained to discriminate ethanol from saline under a schedule of food delivery. In tests, ethanol engendered increases in drug-lever responding, reaching a maximum of >80%. The mu opioid receptor agonists fentanyl and buprenorphine and the delta opioid receptor agonists SNC 80 and SNC 162 did not substitute for the discriminative stimulus effects of ethanol. As pretreatments, the full agonists fentanyl and SNC 80 enhanced the effects of low doses of ethanol and fentanyl attenuated the effects of the ethanol training dose. Although the possibility of pharmacological antagonism of the effects of ethanol cannot be ruled out, a more likely alternative is that the diminished effects of ethanol were due to perceptual masking of the ethanol stimulus. In contrast, the partial agonists buprenorphine and SNC 162 did not alter ethanol's effects. Finally, the discriminative stimulus effects of ethanol were attenuated following administration of presumably mu-selective doses of the antagonist naltrexone, but not after administration of the delta opioid receptor antagonist naltrindole. The ability of naltrexone to block the discriminative stimulus effects of ethanol likely reflects its capacity to attenuate ethanol-induced increases in endogenous opioids, in particular beta-endorphin, because attenuation of the ethanol stimulus was not accompanied by significant suppression of response rate.

Synthesis of hydroxylated bicyclic amino acids from L-tyrosine: octahydro-1H-indole carboxylates

A stereoselective approach to polyhydroxylated L-Choi derivatives has been developed. The oxidative cyclization of L-tyrosine was optimized to avoid partial racemization and to allow a more efficient scale-up.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).