(4S)-4-mercapto-L-proline hydrochloride

Chronic pain conditions such as low back pain and osteoarthritis are the most prominent causes of disability worldwide. Morphine and other opioid drugs are the gold standard treatment for severe pain, including surgical pain, but the use of these drugs for chronic pain is limited largely because long term use of these drugs is associated with drug abuse and hyperalgesia which produces a negative impact on the treatment. Non-addictive treatments for chronic pain are, therefore, highly needed. Commonly used opioid drugs activate mu opioid receptors, resulting in an inhibition of tonic activity of nociceptive neurons. The rewarding effects of opioid drugs are also mediated via activation of mu opioid receptors and inhibition of GABA mediated control of the activity of dopamineregic neurons. Enhanced glutamate release and greater activity of NMDA glutamate receptors is linked to the hyperalgesic effects of opioid drugs. Evidence suggests that activation of serotonin (5-hydroxytryptamine; 5-HT)-1 A receptors modulates dopamine neurotransmission to inhibit rewarding effects of drugs of abuse. Activation of these receptors inhibits glutamate release from the sensory neurons to reduce pain transmission. To help develop strategies for improving therapeutics in chronic pain, and draw research interest in the synthesis of non-addictive opioid drugs which do not predispose to hyperalgesia, the present article concerns the potential mechanism involved in 5-HT-1 A receptor mediated inhibition of pain and reward.

As part of our ongoing efforts to identify novel ligands for the metabotropic glutamate 2 and 3 (mGlu2/3) receptors, we have incorporated substitution at the C3 and C4 positions of the (1S,2R,5R,6R)-2-amino-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid scaffold to generate mGlu2/3 antagonists. Exploration of this structure-activity relationship (SAR) led to the identification of (1S,2R,3S,4S,5R,6R)-2-amino-3-[(3,4-difluorophenyl)sulfanylmethyl]-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid hydrochloride (LY3020371·HCl, 19f), a potent, selective, and maximally efficacious mGlu2/3 antagonist. Further characterization of compound 19f binding to the human metabotropic 2 glutamate (hmGlu2) site was established by cocrystallization of this molecule with the amino terminal domain (ATD) of the hmGlu2 receptor protein. The resulting cocrystal structure revealed the specific ligand-protein interactions, which likely explain the high affinity of 19f for this site and support its functional mGlu2 antagonist pharmacology. Further characterization of 19f in vivo demonstrated an antidepressant-like signature in the mouse forced-swim test (mFST) assay when brain levels of this compound exceeded the cellular mGlu2 IC50 value.

Solution-phase combinatorial synthesis of (2S,4S)-4-acylamino-5-oxopyrrolidine-2-carboxamides was studied. First, di-tert-butyl (2S,4S)-4-amino-5-oxopyrrolidine-1,2-dicarboxylate hydrochloride was prepared as the key intermediate in five steps from (S)-pyroglutamic acid. Acylation of the amino group followed by acidolytic deprotection gave (2S,4S)-4-acylamino-5-oxopyrrolidine-2-carboxylic acids, which were then coupled with amines to furnish a library of (2S,4S)-4-acylamino-5-oxopyrrolidine-2-carboxamides. Four coupling reagents, BPC, EEDQ, TBTU, and PFTU, were tested for the amidation reactions in the final step. Amidations with EEDQ and TBTU led to the desired carboxamides. On the other hand, BPC and PFTU were not suited, since diketopiperazines were sometimes obtained instead of the desired carboxamides.