Methadone conformation and opioid activity

Stereochemical basis for a unified structure activity theory of aromatic and heterocyclic rings in selected opioids and opioid peptides

This paper presents a novel unified theory of the structure activity relationship of opioids and opioid peptides. It is hypothesized that a virtual or known heterocyclic ring exists in all opioids which have activity in humans, and this ring occupies relative to the aromatic ring of the drug, approximately the same plane in space as the piperidine ring of morphine. Since the rings of morphine are rigid, and the aromatic and piperidine rings are critical structural components for morphine's analgesic properties, the rigid morphine molecule allows for approximations of the aromatic and heterocyclic relationships in subsequent drug models where bond rotations are common. This hypothesis and five propositions are supported by stereochemistry and experimental observations.Proposition #1 The structure of morphine provides a template. Proposition #2 Steric hindrance of some centric portion of the piperidine ring explains antagonist properties of naloxone, naltrexone and alvimopam. Proposition #3 Methadone has an active conformation which contains a virtual heterocyclic ring which explains its analgesic activity and racemic properties. Proposition #4 The piperidine ring of fentanyl can assume the morphine position under conditions of nitrogen inversion. Proposition #5 The first 3 amino acid sequences of beta endorphin (l-try-gly-gly) and the active opioid dipeptide, l-tyr-pro, (as a result of a peptide turn and zwitterion bonding) form a virtual piperazine-like ring which is similar in size, shape and location to the heterocyclic rings of morphine, meperidine, and methadone. Potential flaws in this theory are discussed.This theory could be important for future analgesic drug design.

Naturally occurring antinociceptive substances from plants

Despite the progress that has occurred in recent years in the development of therapy, there is still a need for effective and potent analgesics, especially for the treatment of chronic pain. One of the most important analgesic drugs employed in clinical practice today continues to be the alkaloid morphine. In this review, emphasis will be given to the important contribution and the history of Papaver somniferum, Salix species, Capsicum species and Cannabis sativa in the development of new analgesics and their importance in the understanding of the complex pathways related to electrophysiological and molecular mechanisms associated with pain transmission. Recently discovered antinociceptive substances include alkaloids, terpenoids and flavonoid. Plant-derived substances have, and will certainly continue to have, a relevant place in the process of drug discovery, particularly in the development of new analgesic drugs.

Physico-chemical properties of prostaglandins and related pharmacological compounds. A theoretical study on conformational related activity

Thromboxane A2, prostaglandin H2, a series of chemically stable cyclic endoperoxide analogues (U 46619, U 44069, ONO 11113, 9, 11, diazo PGH2 and SQ 26655) and different isomers of SQ 26655 were analysed for their spatial configuration by conformational analysis in a simulated membrane-water interface environment with a "structure tree" procedure already described for prostaglandins, leukotrienes and lipoxins. The conformers derived from the structure tree and with a high probability of existence are presented. A new method allows one to visualize the surface charge density of the calculated molecules. The spatial configuration and the surface charge density of each molecule are compared to their known order of competition binding to the putative TXA2/PGH2 receptor of platelets. The conformational and charge density analysis merely shows that the different stereochemistry of these molecules lead to spatial conformation, that mimics (agonists), or that are far from (antagonists) the TXA2/PGH2 conformation.