The discovery of capsazepine, the first competitive antagonist of the sensory neuron excitants capsaicin and resiniferatoxin.

Capsaicin and resiniferatoxin are natural products which act specifically on a subset of primary afferent sensory neurons to open a novel cation-selective ion channel in the plasma membrane. These sensory neurons are involved in nociception, and so, these agents are targets for the design of a novel class of analgesics. Although synthetic agonists at the capsaicin receptor have been described previously, competitive antagonists at this receptor would be interesting and novel pharmacological agents. Structure-activity relationships for capsaicin agonists have previously been rationalized, by ourselves and others, by dividing the capsaicin molecule into three regions--the A (aromatic ring)-, B (amide bond)-, and C (hydrophobic side chain)-regions. In this study, the effects on biological activity of conformational constraint of the A-region with respect to the B-region are discussed. Conformational constraint was achieved by the introduction of saturated ring systems of different sizes. The resulting compounds provided agonists of comparable potency to unconstrained analogues as well as a moderately potent antagonist, capsazepine. This compound is the first competitive antagonist of capsaicin and resiniferatoxin to be described and is active in various systems, in vitro and in vivo. It has recently attracted considerable interest as a tool for dissecting the mechanisms by which capsaicin analogues evoke their effects. NMR spectroscopy and X-ray crystallography experiments, as well as molecular modeling techniques, were used to study the conformational behavior of a representative constrained agonist and antagonist. The conformation of the saturated ring contraint in the two cases was found to differ markedly, dramatically affecting the relative disposition of the A-ring and B-region pharmacophores. In agonist structures, the A- and B-regions were virtually coplanar in contrast to those in the antagonist, in which they were approximately orthogonal. A rationale for agonist and antagonist activity at the capsaicin receptor is proposed, based on the consideration of these conformational differences.

Muscarinic activity of the thiolactone, lactam, lactol, and thiolactol analogues of pilocarpine and a hypothetical model for the binding of agonists to the m1 receptor.

Pilocarpine isosteres have been synthesized and characterized with regard to their in vitro muscarinic properties. The results indicate that the carbonyl oxygen of the lactone function of pilocarpine is of primary importance for agonist activity with the ether oxygen being of lesser or secondary importance. An X-ray structure determination for the hydrogen O,O'-ditoluoyltartrate salt of thiolactone pilocarpine isostere 2a has been performed. This compound has an unusual pharmacological profile exhibiting M1-agonist selectivity as well ass presynaptic antagonism. As a result this compound is also viewed as having therapeutic potential for Alzheimer's disease. A model for the binding of pilocarpine and other muscarinic agonists to the third transmembrane helix of the human m1 muscarinic receptor has been developed.

Overcoming multidrug resistance in Chinese hamster ovary cells in vitro by cyclosporin A (Sandimmune) and non-immunosuppressive derivatives.

Cyclosporin A (Sandimmune) increased the in vitro susceptibility of 'parental' and 'multidrug-resistant' (MDR) chinese hamster ovary (CHO) cell lines to three anti-tumour drugs: colchicine, daunomycin, and vincristine. Several immunosuppressive or non-immunosuppressive derivatives of cyclosporin (Cs) were compared for their ability to sensitise both parental and MDR cells to chemotherapeutic agents. Although 5-10-fold increases of sensitivity to anti-tumour drugs could be obtained for cells of the parental line with several Cs-derivatives, the largest 'gains' of sensitivity (chemosensitisation) were obtained for the cells of the MDR line and with only some of the Cs derivatives. The MDR cells employed displayed the typical MDR phenotype. However, we found no correlation between the immunosuppressive activity of Cs derivatives and their capacity to reverse MDR and all four possible combinations of these two activities could indeed be shown among the tested Cs derivatives. This study demonstrates for the first time that some immunosuppressive Cs can be devoid of chemosensitising activity.

2-Epimutalomycin and 28-epimutalomycin, two new polyether antibiotics from Streptomyces mutabilis. Derivatization of mutalomycin and the structure elucidation of two minor metabolites.

A number of derivatives of mutalomycin (1), a naturally occurring polyether antibiotic, have been synthesized. In the desulfurization reaction of the ethylthio derivative (5) of mutalomycin (1) with Raney-nickel we observed an unusual course of the reaction, namely the introduction of a hydroxy group instead of the usual exchange against hydrogen, leading to two reaction products, mutalomycin (1) and 28-epimutalomycin (3). The structure of 3 and 2-epimutalomycin (2), both minor metabolites from the mutalomycin fermentation, were elucidated by X-ray analysis.

Characterization of dopamine receptor subtypes by comparative structure-activity relationships: dopaminomimetic activities and solid state conformation of monohydroxy-1,2,3,4,4a,5,10,10a-octahydrobenz[g]quinolines and its implications for a rotamer-based dopamine receptor model.

A series of phenolic (cis)- and (trans)-1,2,3,4,4a,5,10,10a-octahydrobenz[g]quinolines were investigated in the D1 and D2 dopamine (DA) models, DA-sensitive adenylate cyclase and electrically evoked acetylcholine release, respectively, and were compared with the effects of the corresponding aminotetralins. A similar structure-activity pattern was found at both DA receptor subtypes. The change from the bicyclic to the tricyclic DA analogs resulted in a loss of activity of all beta-rotameric 8-hydroxy derivatives, suggesting the presence of a steric barrier. Derivatives of the alpha-rotameric 6-hydroxy trans series, in contrast to their inactive cis analogs, showed stimulatory effects that increased from N-methyl to N-n-propyl substitution, indicating an interaction with an N-alkyl binding site. The inactivity of the corresponding N-n-butyl derivative ("N-butyl phenomenon") suggests that the N-alkyl substituents of this series point toward a "small N-alkyl binding site," which can be differentiated from a "large N-alkyl binding site." An X-ray of the active (-)-enantiomer of (trans)-6-hydroxy-N-n-propyloctahydrobenz[g]quinoline-(R)-mandelat e revealed a 4aR, 10aR absolute configuration, corresponding to that of (-)-5-hydroxy-2-(N,N-di-n-propylamino)tetralin. The hydrogen bonding interactions of the axial N+-H proton and the hydroxy group to mandelate anions in the crystal provide a model for a possible drug-receptor interaction. Molecular modeling served to localize the steric barrier and the boundaries of the small N-alkyl binding site, which together form an "extended steric barrier." The results led to the proposal of a refined version of a rotamer-based general DA receptor model, which is supplemented by criteria for the orientation of DA agonists. Its application is demonstrated with apomorphine and ergoline.