Structure-activity relations imidazolines

The only aspect of octopaminergic transmission for which a relatively large amount of structure-activity data is available relates to the properties of OA-receptors themselves. Agonists that stimulate these systems and antagonists that block them, are known and such compounds exist in several structural groups. The three major groups of agonists currently identified are phenylethylamines amidines and imidazolines. 

Tolazoline and the structurally related imidazoline tetrahydrozoline may be H2 receptor agonists since tolazoline-induced acid stimulation in the dog can be blocked by burimamide, metiamide and cimetidine and both imidazolines induce characteristic -agonist effects on isolated guinea pig atria preparations which can be blocked by metiamideJ Clonidine, like the imidazolines, has a-adrenergic agonist activity... 

Timmermans, P. B. M. W. M., Hoefke, W., Stahle, H., van Zwieten, P. A., Structure activity relationships in clonidine-like imidazolines and related compounds, Progr. Pharmacol. 3 1-104,1980. 

In a few cases the formulae given above are oversimplified, in the sense that commercial materials contain other related compounds which may complicate their analysis. The complexity of a-olefin sulphonates has already been mentioned. With such mixtures, conversion of a titration volume to an active percentage is not straightforward, because it is debatable which constituents should be considered as actives, and the effective molecular weight is uncertain. A more complicated case is that of imidazoline and imidazolinium derivatives. The chemistry involved in the synthesis of these materials is very complex, and it seems likely that all the commercial materials contain a mixture of several different active structures [1,2]. 

Arens, M., R. Spilker, Fatty acid amidopropylbetaines—determination of fatty acid amidopro-pylamine—collaboration of the DGF. Communication 150 German standard methods for study of fats, fatty products, surfactants and related materials. Communication 116 Analysis of surface active materials XXV (in German), Fett Wiss. TechnoL, 1995, 97,468-470. Schwarz, G., P. Leenders, U. Ploog, Condensation products of fatty acids or their methyl esters with aminoethylethanolamine (in German), Fette, Seifen, Anstrichm., 1979,81, 154-158. Takano, S., K. Tsuji, Structural analysis of the amphoteric surfactants obtained by the reaction of l-(2-hydroxyethyl)-2-alkyl-2-imidazoline with ethyl acrylate,/. Am. Oil Chem. Soc., 1983, 60,1798-1806. 

The commercially available complex 2 shows higher activity and is metathesis active under mild conditions, typically ambient temperature up to 90 °C [3c, hj. RCAM reactions with 2 are often run at 80 °C in toluene or a related aromatic solvent However, rigorously inert (anhydrous and oxygen-free) conditions are required. The core structure is amenable to tuning by ligand modifications, reflected in a recent report which demonstrated that the effective RCAM of diyne 6 can be performed at room temperature to afford cyclic alkyne 8 in excellent yield when imidazolin-2-iminato tungsten alkylidyne catalyst 7 was employed (Scheme 7.5) [12], The same catalyst has also been employed in the preparation of cyclophanes [13]. 

---