N-(3,4-Dichlorobenz~I)azoles - Investigations Regarding Synthesis, NMR-Spectroscopy and Affinity Towards Sisma-I and Sigma-2 Receptors

A series of azoles and aminoazoles with a 3,4-dichlorobenzyl moiety attached to a ring nitrogen atom was synthesized via reaction of the parent systems with 3,4-dichlorobenzyl chloride. Regioisomeric products were discriminated on the basis of ' 3 data or by NOE-difference spectroscopy. The affinities of some representatives towards sigma-1 and sigma-2 receptors were determined by receptor binding assays. (mlz, (M', 159 (100). (228.08): C, 47.40; H, 3.09; N, 18.42. Found: C, 47.69; H, 3.10; N, 18.44.


Introduction
Since their discovery in 1976 sigma receptorsinitially proposed as a subtype of opioid receptorand their physiological role have been investigated extensively; several reviews provide condensed information in this regard [I-61. Two subclasses of sigma receptors have been identified, designated as sigma-I and sigma-2 receptors [3]. Sigma receptors are distributed in the central nervous system but also in many peripheral tissues such as in liver and kidney and, moreover, are highly expressed in various tumor cells [3]. They respresent high affinity binding sites for many psychotropically active compounds and thus sigma receptor ligands are anticipated to play a potential role as antipsychotics and antidepressants.
A considerably large variety of structurally unrelated compounds were found to be able to bind to sigma receptors. Amongst these structures 3,4-dichlorophenethyl substituted ethylenediamines of type A (Figure 1) deserve special interest as they were found to exhibit high affinities andadditionallyto be selective for sigma receptors over other systems [7]. In the course of a program dedicated to the development of more potent and, particularly more selective sigma receptor ligands we synthesized a variety of compounds related to structure A [8]. Thus, for instance, leaving the left part of the molecule unchanged, the saturated N-heterocyclic system in A was replaced by other heterocyclic and also heteroaromatic moieties or even by longer carbon chains. Moreover, the length of the central aliphatic part in A was systematically varied. Some of the thus obtained compoundse.g. the pyridine derivative Bnot only showed high affinities but also interesting sigma-llsigma-2 selectivities ( Figure   1) [8]. Within these investigations also the minimal requirements for sigma receptor affinity of more or less related compounds became a matter of interest. In this regard, we here report on the synthesis of various 3,4-dichlorobenzylazoles (Scheme 1) and their affinity towards sigma-I and sigma-2 receptors. The envisaged structures result from a drastic reduction of the structural elements in molecules of type A or B, only leaving (a) slightly basic azole nitrogen atom@) as well as the lipophilic 3,4-dichlorophenyl moiety.

Chemistry
Compounds 1-14 were prepared in single step reactions upon prolonged refluxing of the sodium salt of the appropriate parent azole with 3,4-dichlorobenzyl chloride in dry ethanol. Except with pyrazole and imidazole, the formation of regioisomeric alkylation products is possible and this was observed in most cases as well. The separation of the thus obtained isomeric mixtures was achieved by column chromatography. Accordingly, compounds 1-5 could be prepared in satisfying yields. In contrast, the isomeric mixtures resulting from alkylation of compounds carrying an amino substituent at the azole core were difficult to purify.
In these cases clean separation of the regioisomers by column chromatography was not always possible or resulted in low yields of the pure compounds (mixed fractions predominating). Upon reaction of 3-tert-butyl-pyrazol-5-amine with 3,4dichlorobenzyl chloride also alkylation at the exocyclic amino function was observed (formation of compound 14).

NMR Spectroscopic Investigations
The NMR data of all investigated compounds are given in Tables 1-3.
According to refs. [9-121 unequivocal discrimination between regioisomeric structures was achieved by application of NOE-difference spectroscopy and considering ' 3~1 '~ coupling information. Thus, for instance, the l-substituted tetrazole 5a can be easily distinguished from its 2-substituted congener 5b via an NOE on the azole-H signal upon irradiation of the NCH2 transition ( Figure 2).

N-(3,4-Dichlorobenzy/)azoles, General Procedure
To a solution of sodium ethylate prepared from sodium (345 mg, 15 mmol) in dry ethanol (23 mL) was added the azole (15 mmol) and the mixture was stirred for 30 min. Then 3,4-dichlorobenzyl chloride (2.932 g, 15 mmol) was added and the mixture was heated to reflux for 12-36 h. After filtration of the sodium chloride formed during the reaction the solvent was removed under reduced pressure and the residue was purified as given below.