Synthesis of Silicon and Germanium Containing Heteroaromatic Sulfides as Cholesterol Level Lowering and Vasodilating Agents

Silicon and germanium containing heteroaromatic sulfides have been prepared using phase transfer catalytic (PTC) system thiol / Si or Ge containing alkyl halide / solid KOH / 18- crown-6 / toluene. The target sulfides were isolated in yields up to 92 %. It has been found that 2-{[dimethyl (β-triethylgermylethyl)-silylmethyl]thio}-1-methylimidazole and 2-{[dimethyl(β-triphenylsilylethyl) silyl-methyl]thio}benzothiazole are the most active cholesterol level lowering and vasodilating agents.


INTRODUCTION
Coronary heart desease (CHD) remains the leading cause of death in the industrialized countries. The primary cause of CHD is athemsclemsis, a disease characterized by the deposition of lipids in the artedal vessel wall, resulting in a narrowing of the vessel passages and ultimately hardening the vascular system. Atherosclerosis as manifested in its major clinical complication, ischaemic heart disease, is thought to begin with local injury to the arterial endothelium followed by proliferation of artedal smooth muscle cells from the medial layer to the intJmal layer along with deposition of lipid and accumulation of foam cells in the lesion. As the athemsclerotic plaque develops, it progressively occludes more and more blood vessel and can eventually lead to ischaemia or infarction. Therefore, it is desirable to provide a method of inhibiting the progression of atherosclemsis in patients.
Elevated cholesterol levels are also associated with a number of disease states. Therefore it is desirable to provide a method for reducing plasma cholesterol in patients with, or at risk of developing restenosis, angina, cerebral arteriosclerosis, and xanthoma.
The silicon and germanium containing heteroammatic sulfides as cholesterol level lowering and vasodilating agents have not been studied. In this view the silyl and germyl S-substituted derivatives of Nand S-heterocyclic thiols are of interest as substances with the possible above described activity.
The preparation of the compounds possessing serum cholesterol level lowering property [41] is the aim of our work.
We have used the first [45] of these methods for the preparation of Si and Ge derivatives of N-methylimidazole, pyridine, quinoline, benzothiazole, and purine sulfides to test their serum cholesterol lowering and vasodilating activities.

Synthesis of Silion and Germanium Containing Heteroaromatic
Sulfides as Cholesterol Level Lowering and l/'ascodilating Agents MATERIAL8 AND METHODS CHEMISTRY H NMR spectra were recorded on a Varian 200 Mercury instrument using CDCI as solvent and hexamethyldisiloxane (HMDSO) as internal standard. Mass spectra were registered on a GC-MS HP 6890 (70 eV). GC analysis was performed on a Chrom-5 instrument equipped with flame-ionization detector using glass column packed with 5 % OV-101 / Chromosorb W-HP (80-100 mesh) (1.2 m x 3 mm). Bromomethyltdmethylsilane and 3-iodopropyltrimethylsilane were obtained by Gdgnard reaction [47,48] Finely powdered dry K2COz was added to a solution of 10 mmol of thiol (3-9), 10 mmol of corresponding silyl or gerrnyl substituted alkyl halogenide and 18-crown-6 (lmmol, 264 mg) in 25 ml of toluene. The mixture was refluxed with stirring to achieve the disappearance of the substrates, filtered over the thin silica gel layer and concentrated under reduced pressure. The residue was purified by column chromatography using the mixture benzene-ethyl acetate as eluent. PHARMACOLOGY CHOLESTEROL LEVEL LOWERING ACTIVITYASSAY Five months old male ICR mice were housed in an air-conditioned room (23 C and 60% humidity) under an artificial 12-hr light-dark cycle (7:00 am-7:00 pm). Animals were maintained on a basal diet or a high-cholesterol diet supplemented with linoleic acid. The basal diet contained 20% casein, 63.2% sucrose, 10% coconut oil (linoleic acid content: below 1%), 2 % agar, 0.8% vitamin mixture, and 4% salt mixture. The high cholesterol diet consisted of the basal diet plus 1.5% cholesterol and 10% linoleic acid, but the corresponding 2% of sucrose were omitted from the basal diet. We divided 50 mice into 2 groups and gave different diets as follows: for 10 mice the basal diet (control group), and for 40 the high cholesterol diet (HC group). Each animal received 5 g of the respective diet daily for 12 weeks. Water was freely available.
9 Weeks after start of the experiment the total and HDH cholesterol were determined in the serum of intact control and high-cholesterol diet animals (3 from each group). High-cholesterol diet group was divided into Cholesterol control group (7 mice) and 5 groups (6 mice each) treated with the studied compounds (10 rng/kg i.p. once a day for 3 weeks).
At the end of the experiment (12 weeks), the mice after overnight fasting were killed by withdrawing blood from the abdominal aorta under ether anaestesia. Serum was separated by centrifugation (1500 g for min), and high-density lipoprotein (HDL) fraction was immediately separated from a portion of the serum by the heparin-manganese precipitation procedure.
Total and HDL cholesterol in the serum and aorta were determined flumenzymatically.
The results obtained were expressed as the mean + SEM of data from 5-7 mice per group.

VASODILA TING ACTIVITYASSA Y
The modified classical method for the experiments on the isolated perfused rabbit ear blood vessels was used. Rabbits of both sexes (2.6-3.3 kg) were killed by i.v. injection of pentobarbital sodium (80 rng/kg). The central ear artery was dissected free at the base of the ear and cannulated with polyethylene tubing and perfused at a constant flow (2ml/min) from 4-channel peristaltic pump Gemini (Italy).
The content of the perfusion fluid (mmol) was as follows: NaCI 136.9; KCI 2.68; CaCI2 1.8; MgCI2 1.05; NaHCO3 11.9; NaH2PO4 0.42; glucose 5.6 (pH 7.35 at 22C). Intraluminal inflow perfusion pressure was measured with a Statham P23J transducer and recorded on the physiograph DMP-4B (Narco Bio-Systems, USA). As flow remained constant, the changes in perfusion pressure reflected changes in blood resistance, i.e. the degree of vasoconstriction or relaxation. Vasoconstriction was caused by intraluminal infusion of noradrenaline (10 /mol). The investigated compounds were dissolved in the perfusion fluid. The relaxant responses to the investigated compounds used in the different concentrations (10 and 50 /mol) were tested. Responses are expressed as per cent relaxation (% changes in the perfusion pressure) without and with the investigated compounds.

ACUTE TOXICITYASSAY
The acute toxicity was evaluated in male ICR-JCL mice (19-23 g). The compounds were dissolved-suspended in 0.6% solution of Twin 80 and injected i.p. To reduce the number of the used animals and the amount of compounds the maximal dose (400-600 mg/kg, i.p.) was used. If possible LDs0 was calculated when 50% of the animals died. 86 Metal BasedDrugs VoL & Nr. 2,2001 RESULTS AND DISCUSSION CHEMISTRY Hydrosilylation and hydrogermylation of the chloromethylvinyldimethyisilane with diethylmethylsilane, triethylsilane, triphenylsilane, and triethylgermane have been used to obtain silyl(germyl)containing alkylchlorides lad. Trialkyl(aryl)silane or germane was added to vinylsilane in the presence Speier's catalyst (0.1 M solution H2PtCI.6H20 in absolute isopropyl alcohol). The reactions were exothermic and gave 1,3-disilyl(germyl)substituted ethanes in good yields (up to 98 %) ( Table 1).
It was necessary to transform the silyl(germyl)containing alkylchlorides l a d into iodides due to the low reactivity of alkylchlorides under phase transfer catalysis conditions. The chlorine atom exchange for iodine was performed with Nal in acetone by usual procedure giving the corresponding alkyliodides 2ad (in yields up to 74 %) ( A simple method for the preparation of silyl and germyl derivatives of the Nand Sheterocyclic thiols was developed. The phase transfer catalytical system solid K2CO/18-crown-6/toluene was used. Application of the stronger base (KOH) led to the destruction of alkylating agents. Despite to the mild reaction conditions triphenyisilyl derivative 2c partly decomposed. Therefore the yield of 2-{[dimethyl(l-triphenylsilylethyl)silylmethyl]thio}benzothiazole Sd was 13%.
The aimed substances were obtained with good chemical yields (up to 92%) in a short time under mild conditions ( 3 (a-e)-9 (a-e) The purity of the synthesized compounds was detected with HPLC (<1.5% of impurities). All substances were mobile oils therefore the elemental analysis was performed only for 8a and 9a.
The structures and spectral characteristics of synthesized substances are shown in Tables 3   and 4.     and 1'.84 (both s, 9H, ' Table 5  The cholesterol level lowering activity depends also on the substituent position in the ring: the 2-position in the pyddine and quinoline is more preferable. Thus 2-[(y-tdmethylsilylpropyl)thio] derivatives of pyridine 4a and quinoline 6a are more active than the similar derivatives of 4-pyddine 5a and 8-quinoline 7a.
We have found that imidazole derivatives 3a, b, e exhibit high vasodilating activity in experiments in vivo. The most active was 2-{[dimethyl(l-triethylgermylethyl)silylmethyl]thio}-l-90 methylimidazole (3e). The exchange of imldazole ring to benzothlazole, quinoline or purlne decreases the vasodilating activity. Unexpectedly, the replacement of triethylsilyl group in the compound 8c by triphenyl group (8d) changes the action type from strong vasodilation to medium vasoconstriction.

ACUTE TOXICITY
The acute toxicity of the substances 3a, b, e; Sa and 8a, b, c, d, e, that were investigated as the cholesterol level Iowedng and vasodilator agents, was also determined ('l'able 7). The studied compounds have a medium toxicity. The most toxic was silyl substituted imidazole sulfide 3b (200 mg/kg). The replacement of silicon atom by germanium one (3e) leads to the decrease of acute toxicity (435 mg/kg). In general, silyl and germyl substituted benzothiazoles (Sb e) are less toxic than the corresponding imidazole analogues (3b, lh).

CONCLUSIONS
The PTC method of the synthesis of hetemcyclic silyl-and germylalkylsulfides was elaborated. Thirteen compounds were synthesized and isolated in the yield up to 92%. ! Edmunds Lukevics et al.
Synthesis of Silion and Germanium Containing Heteroaromatic Sulfides as Cholesterol Level Lowering and Vascodilating Agents They were studied as serum cholesterol level lowering agents. It has been found that silicon and germanium containing heteroaromatic sulfides possess the cholesterol level lowering activity. The 1-methylimidazole, benzothiazole and 2-quinoline derivatives 3e, 6a, 8a, b, e exhibit the highest level of activity. The substances containing dimethyl(l-triethylgermylethyl)silylmethyl-(3e) and dimethyl(l-triphenylsilylethyl)silylmethyl-(8d) substituents were the most active.
Ten of the elaborated compounds were tested on the vasodilating activity. It was shown that 1-methylimidazole derivatives 3a, 3e possess the vasodilating activity. The compounds containing benzothiazole have the different influence. Compound with dimethyl(l-triethylsilylethyl)silylmethyl-substituent (8c) has the relaxation effect. On contrary the 3trimethylsilylpropyl-(8a) and dimethyl(l-triphenylsilylethyl)silylmethyl (8d) benzothiazole derivatives possess the contraction effect.
The toxicity of the studied substances was low. It was shown that germanium derivative 3e was less toxic than its silicon analogue 3b. The introduction of the second silicon or germanium atom also decreases acute toxicity of the compound (Sa and 8b, c, d, e).