Six- and Seven-Membered 1-Oxa-4-Aza-2-Silacyclanes as Possible Correctors of Adaptational Mechanisms

The biological activity of eight 1-oxa-4-aza-2-silacyclanes with the OSiCH2N fragment including 6-membered 2-sila-5-morpholinones (1–3) and 4-acyl-2-silamorpholines (4–6)and previously unknown 7-membered derivatives of salicylic acid (7, 8) was studied. Compounds 1 and 3–6 show the certain antihypoxic action. Compounds 2 (40 mg/kg), 4 (20 mg/kg), 6 (40 mg/kg), 7 (20 mg/kg) and 8 (40 mg/kg) reduce the physical serviceability of intact animals. Compound 1 (20 mg/kg) influences the physical serviceability in a moderate-positive way on the background of chlorophos-poisoning. Compounds 5–8 displayed protective properties against chlorophos-poisoning at the LD50 dose and compounds 2, 4, 5, 7 at the LD100 dose. Influence of compounds 1 and 2 on the emotional-research behavior of mice was studied.


INTRODUCTION
At present the pentacoordinated organosilicon compounds are the objects of intense investigation because of their unique structures, possible role as the intermediates in S-Si reactions and biological activity [1][2][3]. The increased reactivity of such compounds revealed in the course of last years led to investigation of their synthetic applications [2]. In particular, these compounds may be used as precursors for the organoheterosilacyclanes, for example, 1-oxa-4-aza-2-silacyclanes [4,5]. Taking into account the known physiological significance of silicon and biological activity of organosilicon derivatives (synthesis of glycosaminoglycanes, influence on the calcium, magnesium and aluminium exchange and oxidation metabolism, combination of psychotropic and vazoactive properties and membrane-stabilizing action [3]), it was reasonable to investigate these compounds as the potential correctors of the adaptational mechanisms.

MATERIALS AND METHODS
The IR specra of the compounds were recorded in thin layer and solutions in KBr cells on a Specord IR-75 instrument. The H NMR spectra of solutions in CDCI3 were recorded on a Varian XL-400 spectrometer at 400.0 MHz. The chemical shifts were measured using TMS as internal reference.
For preliminary data on the biological activity of compounds 1 and 2 see [6]. Synthesis of 7-membered silacyclane 7 was carried out in comparison with Scheme 1 using N-methylsalicylamide as initial compound. The amide was transfomed into monosilylated product 9 and then into bissilyl derivative 10 using common mutes. Reaction of the latter with chloro(chloromethyl)dimethylsilane (CCMDMS) led to desired silacyclane 7o  (9). HMDS (188 ml, 0.9 mol) was added dropwise to 45 g (0.3 mol) of the N-methylamide of salicylic acid. The reaction mixture was refluxed under vigorous stirring for 2 h. After removing the excess of HMDS in vacuo the residue was fractionated and 58 g (95%) of the desired product (9) were obtained. B.p. 160-161C (10 mm Hg), nD 1 (10). Trimethylchlomsilane (TMCS, 36.7 g, 0.34 tool) was added dropwise to a solution of 47 g (0.23 mol) of compound 9 and 52 ml (0.34 mol) of triethylamine in 100 ml of diethyl ether. The reaction mixture was refluxed under vigorous stirring for 3 h. The precipitated salt was filtered out, the solvent was removed in vacuo. After the fractionation of the residue 50 g (78%) of compound 10 were obtained. B. p. 143-144C (10 mm c. One-pot synthesis of silacyc/ane (7). The mixture of 10 g (36 mmol) of amide 10 and 3 g (36 mmol) of CCMDMS was heated until the complete elimination of TMCS (64-66C, 9.2 ml, 100%). After the fractionation of the residue 6.9 g (86%) of silacyclane 7 were obtained. B. p. 178 (11) and (O--SO-chelated O-trimethylsilyI-N-(dimethylchlorosilylmethyl)-N-methylsa/icy/amide (12). CCMDMS (1.6 g, 11 mmol) was added dropwise to the solution of 2.25 (10 mmol) of amide 10 in 5 ml of diethyl ether. In 5 min the presence of an intense band of of Adaptational Mechanisms O-silylmethylated product (1669 cm-) along with the bands at 1636 and 1597 cmcorresponding to the compound 10 and the N-silylmethylated product 12, respectively, was detected in the IR spectrum of the reaction mixture. Afterwards the quick decrease of the bands at 1669 and 1639 cmalong with a moderate increase of the band at 1597 cmwas observed. In 30 min only the product of N-silylmethylation 12 was detected in the IR spectrum of the mixture. After the removal of TMCS and ether in vacuo at room termperature 2.6 (79%) of the chloride 12 were obtained (yellow oil). IR spectrum (v, cm)" 1597, 1500 (NCO). 'H NMR spectrum (

Biological study
The experiments were carried out on white alley mice, hams, weight 16-24 g. All compounds were injected as water emulsion in 'twin-80' intraperitoneal in the given range of doses before an hour to the beginning of the registration of parameters. The animals of control groups were injected with adequate volumes of salt infusion. The quantity of animals in each group varied from 6 to 15. For data processing the basic methods of parametrical and unparametrical statistics (t-criterion Student, discriminant function analysis, cluster analysis, correlation analyses) were used. Acute toxicity of compounds was defined by the express train-method of V. Prozomvsky [7]. Acute hypobaric hypoxia (AHBH) was simulated in the flowing hypobaric chamber (absorber of carbon dioxide, the 30% solution of KOH at 18-22C) by 'raising' of the animals on the height of 11000 m with the average speed of 50 m/sec. The survival rate of animals and the time of their death (reserve time) were estimated [8].
Acute immersion cooling (AIC) was simulated by compulsory navigation without loading in ice water (3.5-4.0 C). The duration of life of the animals had been estimated until the clonic spasms and characteristic 'pose of capuchin' appeared.
Physical serviceability (PS) was estimated on duration of floating in water at 28-29 C with a cargo. It was attached to the basis of a tail, equal to 5% from weight of a body [9].
The preventive maintenance of acute organophosphorus compounds poisoning (OPhC). The compounds were injected an hour before the chlorophos poisoning (1% solution, subcutaneosly in doses LDo and LDoo). The survival rate had being analyzed within a day.
Therapeutic effect of the compounds at an acute organophosphorus compounds poisoning (OPhC). The compounds were injected an hour before the chlorophos poisoning (1% solution; subcutaneosly in doses LDso and LDoo). The survival rate had being analyzed within a day.
The influence of compounds on individual behavior. The psychotmpic effects of the compounds on individual rough-research behavior were studied on the model called 'an open field'. The 'open field' for mice was composed of a chamber by the size 40x40x40 sm, painted in white Andrey V. Kurocha, Olga V. Agafnova et al.
Metal-Based Drugs colour and closed by a transparent cover. The floor of the chamber was lined on squares 10x10 sm with a round aperture ('mousehole') with a diameter of 3 sm at the centre of each square. The research was carried out at electrical illumination by a glow-lamp with capacity 100 W, located on distance 1.5 rn from the center of the field.
Behavior of each animal was estimated individually. A mouse was placed in the left corner of the chamber. The complete structure of behavior had being registered for 4 minutes. It included the following elements: smelling, moving, movement on a place, condition in a rule sitting, looking in 'mousehole', vertical rule (stance with an emphasis, vertical stance), grooming, freezing, and also the number of defecations and micturitions. It is necessary to add that not only the expression of elements of behavior was estimated but also the probabilities of transitions from one condition into the other were estimated [13].
The influence of compounds on metabolism was described by us previously [6].

RESULTS AND DISCUSSION Chemical Aspects
The general synthetic approach to 1-oxa-4-aza-2-silacyclanes consists of the next steps. The initial compounds are the monosubstituted amides of carboxylic acids containing the additional hydroxylic group at the acid radical or/and at the substituent at the N atom. On the first stage (Schemes 1,2, reactions a) this group should be protected by the transformation into the corresponding O-trimethylsilyl derivative. One of possible ways for the next stage is the reaction of the latter with CCMDMS in the presence of a base (amination method) leading to the unstable (OSi)-chelated products of N-chlorodimethylsilylmethylation which contain the pentacoordinated silicon atom. The thermal decomposition of these compounds with the elimination of MezSiCI in the course of fractionation gives the desired silacyclanes. By this method, the known 2-sila-5morpholinones 1-3, 4-acyl-2-silamorpholines 4-6 and the derivative of salicylic acid 8 (Scheme 2) were prepared.
The higher yields of desired silacyclanes 1-6 and 8 may be obtained without the isolation of unstable pentacoordinated organosilicon chlorides. The existence of such intermediate compounds was detected by the IR and NMR monitoring [5]. IR specra of impure chlorides show two bands at 1600-1605 and 1515-1520 cmof chelate C()NCH2;i fragment [10]. Intramolecular interaction O-Si in these compounds was also confirmed by the upfield shift of signals in the Si NMR spectra (up to-30 /-40 ppm), which testifies to the presence of pentacoordinated silicon atom [, ]. Another way includes the transformation of the O-silylated product 9 under rather drastic conditions into the corresponding bis-O,N-trimethylsilylmethylated product 10 (Scheme 1, reaction b) following by the reaction with CCMDMS (reaction c, transsi/y/ation method).
The formation of intermediate O-silylmethylated product 11 and its subsequent isomerization into the N-silylmethylated product 1:2 (reactions c, d) were confirmed by the IR specmscopy.
The general scheme of the reactions of trimethylsilyl derivatives of amides and lactams with CCMDMS includes the intermediate product of transsilylation [12]. However, in the case of bis-O,N-trimethylsilyl derivative 10 the corresponding product of could not be detected by the IR spectroscopy and so it was excluded from scheme 1.

Pharmacology
The definition of acute toxicity of silacyclanes 1-8 on the first investigation phase revealed their low toxicity (LDo 400-500 mg/kg) [14] and allowed to choose the acceptable doses for the following experiments. Futher the doses equal 1140-1110 LDo (10,20, 40 mg/kg) were used.
The study of antihypoxic activity of silacyclanes 1-8 (Table I)  Metal-Based Drugs of life. The analysis of experimental results allows to assume the presence of certain antihypoxic activity of compounds 1, 3-6. The observed antihypoxic effects are comparable with the effects of (2-oxo-l-pyrrolidinyl)acetamide (nootropil) or sodium 7-hydroxybutanoate in effective doses [8].
Compounds 7 and 8 showed no antihypoxic activity.
The effects of compounds 1 and 2 were investigated using the model of acute immersion cooling. They showed no influence on resistance of mice to AIC (see Table I).
It is known that the adaptation of organism to AHBH and OPhC compound poisoning has common mechanism [15]. Therefore, the combination in system screening of models AIC and OPhC poisoning was of interest as a confirmation of direct correlation between frigoprotective properties of compounds and their influence on PS. Besides, it was necessary to expect the return dependence between antihypoxic activity and stimulating action (on the AHBH and OPhC model), and also the OPhC-protective action and stimulating action.
It was found that 2-sila-5-morpholinones 1 and 2 do not render the expressed negative action on the spectrum of individual behavior.  Fig. 1. Graph-structure of the mice behavior in "open field" in an hour after the introduction of compounds 1 and 2. Circles are the behavioral patterns (the diameter corresponds to the degree of expression), arrows show the probability of transitions of behavior elements (the thickness corresponds to statistical meanings of the probability).