Synthesis and Antibacterial Evaluation of Some New Fused Cyclic Sulfoxides

ABSTRACT A series of diarylidine cyclohexanones (1t-12t) have been prepared via ClasienSchmidt reaction then condensed with dimethyl sulphoxide through Michael-Claisen condensation to afford the corresponding fused heterocycles (13t-24t). The structures of the products were elucidated by the spectrum (UV, IR, H-NMR). The suggested mechanisms for these reactions were investigated according to theoretical calculations, heat of formation (H.F.) and the steric energy (S.E.). Furthermore some of the products have been tested for their biological activity (antibacterial).


INTODUCTION
Sulfoxides are compounds that contain a sulfinyl group covalently bonded at the sulfur atom to two carbon atoms and oxygen atom (Segurel et al., 2005).The naturally occurring sulfoxides are often accompained by the corresponding sulfides or sulfones (Lake et al., 1988).The most commercially important sulfoxide is the simplest member, dimethyl sulfoxide.Sulfoxides occur widely in small concentrations in plant and animal tissues (Wiley and Sons, 2001).Sulfoxides have fascinated organic chemists for a long time owning to their varied reactivity as a functional group for transformation into a variety of organo sulfur compounds.These transformations are ureful for the synthesis of drugs and sulfur -substituted natural products (Musah et al., 2009).Optically active sulfoxides continue to deserve much attention as important chiral auxiliaries in asymmetric synthesis and in C-C bond forming reactions (Abbas et al., 2005).A novel bioactive sulfoxide like Nacetyl-2-(1-adamantylsulfoxo)-3-acetoxy-4-phenyl-6-hydroxy-1,2,3,6-tetrahydropyridine was tested for anti-microbial action using the agar dilution method against twenty one microorganisms gram -positive and gram -negative bacteria and diploid fungus.It was found that the sulfoxide inhibited the growth of Moraxella catarrhalis and Streptococcus pyogenes with minimum inhibitory concentration.inaddition, the growth of Corynebacterium diphtheriae (NCTC) was partially inhibitted (80%) at 256 µg/ml (Prachayasittikul et al., 2010).
Different routes were used to afford the cyclic sulfoxides such as the condensation of MeS(O) CH 2 -Na with phCH=CHBz in liquid ammonia which gave 3-hydroxy-3,5-diphenyl -1-thiacyclohexane-1-oxide as shown below (Gautier et al., 1970).Chloroperoxidase was used as catalyst in the synthesis of a series of aromatic cyclic sulfoxides.This have been acheived by the reaction as shown below (Allenmark and Andersson, 1996).
Michael addition of DMSO to permethylated core of oligosaccharides was used in the formation of covalent DMSO products adducts as shown below (Sioud et al., 2010).

Materials
All chemicals was supplied from Fluka, Sigma and Aldrich company.Melting points were determined by Electrothermal 1A 9000 Digital -series 1998 apparatus (uncorrected).
UV-visible spectra were recorded using Shimadzu UV-Vissible spectrophotometer 160 (Department of Chemistry -College of Science -University of Mosul).
Fourier-Transform Infrared spectra were recorded on Brucker Tensor spectrophotometer 2003 (Germany) (Department of Chemistry -College of Science -University of Mosul).
Nuclear magnetic resonance ( 1 H-NMR) spectra were recorded using, 500 MHz perkin Elmer spectrometer, using tetramethylsilane (TMS) as an internal standard, CDCl 3 as a solvent was used in our investigation.(Department of Chemistry-I.I. T. Roorkee , India).
The theoretical calculations based on the data obtained from the minimized geometry were computed using semi-empirical AM1 module in the CS Chem.Office 2003 version 8.0 molecular modeling package.
These compounds were prepared by stirring (3.7mmol) of the cyclohexanone with 7.5 mmol of the desired benzaldehyde, and 5 ml of 10% ethanolic sodium hydroxide in 25 ml ethanol in a 50 ml round-bottomed flask.After 3 hours the reaction mixture was filtered to obtain the crude precipitate which then washed several times with ethanol.The precipitate was dried and recrystallized from appropriate solvent.The colour for all diarylidene cyclohexanones is distinct yellow.(Table -1 and Table-2).

O x x
Table1: Names and some physical properties of (1 t -12 t ).

The sulfoxide compounds:
General procedure: ( Ghazal, 1997 ) The desired diarylidine cyclohexanone (1 mmole) was allowed to react with 10 ml of dimethylsulphoxide in a 50 ml round-bottomed flask.A drop-wise addition with stirring of 10% ethanolic NaOH cause the colour to be changed.Stirring is continued for 5 hours till the colour became dark brown (in case of no colour change the reaction mixture is refluxed for 10 min).After cooling, water is added to precipitate the corresponding products which then filtered off, washed with water then dried at r.t. and recrystallized from ethanol.(Table-3 and Table-4).It seems that the products were less soluble in DMSO than the reactants hence the reactants remained soluble in the DMSO-H 2 O mixture while the product was precipitated .
Table 3: Names and some physical properties of (13 t -24 t ).

Preliminary biological study:
In the present work, it is decided to investigate final products and study their inhibitory effect on the growth of two kinds of bacteria Grampositive (staphylococcus aureus) and Gram-negative (E.coli) by using disc diffusion method, (the standard Kirby and Bauer method) (Bauer et al., 1966).
The isolates were isolated and identified in the Dept. of Biology, College of Science, Univ. of Mosul.PROCEDURE Of each bacterial species a loopful were cultured in a nutrient broth and incubated at 37 o C for 14-16 hr, then eventually distributed on the nutrient agar by using a sterile swab.The plates were incubated at 37 o C for 30 min.
A Whatmann No. 1 type filter paper discs were distributed on the agar and a certain equal (0.01 mg/ 0.5 ml) of the compound per solvent (DMSO) was added.The controls here were Stryptomycin, Vancomycin and Gentamycin for comparison.The plates were then incubated at 37 o C for 18-24 hr.Prescott ( Prescott et al., 1996 ) method was used to illustrate the sensitivity of the studied compounds.The results were interpreted according to the report of (W.H.O.).The resistance (R) represent the diameter of inhibition zone <11 mm, while the sensitive (S) was over 16 mm, but moderately sensitive (MS) was regarded when the inhibition zone is (12-16) mm.

RESULTS AND DISCUSSION
The structures of the starting materials (1 t -12 t ) and the products (13 t -24 t ) were confirmed by (UV, IR) more over the structure of the final products were confirmed by ( 1 H-NMR) (see Tables 1-4).The biological activities of the final products (13-24 t ) had been investigated for two type of bacteria and compared with some common antibiotics like (Gentamycin, Cefodizime and Tetracycline).Compounds number (13 t , 14 t , 15 t , 16 t , 18 t , 20 t and 24 t ) showed inhibitory effects towards E. coli only, but they showed no effects towards Sta.Aueus.Also compounds (17 t , 19 t , 21 t , 22 t , and 23 t ) did n , t show any inhibitory effects towards Sta. .
According to the spectral data obtained on Tables 1-4, the suggested mechanism for the reaction of diarylidine cyclohexanones with dimethylsulphoxide (Scheme-1) may proceed via Michael or Claisen routes as indicated in the (scheme-1) (Qitto , 2008).

i-Michael route
The anion H 2 Ө CSOCH 3 may attack the β -carbon of the cyclohexanone .From the values of the heats of formation and steric energy (Table -6) it was found that (a) is more stable than (b) (scheme 1), But experimentally according to the spectral data of 1 H-NMR it was found that (b) is more favourable than (a), and hence will predominate.It seems that compounds (a) were the thermodynamically (more stable) product while compound (b) are the kinetically (more stable) product.i.e. the activation energy of path (b) is less than path (a), and hence kinetic products were predominate.

ii-Claisen route
The anion Ө CH 2 SOCH 3 may attack the carbonyl carbon via Claisen condensation to afford the intermediate C 1 .(C 1 ) may cyclize via intramolecular Michael condensation to give M 2 C 2 or lose a water molecule to afford C 2 which in turn may cyclize via intramolecular Michael condensation to produce b.Theoretically it may be concluded that the better suitable route is M 1 →M 2 C 2 →a, rather than C 1 →C 2 →b (Table 5).

Spectroscopic analysis :
The compound (13 t ) is chosen as a representative model for the spectral ( 1 H-NMR and IR) discussion.
The 1 H-NMR spectrum of compound (13 t ) showed a pentet signal at δ1.1 ppm related to the 2H of H 1 whereas the quartet signal at δ 1.35 ppm is due to the 2H at H 2 .The 2H at H 3 seemed a triplet signal at δ 1.7 ppm .But the quartet signal at δ 2.5 ppm is due to the 1H at H 4 .Another quartet signal at δ 2.7 ppm it seemed to the 1H at H 5 .The doublet signal at δ3.3 ppm correspond to 2H at H 6 .Finally a multiplet signal at δ 6.5-7.7 ppm related to the 12H of aromatic and olefinic protons.(Table 4 ) The IR spectrum of compound (13 t ) showed a band at 1598 cm -1 related to the stretching vibration of olefinic (C=C).A frequency at 1492 cm -1 , 1466 cm -1 related to the symmetrical and a symmetrical vibrations of the aromatic (C=C).But the frequency at 1067 cm -1 related to the sulfoxide group.

Table 5 :
Inhibition effect of compounds ( 13 t -24 t ) on growth of Staphylococcus aureus and Escherichia coli.