Surface active properties and biological activity of novel nonionic surfactants containing pyrimidines and related nitrogen heterocyclic ring systems

A series of annelated pyrimidine derivatives has been synthesized via different heterocyclization reactions of suitably functionalized 6-(4-octadecyloxyphenyl)-4-oxo-2- thioxo-1,2,3,4-tetrahydropyrimidine-5-carbonitrile (4) with different electrophiles and nucleophiles. These heterocycles bear an active hydrogen atom (NH, OH or COOH) which could be propoxylated using propylene oxide with different moles, 5, 10 and 15, to produce nonionic surfactant having a long alkyl chain with molecular weight suitable for becoming an amphiphilic molecule with correct hydrophilic-lypophilic balance which enhances solubility, biodegradability and hence lowers the toxicity to human beings and becomes environmentally friendly. In addition, the antimicrobial activities of these compounds were screened and it was found that some of these compounds have similar or higher activity compared with commercial antibiotic drugs (sulphadiazine), which make them suitable for diverse applications like the manufacturing of drugs, pesticides, emulsifiers, cosmetics, etc.


INTRODUCTION
In continuation of our syntheses of surface active agents containing a heterocyclic moiety (Amin et al., 2004;El-Sayed et al., 2005a;Amin et al., 2006;Eissa and El-Sayed, 2006;El-Sayed, 2006), it was interesting to prepare some biologically active heterocycles which constitute an important class of organic compounds with diverse biological activities.Numerous fatty alcohols are now more available in their pure form and inexpensive enough to provide the chemical field with a wealth of reactions in which fatty alcohols are used as raw material in a variety of industrial products like pharmaceuticals, cosmetics, surfactants, paints,… etc. Pyrimidine nucleus is considered one of the most important classes of chemotherapeutic drugs especially among those which are used in large scale for the treatment of cancer and tumors (Xu et al., 2004), antiviral (Eman and Mohamed, 2004), antihistaminic (Maisa et al., 2004), analgesic activities (Aly and Nassar, 2004) and other pharmaceutical activities (Yvette and Aly, 2003)) in current medicinal use.In particular, our interest in developing an efficient syntheses of polyfunctionally substituted heterocycles using the readily obtainable pyrimidine as starting material from fatty alcohols motivated us to explore their potential use for the synthesis of polyfunctionally substituted pyrimidine derivatives useful for optimization of their biological activity.This encouraged us to continue our progress in applying octadecanol as starting material for synthesizing some new biologically active pyrimidine and fused pyrimidine derivatives.These compounds fulfill the following two requirements.First, an amphiphilic molecule must contain both a hydrophobic and a hydrophilic part.Second, the resence of active Hatoms, (NH, SH, OH and COOH) in the molecule which make the propyloxylation possible leading to the hydrophobic part in a desired hydrophilichydrophobic balance (Chaudlhuri et al., 1987).

MATERIALS AND METHODS
Melting points are uncorrected.IR spectra in KBr were measured on a Pye-Uncam SP-1000 infrared spectrophotometer on a KBr disk or nujol.The 1 HNMR spectra were obtained on a Varian EM-390-60 MHz spectrometer in (D 6 ) DMSO as the solvent, tetramethylsilane (TMS) served as an internal reference and chemical shifts are expressed as δ (ppm).Microanalyses were preformed by the Micro analytical Unit at Cairo University.Antimicrobial and antifungal activity tests were carried out by the microbiology laboratory, Faculty of Science, Benha University, Egypt.

Conversion of the prepared compounds to nonionic surfactants
Nonionic surfactants are prepared by the addition of n moles of propylene oxide (n = 5, 10, 15) to one mol of suitable product using KOH as catalyst.A complete description of the procedure is given in (Morgos et al., 1983a).The addition of propylene oxide gave a mixture of propenoxylated products whose structures were confirmed by IR and 1 HNMR spectra.IR spectra showed two broad bands at 1100 and 950 cm -1 characteristic for νC-O-C ether linkage of polypropenoxy chain and 1 HNMR spectra showed the protons of propenoxy groups δ = 3.2-3.7 (m, -CH 2 CH(CH 3 )-O)-.
2.3.2.Cloud point was determined by gradually heating a surfactant solution (1.0 wt %) in a bath of controlled temperature, and recording the temperature at which the clear, or nearly clear solutions become definitely turbid.The reproducibility of this temperature was checked by cooling the solutions until they become clear again (Wiel et al., 1963).

Wetting time was determined by
immersing a sample of cotton fabric in 1.0 wt % aqueous solution of surfactants (Draves and Clarkso, 1931).
2.3.4.Foaming properties were measured according to (El-Sukkary et al., 1987).In this procedure a 25 ml solution (1.0 wt %) was shaken vigorously for 10 seconds in a 100 ml graduated cylinder with a glass stopper at 25 o .The solution was allowed to stand for 30 seconds and then the foam height was measured.2.3.5.Emulsification stability was prepared from 10 ml of a 20 mmol aqueous solution of surfactant and 5 ml of toluene at 40 o .Emulsion stability was determined as the time which 9 ml of aqueous layer took to separate from the emulsion counting since cession of shaking (Takeshi, 1970).

Biodegradability
Biodegradability was evaluated by surface tension measurements which were taken each day, on each sample during the degradation test.Biodegradation percent (D) (Eter et al., 1974) for each sample was calculated using the following equation: D = [(γ t -γ o ) / (γ bt -γ o )] x 100, where γ t = surface tension at time t, γ o = surface tension at zero time, γ bt = surface tension of blank experiment at time t (without sample).

Biological activity
The biological activities of these compounds have been evaluated by filter paper disc method (Rosen, 1989).After dissolving in N,N-dimethylformamide to obtain a 1mg/mL solution (1000 ppm).The inhibition zones of incubation period of 3 days at 37 o for Echerichia coli and 28 o for other bacteria and fungi were recorded.N, N-Dimethylformamide alone showed no inhibition zone.
Of particular interest is a cyclocondensation reaction of thienopyrimidine 11 with phenyl isothiocyanate which resulted in the formation of the tricyclic heterocycle 12.

Conversion of the prepared compounds (4-16) to nonionic surfactants (17a-c to 28a-c)
Propylene oxide condensation is one of the principal processes employed to introduce a hydrophilic functional group into organic compounds.The ultimate objective of the process is the production of surface active agents having the desired hydrophile-lipophile balance for such commercial applications such as detergents, emulsification, wetting and textile processing (Ahmed, 2004).One of the most important groups of surfactants with growing industrial interest is the nonionic, which can be synthesized by propoxylation with the propylene oxide of compounds, which contain XH groups in the presence of KOH as a catalyst, as the following equation R is a long chain aliphatic hydrocarbon (C 18 ); XH is OH, SH, COOH, NH, NH 2 and (n) the moles of propylene oxide (n = 5, 10, 15 mole) reacted with one mole of starting molecules.The addition of propylene oxide gave nonionic surfactants (17a-c to 28a-c).The reaction conditions are illustrated in Table 1.Scheme 3 shows the propenoxylation of compounds 4 and 11 as an example.

Surface active properties
Nonionic surfactants find diverse applications, both in industry and in the home.Their moderate foaming and good detergency are employed in a variety of ways in the leather industry, accelerated soaking and liming are improved by the addition of wetting agents (El-Dougdoug and Ahmed, 2004).The study of the surface active properties of the oxypropylated compounds has been done in an aqueous solution (1wt %, pH = 7) at 25 o .The surface activity and related properties of the synthesized compounds including surface and interfacial tension, cloud point, wetting time, foaming and emulsification properties are given in Table 2.

Surface and interfacial tension
The surface and interfacial tension of the prepared compounds are shown in Table 2.It can be observed that the alkyl chain length gives rise to increased hydrophobic interaction between the alkyl chains and also to increased hydrophobic hydration effects that in turn may reduce the surface tension which provide these compounds with pronounced surface activity.

Cloud point
A very important factor in making the most efficient use of nonionic surfactants in an aqueous 114 GRASAS Y ACEITES, 59 (2), ABRIL-JUNIO, 18-28, 2008, ISSN: 0017-3495  system is an understanding of the property called cloud point.All these compounds showed high cloud points which gave performance in hot water and it was increased by increasing the number of the propoxy group.

Wetting time
All the prepared compounds showed a decrease in wetting time with an increase in the number of propylene oxide units in the molecule.Moreover, the presence of propylene oxide in different moles caused a reduction in wetting time, i.e. improving their wetting properties which make widely applicable in the textile industry (Somaya et al., 1998).

Foam properties
Nonionic surfactants containing an aromatic ring such showed poor foaming properties.The foam height of the prepared surfactants increases with an increase in the number of propylene oxide units per molecule of surfactant.The low foaming power could have an application in the dyeing auxiliary industry (Morgos et al., 1983b).

Emulsion stability
Emulsification is one of the most important properties of surfactants.In many textile processes such as scouring and dyeing, it is necessary to introduce surfactants into the bath to remove oily impurities from the fibers.On the other hand, nonionic surfactants with good emulsion stability have been used in such fields as, shampoos, cosmetics, emulsion paints and the textile industry.The results in Table 2 showed that the emulsion stability increases by decreasing the number of propylene oxide units.

Biodegradability
The trend of degradation in river die-away tests was followed by surface tension measurements.The results are given in Table 3.The rate of degradation of these compounds depends on the size of the molecule; a bulky molecule diffuses through the cell membrane, and its degradation is more difficult.This means that molecules with a low proportion of propylene oxide are more easily degraded than those containing a higher proportion.

Biological activity
All the prepared compounds were screened for their activity against Gram-positive bacteria (Staphyloccus aureus, Bacillus subtilis, Bacillus cereus), Gram-negative bacteria (Pseudomonas aurignosa, Echerichia coli, Enterobacter aerogenes), as well as fungi (Aspergillus niger, Penicillium italicum, Fusarium oxysporum).Also, a comparison between the activity of our synthesized compounds and sulphadiazine as standard drug was discussed.The results are listed in Tables 4 and 5.It is apparent from Table 4 that some of the synthesized compounds showed antibacterial activity.
pyridine (20 ml) and a few drops of H 2 O was heated under reflux for 12 h.The mixture was poured onto ice-cold HCl.The product was obtained by filtration and crystallized from EtOH to give 16.

Table 2 Surface properties of nonionic compounds a
n in the number of propylene oxide added to the chosen compound.SURFACE ACTIVE PROPERTIES AND BIOLOGICAL ACTIVITY OF NOVEL NONIONIC SURFACTANTS CONTAINING PYRIMIDINES… a Error was: Surface and interfacial tensions = Ϯ 0.1 dynes/cm; Cloud point = Ϯ 1 o C; foam height = Ϯ 2 mm; Wetting time = Ϯ 1 sec; emulsion = Ϯ 1 min.b

Table 4 Antibacterial activity of the prepared compounds
a Error of calculations was: Biodegradation rate = ± 0.5 %.