Folia Microbiol. 39 (6), 471-474 (1994)

Structure-Activity Relationships of Some 4-Quinazolylthiosemicarbazides and Their Triazolo Derivatives S. JANTOVA a, D. HUDECOVA a, K. ~PIRKOVA b, and ~. STANKOVSKY b

aDepartment of Microbiology, Biochemistry and Biology bDepartment of Organic Chemistry, Faculty of Chemical Technology, Slovak Technical University, 812 37 Bratislava, Slovakia

Received March 23, 1994 Revised version September 9, 1994

ABSTRACT. Eight 4-quinazolylthiosemicarbazides and nine of their structural analogues have been tested for antibacterial effects and for structure activity relationships. 9-Chloro-5-morpholino-l,2,4-triazolo[4,3-c]quinazoline-3-thione has demon- strated the hightest antibacterial effect (MIC of 1 mg/L for E. coli and P. mirabilis and < 1 mg/L for S. aureus and B. subtilis). The most effective derivatives have the carbon aromatic ring substituted with chlorine and the pyrimidine ring with morpholine or with secondary amine group.

The recent development in the chemistry of quinazoline derivatives has surfaced gave rise to more than five thousand publications or patents, and yielded more than one thousand derivatives (Stissl and Johne 1981). It was stimulated by the pharmaceutical utilization of some alkaloids with quinazoline skeleton, which are freely found in nature. There are four types of alkaloids, from which, e.g., febrifug- ine known as Chans-San's alkaloid was used as an antimalaricum 200 years B.C. (Wiseloge 1946). Most of these compounds were tested for their pharmacological, phytoeffectoric, biocide and other proper- ties.

Quinazoline itself (benzopyrimidine, 1,3-benzodiazine) was prepared for the first time in 1903 (Gabriel 1903) but its derivative was described even earlier by Greifs (Greifs 1869).

At present, quinazoline derivatives are used in the pharmaceutical industry, in medicine and in agriculture because of their antimicrobial (Eizohry et al. 1992), anti-inflammatory (Farghaly et al. 1990), diuretic (Pomarnacka et al. 1984), anticonvulsant (Kornet 1992), antiallergic (Peet et al. 1986), antihypertensive (Chern et al. 1991), antiparkinsonian (Naithani et al. 1989), anticancer (Renault et al. 1991) and other properties (Chaurasia 1980).

In view of the above mentioned wide-ranging effects of quinazolines, a series of these com- pounds was prepared with a 4-phenylthiosemicarbazide residue (~pirkovfi et al. 1994) in position 4. This residue was later incorporated into quinazoline as another aromatic ring. The thiosemicarbazide residue was chosen for its antibacterial and potentially anticancer or endocrine effects (Omar et al. 1981).

This study explores the relationship between antibacterial effectiveness and structure of eight 4-quinazolylthiosemicarbazides substituted both on the benzene and on the pyrimidine rings, as wcll as nine compounds derived from them, in which the original thiosemicarbazide residue makes up one part of the 1,2,4-triazole cycle condensed to quinazoline.

M A T E R I A L S A N D M E T H O D S

Materials. Bacterial strains Escherichia coli CCM 5172, Proteus mirabilis CCM 1944, Staphylo- coccus aureus CCM 3824 and Bacillus subtilis CCM 1718 were used. The preparation of the com- pounds (Scheme I) was described by ~pirkovfi et al. (1994). Treatment of 4-hydrazinoquinazoline with arylisothiocyanate yielded thiosemicarbazides (la-8a). These were heated at their melting points without a solvent, aniline was separated and 1,2,4-triazolo-[4,3-c]quinazoline-3-thiones ( lb-5b) were obtained. Treatment of some thiosemicarbazide with yellow mercury yielded corresponding 3-anilino- [4,3-c]quinazolines (2e-5c). Chromatographically pure derivatives were dissolved in dimethyl sulf- oxide; its final concentration never exceeded 1% ( V / V ) in either control or treated samples.

Antibacterial assay. In preliminary tests, the antibacterial activity of the compounds was assayed by the paper disc diffusion technique (Betina et al. 1972). 14.5 mL of a culture medium (Nutrient Broth agar) was mixed with 0.5 mL cell suspension from an overnight inoculum. The experi-

472 S. JANTOV. 't, et aL Vol. 39

merits were carried out in Petri dishes with a diameter of 150 mm. The surface of the culture medium was overlaid by discs of sterile Whatman paper no. 3 (diameter 10 mm) containing 0.1 mg of the tested derivative. The bacteria were grown statically for 1 d at 37 ~ The antibacterial activity of the com- pounds was evaluated from the diameter of the sterile inhibition zone around the centre of diffusion of the effective derivatives.

Scheme I. Survey of eompouds under study

8 X y a Z

~ ' ~ N Y ~ - Z la 6 - 0 Ph H

H 3a 6 - 0 Pi H

4a 6-Cl Pp H H N,.N....C S Sa 8-Me Ph H

H 6a 8-Me Ph NO2

l a - 8 a 7a 6-C! De H ga 6-Br Mo H

7 X lb 9-C1 Ph

9.....j~t N,~= = ~ ' ~ 2b 9-C1 Mo S 3b 9-C1 Pi

4b 9-CI Pp N~ N H 5b 7-Me Ph

l b - 5 b

7 . / ~ . . N...~Y 2c 9-CI Mo

X -"~C-" ")[- " | 3e 9-CI Pi

9 t,,'x._/~,,~ "~NC~N'x,/,-- H N S04e 7-Me9"Cl PhPP

- - \Ph

2 c - 5 c

aph - phenyl; Mo - morpholinyl; Pi - piperidinyl; Pp - 4-phenylpiperazinyl; De - diethylamino

Minimum inhibitory concentration (MIC) for the derivatives with antibacterial activity was determined by the dilution technique. The effect was determined during reciprocal culturing of 7 mL of the Miiller-Hinton medium into which 0.5 mL suspension of the tested bacteria (from an overnight inoculum) was added together with 75 laL of the tested derivative (concentrations 200; 100; 10; 1 and 0.1 mg/L were used). The values of the MIC were determined from the toxicity curves.

RESULTS AND DISCUSSION

The results of the preliminary screening are summarized in Table I. The broadest antibacterial spectrum was found with derivative 2b which was effective with all tested bacteria. A certain antibacte- rial effect on G § and G- bacteria was manifested by derivatives 6a and 4b. The quinazoline deriva- tives 5a, 2e and 3c influenced only the G - bacterium E. coli. The other derivatives were inactive against all bacteria used. Sensitivity of G § bacteria to the derivatives is higher than that of G- bacteria.

The MIC values of selected derivatives are given in Table II. 9-Chloro-5-morpholino-l,2,4-tri- azolo-[4,3-c]quinazoline-3-thione (2b) exhibited the highest antibacterial effect.

1994 STRUCTURE-ACTIVITY RELATIONSHIPS OF SOME 4-QUINAZOLYLTHIOSEMICARBAZIDES 473

T a b l e I. Antibacterial activity (diameter of the sterile inhibition zone, mm) of the tested compounds 1-8

Compound a E. coli P. mirabilis S. aureus B. subtilis

5 a 1 8 - - -

6 a 2 0 - - 2 0

2 b 1 8 1 8 1 8 2 2

4 b 1 6 - 1 4 -

2 r 14 - - -

3 r 1 6 - - -

aother tested compounds were inactive (no sterile inhibition zone was formed).

F r o m the eight 4-quinazolyl thio- semicarbazides ( l a - 8 a ) studied, only two were active (5a, 6a). In bo th cases the quinazol ine skele ton was subst i tuted in the a romat ic r ing by the methyl g roup and in the pyr imidine ring by the phenyl group. F r o m these derivatives only the ni- t ro-derivat ive 6a was active against bo th G § and G - bacter ia . However , in analogues of 4-quinazolyl thiosemi- carbazides, ( l b - 5 b , 2 c - 5 c ; Table I) this s tructural combina t ion is not active.

F r o m the five tested thiones ( l b - 5 b ) only 2 b and 4 b demons t ra t ed ant ibac ter ia l activity. Active compounds have the carbon a romat ic ring substi tuted with chlor ine and the pyr imidine ring with morpho l ine (2b) or with 4-phenylpiperazine.

A m o n g the third type of compounds , t r iazoles 2 c - 5 e , active were those which had chlorine and a secondary amino group as subst i tuents (2e, 3c).

Our resul ts imply that no unequivocal conclu- sions can be drawn about Table II. MIC values (rag/L) of selected active compounds

the influence of a substi tut- ion type on bac ter ia l activity. Compound a E. coli P. mirabilis S. aureus B. subtilis

Hence, the quinazolylthio- semicarbaz ide grouping as 6a 10 >200 >200 1 such is p robab ly responsible 2b 1 1 1> MIC >0.1 1> MIC >0.1

for the ant ibacter ia l activity, essential ly regard less of the avalues MIC of compounds 5a, 4b, 2r and 3c being 10 < MIC < 100 mg/L.

type of subst i tut ion in the a romat ic or pyr imidine ring, or of the posi t ion of the th iosemicarbaz ide residue.

Our da ta indicate that 9-chloro-5-morphol ino- l ,2 ,4- t r iazolo-[4 ,3-c]quinazol ine-3- thione (deriv- ative 2b ) can be used as a new potent ia l ly ant ibacter ia l substance.

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