Synthesis of Some Thiazino-pyrazoles as Potential Fungicides

Introduction

Pyrazole derivatives possess diverse chemical reactivity and broad spectrum of biological activities . A number of substituted pyrazoles are used as fungicides, insecticide, pesticides, herbicides in the field of agriculture ^(1,2). They are used as colouration of paints, varnishes, lacquers in the field of industry ^(3,4) . These derivatives are used as anti-oxidant⁽⁵⁾ for rubber , linseed oil and  as disperse dyes ⁽⁶⁾. They possess wide range of pharmacological activities as hypoglycemic⁽⁷⁾, antimicrobial^(8,9), anticonvulsive⁽¹⁰⁾, anti-inflammatory⁽¹¹⁾, antihistaminic⁽¹²⁾, anti coagulant⁽¹³⁾, and anti-rheumatic⁽¹⁴⁾ agents etc. Some thiazino-pyrazole derivatives have  been synthesized and screened their antimicrobial activity^(15-17). In continuation of our study an attempt is to synthesize some new derivatives of thiazino-pyrazole and screened their fungicidal activity against both the test fungi A. fumigatus and C. albicans at different concentration viz, 1000,100 & 10 ppm.

2,4-dihydro-2-arylthioanilido-5-methyl-3H-pyrazol – 3 – ones (1) were synthesised by the reaction of ethylacetoacetate and aryl thiosemicarbazide. The compound (1) was condensed with aromatic aldehyde in presence of glacial acetic acid to give 4-arylmethylene –  2, 4-dihydro- 2- arylthioanilido -5-methyl-3H-pyrazol-3-ones(2).The compound(2) was refluxed with phenyl thiourea in presence of alcoholic KOH for 3-4 hrs to give 1-arylthioanilido-3-methyl-4-aryl-6-phenylimino-4,7-dihydro-1,3-thiazino[5,4-d]pyrazoles(3)(Scheme-1).

Scheme 1 Click here to View scheme

 

Experimental

Melting points were taken in an open capillary tube and are uncorrected. The IR spectra were recorded in KBr disc on Perkin-Elmer-720 spectrophotometer. The ¹H NMR spectra were recorded in CDCl₃ /DMSO-d₆ on Varian A-60D spectrophotometer. The chemical shifts are recorded in d ppm down field from TMS, which are used as an internal standard.

2,4-Dihydro-2-arylthioanilido-5-methyl-3H-pyrazol-3-ones(1):

These pyrazolones were prepared by known method^(18,19).

4-Arylmethylene – 2,4-dihydro- 2-arylthioanilido-5-methyl-3H-pyrazol –  3-ones(2):

A mixture of compound (1)(0.01mol), aromatic aldehyde (0.01 mol) and sodium acetate (0.011 mol) was refluxed in glacial acetic acid for 2h. The reaction mixture was cooled and poured in cold water to give solid materials. The resulting solid was recrystallised from ethanol.

1-Arylthioanilido-3-methyl-4-aryl-6-phenylimino-4,7-dihydro-1,3-thiazino[5,4-d]pyrazoles(3):

These were prepared by know method⁽²⁰⁾.A mixture of compound (2) (0.01 mol), potassium hydroxide (0.02 mol) and phenyl thiourea (0.01 mol) was refluxed for 3-4 h in ethanol. After evaporating the solvent , it was then acidified with dilute hydrochloric acid to give solid materials. The resulting solid was recrystallised from ethanol. The physical and spectral data of all synthesised compounds (3a-o) are given in the table-1.

Table 1

Comp. No.	R	R|	M.P. (0c)	Yield (%)	I.R. (KBr disc) cm–1, nmax	PMR (CDCl3) d (ppm)
3a	H	H	158	65	3510(NH), 3390(=NPh), 1530(C=N),1230(C=S)	2.0(3H,s,CH3), 4.2(1H,s,S-CH), 6.9-7.6(15H,m,ArH), 8.6(2H,s,NH)
3b	H	p-NO2	178	61	3515(NH), 3395(=NPh), 1535(C=N),1235(C=S)	2.1(3H,s,CH3), 4.0(1H,s,S-CH), 6.8-7.8(14H,m,ArH), 8.8(2H,s,NH)
3c	H	p-N(Me)2	182	72	3518(NH), 3398(=NPh), 1538(C=N),1234(C=S)	2.3(3H,s,CH3),3.0(6H,s,NMe2), 4.1(1H,s,S-CH), 6.9-7.8(14H,m,ArH) , 8.9(2H,s,NH)
3d	H	p-Cl	195	68	3505(NH), 3390(=NPh), 1532(C=N),1230(C=S)	2.0(3H,s,CH3), 4.3(1H,s,S-CH), 6.8-7.5(14H,m,ArH), 8.8(2H,s,NH)
3e	H	p-OH	214	70	3580(OH), 3520(NH), 3390(=NPh), 1535(C=N),1238(C=S)	2.0(3H,s,CH3), 4.1(1H,s,S-CH), 6.5(1H,s,OH), 7.0-7.5(14H,m,ArH), 8.9(2H,s,NH)
3f	p–CH3	H	157	62	3525(NH), 3395(=NPh), 1540(C=N),1236(C=S)	2.1(3H,s,CH3), 3.4(3H,s,ArCH3), 4.4(1H,s,S-CH), 7.1-7.9(14H,m,ArH), 8.7(2H,s,NH)
3g	p–CH3	p-NO2	179	64	3514(NH), 3398(=NPh), 1545(C=N),1238(C=S)	1.9(3H,s,CH3), 3.2(3H,s,ArCH3), 4.3(1H,s,S-CH), 7.2-8.0(13H,m,ArH), 8.9(2H,s,NH)
3h	p–CH3	p-N(Me)2	193	69	3515(NH), 3395(=NPh), 1535(C=N),1235(C=S)	1.8(3H,s,CH3), 3.0(6H,s,NMe2), 3.5(3H,s,ArCH3), 4.6(1H,s,S-CH), 7.1-7.6(13H,m,ArH), 8.6(2H,s,NH)
3i	p–CH3	p-Cl	202	70	3520(NH), 3390(=NPh), 1542(C=N),1236(C=S)	2.1(3H,s,CH3), 3.3(3H,s,ArCH3), 4.1(1H,s,S-CH), 6.9-7.9(13H,m,ArH), 8.7(2H,s,NH)
3j	p–CH3	p-OH	218	72	3585(OH), 3508(NH), 3398(=NPh), 1538(C=N),1240(C=S)	2.2(3H,s,CH3), 3.4(3H,s,ArCH3), 4.2(1H,s,S-CH), 6.4(1H,s,OH), 7.2-7.7(13H,m,ArH), 8.8(2H,s,NH)
3k	p–OCH3	H	154	68	3505(NH), 3390(=NPh), 1545(C=N),1245(C=S)	1.9(3H,s,CH3), 3.7(3H,s,OCH3), 4.3(1H,s,S-CH), 7.1-7.9(14H,m,ArH), 8.6(2H,s,NH)
3l	p–OCH3	p-NO2	165	65	3512(NH), 3380(=NPh), 1548(C=N),1250(C=S)	1.8(3H,s,CH3), 3.8(3H,s,OCH3), 4.4(1H,s,S-CH), 6.9-7.8(13H,m,ArH), 8.7(2H,s,NH)
3m	p–OCH3	p-N(Me)2	186	68	3528(NH), 3384(=NPh), 1530(C=N),1255(C=S)	2.2(3H,s,CH3), 3.1(6H,s,NMe2), 3.7(3H,s,OCH3), 4.1(1H,s,S-CH), 7.2-8.0(13H,m,ArH), 8.8(2H,s,NH)
3n	p–OCH3	p-Cl	219	73	3505(NH), 3380(=NPh), 1540(C=N),1258(C=S)	2.1(3H,s,CH3), 3.6(3H,s,OCH3), 4.5(1H,s,S-CH), 6.9-8.0(13H,m,ArH), 8.6(2H,s,NH)
3o	p–OCH3	p-OH	207	71	3590(OH), 3500(NH), 3382(=NPh), 1545(C=N),1260(C=S)	2.0(3H,s,CH3), 3.5(3H,s,OCH3), 4.6(1H,s,S-CH), 6.4(1H,s,OH), 7.2-8.0(13H,m,ArH), 8.8(2H,s,NH)

 

Antifungal Activity

All the thiazino-pyrazoles (3a-o) were screened for their antifungal activity against Aspergillus fumigatus and Candida albicans by using food poisoning of solidified agar techniques at various concentration viz. 1000, 100 and 10 ppm by the standard method⁽²¹⁾.

The inhibition of the fungus growth was determined as the difference in growth between test and control plates. The percentage inhibition in the colony of the test fungus was expressed as – 

Percentage inhibition (%) = (C–T) × 100/C

where   C – diameter of fungus colony (mm) in control plates.

T – diameter of fungus colony (mm) in treated plates.

The antifungal activity in terms of percentage inhibition shown by thiazino-pyrazoles (3a-o) has been listed in the Table 2.

 

Table 2

Comp. No.	Substituents		Average % inhibition after 96 hours
	R	R|	Organism A. fumigatus concentration (ppm) used			Organism C. albicans concentration (ppm) used
			1000	100	10	1000	100	10
3a	H	H	56.4	47.2	36.2	55.2	46.0	35.2
3b	H	p-NO2	59.2	49.4	39.4	58.0	48.2	38.2
3c	H	p-N(Me)2	60.4	50.2	40.8	59.2	49.2	39.6
3d	H	p-Cl	62.6	52.2	42.8	61.4	50.0	40.8
3e	H	p-OH	55.2	44.4	35.2	54.0	43.2	34.4
3f	p–CH3	H	55.0	46.0	35.0	54.8	45.8	34.2
3g	p–CH3	p-NO2	58.0	48.2	38.2	57.6	47.2	37.2
3h	p–CH3	p-N(Me)2	59.2	49.4	39.4	58.0	48.2	38.2
3i	p–CH3	p-Cl	61.6	51.8	41.2	60.4	49.4	39.0
3j	p–CH3	p-OH	54.2	42.6	34.0	53.0	41.2	33.2
3k	p–OCH3	H	54.0	45.8	34.2	53.8	44.4	33.4
3l	p–OCH3	p-NO2	56.8	47.0	37.4	55.6	46.2	36.0
3m	p–OCH3	p-N(Me)2	57.4	48.8	38.2	56.2	47.4	37.8
3n	p–OCH3	p-Cl	60.4	50.2	39.8	59.2	48.0	38.2
3o	p–OCH3	p-OH	53.2	40.2	33.2	52.0	40.2	31.8
Bavistin			99.4	95.0	90.0	99.2	95.0	90.0

Result and Discussion

It was observed from the antifungal screening data that all the compounds (3a-o) show antifungal activity against both the test fungi A. fumigatus and C. albicans. It was also observed that the fungicidal activity of all synthesised compounds decreased upon dilution,so that all the compounds show greater fungitoxicity as the concentration increased . Structure activity relationship  have demon- strated that the  electron  withdrawing   group     (deactivating group)

increase the fungicidal activity and electron donating group (activating group) decrease the fungicidal activity⁽²²⁾. The compounds having p-Cl group (3d) inhance the antifungal activity  than the p-N(Me)₂ group (3c). Since p-Cl group is electron withdrawing group and p-N(Me)₂ group is electron donating group. Similarly  we compare the compounds having p-NO₂  group (3b) inhance the fungicidal activity than the     p-OH group (3e) . Over all result in my experiment from antifungal screening data that the p-Cl group inhance the fungicidal activity than p-NO₂ & p-N(Me)_2.

Acknowledgement

The authors are very grateful to Dr. U. P. Singh, Principal and the Head , Deptt. of chemistry , T.D.P.G.College, Jaunpur (U. P.) for providing necessary facilities.

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