Synthesis, Characterization of Substituted 3-Cyanopyrroles and Evaluation of Antimicrobial Activity.

 

Pawar Rupali Rajaram*, Mohite Shrinivas Krishna

R.C.P. Kasegaon, Sangli, (Maharashtra) India., India

 *Corresponding Author E-mail: pawarrupali75@gmail.com

 

A straightforward simple synthesis of substituted 3-cyanopyrroles using Paal–Knorr method has been accomplished with a satisfactory yield. The Paal–Knorr pyrrole synthesis, which involves the reaction of dicarbonyls with amines, is among the most classical methods of heterocyclic pyrrole ring synthesis. The detailed sequence and the nature of the intermediates that occur in the Paal–Knorr reaction mechanism are not well understood. This method produces pyrroles with multicyclic aromatic amines. A series of substituted 3-cyanopyrrole derivatives were evaluated for anti-inflammatory and antimicrobial activity.

 

 

INTRODUCTION:

Pyrroles are an important class of compounds with different biological activities. The Paal-Knorr reaction is considered to be the most attractive method for the synthesis of pyrroles¹. Pyrrole derivatives are nitrogen containing heterocyclic compounds which constitute the backbone of many biologically active compounds and natural products such as chlorophyll, hemoglobin, myoglobin, cytochromes, and vitamins². A number of clinically used medicines with antibacterial, antiviral, anti-inflammatory, antitumoral or antioxidant properties carry out the pyrrole moiety in their fundamental structures³. They have good antitubercular activity⁴. There is great interest in pyrrole derivatives as antimicrobial agents. Bromo substituted Pyrroles have proved to be effective against S. aureus, B. subtilis and E. coli and interesting antifungal activity against C. albicans as shown by Petruso et al.⁵

 

MATERIALS AND METHODS:

Chemicals:

All chemicals and solvents were procured from commercial sources, purified and dried using standard procedures whenever required. The reagents were purchased from Research-Lab Islampur, Loba Chemie Pvt. Ltd. Mumbai, Himedia Laboratories Ltd., Kolhapur.

 

EXPERIMENTAL^6-9-

A)                  Synthesis of 2-amino-4,5-diphenyl-1-substituted -1H-pyrrole-3-carbonitriles I(A-C)-

A mixture of benzoin (2.12 g, 0.01 mol), the appropriate amine [2,4-dinitroaniline (1.83 g, 0.01 mol) A,                   4-bromoaniline (1.72 g, 0.01 mol) B and 2-methoxyaniline (1.28 g, 0.01mol) C] and conc. HCl (6–8 drops) in ethanol (40 ml) was heated under reflux for 8 hrs and cooled. Malononitrile (0.66 mg, 0.01 mol) was added, followed by a catalytic amount (1.5 ml) of pyridine portionwise and refluxed for about 4 hrs. Kept in refrigerator so as to obtain fine crystals and was recrystallized from hot methanol.

 

 

Fig No: 1 Synthesis of substituted 3-cyanopyrroles I(A-C)

 

 

B)      Synthesis of derivatives-

a)       Synthesis of N-(1-aryl-3-cyano-4,5-diphenyl-1H-pyrrol-2-yl)-acetamides II(A₁-C₁)-

The appropriate aminopyrrole, (4.25 g, 0.01 mol) IA, IB (4.14 g, 0.01 mol) and IC (3.65 g, 0.01 mol), in acetic anhydride (40 ml) was refluxed for 4 h, cooled, poured onto ice-water, neutralized with ammonia to give compounds, II(A₁-C₁) respectively in the form of precipitates which were filtered off, dried, and recrystallized from methanol.

 

b)       Synthesis of 5,6-diphenyl-7-substituted-7H-pyrrolo[2,3-d]pyrimidin-4-yl-amines III(A₂-C₂)-

A mixture of the appropriate aminopyrrole, (4.25 g, 0.01 mol), IA, (4.14 g, 0.01 mol) IB and (3.65 g, 0.01 mol) IC, and formamide (30 mL, 0.066 mol) was heated under reflux for 6 h, cooled and poured onto ice-water to give precipitates, which were filtered off, dried, and recrystallized from ethanol to yield compounds III(A₂-C₂), respectively.

 

c)       Synthesis of 2-amino-1-aryl-4,5-diphenyl-3-tetrazolo-1H-pyrroles IV(A₃-C₃)-

A mixture of the appropriate cyanopyrrole, (4.25 g, 0.01 mol) IA, (4.14 g, 0.01 mol) IB and (3.65 g, 0.01 mol) IC, sodium azide (0.65 g, 0.01 mol) and ammonium chloride (1.06 g, 0.02 mol) was refluxed in DMF (30 mL) for 4 h, filtered while hot and the residue was washed with hot DMF. The collected filtrate was concentrated, cooled, poured onto ice--water to yield precipitates, which were filtered, dried and recrystallized from methanol,

to give compounds IV(A₃-C₃), respectively.

 

 

Fig No: 2 Synthesis of derivatives of substituted 3-cyanopyrroles

 

Physico-chemical data of the all synthesized compounds is given in Table No 1.

Table No. 1: Physico-chemical data of the compounds

Sr. No	Comp. No	R	Molecular weight	Yield (%)	M.P. 0C	Rf	Mobile Phase
1.	IA	2,4-NO2	425.40	61.65	188-190	0.64	T:EA:W(7.8:2:0.2)
2.	IIA1	2,4-NO2	467.43	47.53	138-140	0.60	T:EA:W(7.8:2:0.2)
3.	IIIA2	2,4-NO2	451.43	58.35	200-202	0.50	T:EA:A(7.5:2:0.5)
4.	IVA3	2,4-NO2	469.45	51.61	138-140	0.56	T:EA (8:2)
5.	IB	4-Br	414.29	51.82	218-220	0.59	T:EA:W(7.8:2:0.2)
6.	IIB1	4-Br	456.33	59.21	196-198	0.73	T:EA:W(7.8:2:0.2)
7.	IIIB2	4-Br	441.32	52.60	156-158	0.64	T:EA:A(7.5:2:0.5)
8.	IVB3	4-Br	458.35	62.88	184-186	0.58	T:EA (8:2)
9.	IC	2-OCH3	365.42	49.31	164-166	0.67	T:EA:W(7.8:2:0.2)
10.	IIC1	2-OCH3	407.46	54.54	172-174	0.60	T:EA:W(7.8:2:0.2)
11.	IIIC2	2-OCH3	492.45	49.87	220-222	0.62	T:EA:A(7.5:2:0.5)
12.	IVC3	2-OCH3	408.45	53.94	206-208	0.66	T:EA (8:2)

 

Spectral analysis of the newly synthesized compounds is given in Table No 2.

Table No. 2: Spectral analysis of the newly synthesized compounds

Comp. No	Mass m/z	IR (cm-1)	1HNMR (ppm)
IA	425 (33.9%) 426 [M++1]	2242.21 (CN), 1576.44 (N-O), 3453.41 (NH2)	7.197 -8.781 (m, 13H, Ar-H), 5.045 (s, 2H, NH2)
IIA1	467 (36%) 469 [M++2]	2261.54 (CN), 1595.81 (N-O), 3480.06 (N-H)	7.317-8.541 (m, 13H, Ar-H), 2.791 (s, 3H, CH3-C=O), 8.832 (s, 1H, NH,)
IIIA2	451 (100%) M+	3415.03 (NH), 1590.02 (N-O),	7.581-8.352 (m, 13H, Ar-H),  8.546 (s, 1H, C-2H), 5.201 (s, 2H, NH2)
IVA3	469 (27%) 471 [M++2]	3495.07 (NH), 1502.28 (N-O), 1585.81 (N=N)	7.178-8.974 (m, 13H, Ar-H),  8.587 (s, 1H, NH), 5.211 (s, 2H, NH2,)
IB	414 (43.6%) M+	2258.69 (CN),633.501 (C-Br), 3451.96 (N-H)	6.957-7.847 (m, 14H, Ar-H),5.173 (s, 2H, NH2 )
IIB1	456 (27.3%) 458 [M++2]	2212.74 (CN), 604.87 (C-Br), 1633.15(C=O)	7.389-8.135 (m, 14H,Ar-H),2.137 (s, 3H, CH3-C=O),8.436 (s, 1H, NH)
IIIB2	441 (17%) 442 [M++1]	604.88 (C-Br), 3481.06 (N-H)	7.032-8.278 (m, 14H,Ar-H), 8.589 (s, 1H, C-2H),5.136 (s, 2H, NH2)
IVB3	458 (28%) 459 [M++1]	596.86 (C-Br), 1597.73 (N=N), 3441.35 (N-H)	7.968-8.231 (m, 14H,Ar-H),8.526 (s, 1H, NH),5.379 (s, 2H, NH2)
IC	365 (45.5%) 367 [M++2]	2212.74 (CN), 1260.22 (C-O), 3449.22 (N-H)	6.848-7.723 (m, 14H,Ar-H),3.791 (s, 3H, OCH3),4.915 (s, 2H, NH2)
IIC1	407 (12.7%) 408 [M++1]	2259.48 (CN), 1250.61(C-O) 1683.55 (C=O), 3383.50 (N-H)	6.819-7.743 (m, 14H,Ar-H),2.134 (s, 3H, CH3-C=O), 8.163 (s, 1H, NH), 3.782 (s, 3H, OCH3)
IIIC2	492 (11.2%) 494 [M++2]	1286.29 (C-O),  3423.99 (N-H)	6.814-7.592 (m, 14H,Ar-H),8.432 (s, 1H, C-2H), 5.189 (s, 2H, NH2), 3.768 (s, 3H, OCH3)
IVC3	408 (41.5%) M+	1216.86 (C-O), 1594.84 (N=N)	6.849-7.756 592 (m, 14H,Ar-H), 8.389 (s, 1H, NH), 5.394 (s, 2H, NH2), 3.812 (s, 3H, OCH3)

 

PHARMACOLOGICAL RESULTS:

All successfully synthesized compounds by Paal knorr mechanism were screened for their in vitro antimicrobial activity against two representative Gram-positive and Gram-negative bacterial strains and against a human pathogen fungal strain. The results expressed in MIC values (minimum inhibitory concentration) are reported in Table 3 along with the activity of Amoxicillin and Fluconazole for comparison.

 

Table No. 3: Antimicrobial activity of newly synthesized compounds (MIC µg ml^-1)

Sr. No	Comp. No	B. subtilis	S. aureus	E. coli	C. albicans
1.	IA	40	80	320	640
2.	IIA1	80	40	-	-
3.	IIIA2	40	-	640	1280
4.	IVA3	-	20	-	-
5.	IB	20	80	160	640
6.	IIB1	160	160	320	160
7.	IIIB2	40	20	-	320
8.	IVB3	80	80	160	-
9.	IC	-	-	640	640
10.	IIC1	80	40	-	-
11.	IIIC2	-	-	320	-
12.	IVC3	20	40	-	-
13.	Amoxicillin	80	40	320
14.	Fluconazole	-	-	-	640

 

DISCUSSION:

Bacillus substilis and Staphylococcus aureus were used as representative of gram positive bacteria. Compounds IA, IIIA₂, IB, IIIB₂, andIVC₃ were two times more active against Bacillus substilis, compound IIIB₂, and IVA₃  were two times more active  against Staphylococcus aureus than Amoxicillin. In case of gram negative species Escherichia coli, compound IIB and IIC showed highest activity used for screening, which is also more than standard used for antibacterial activity. CompoundS IB₁ and IIIB₂ were found to be two times as active as Fluconazole against Candida albicans

 

CONCLUSION:

We have synthesized a series of Cyanopyrroles, Pyrrolo-pyrimidines and tetrazolo substituted pyrroles by Paal knorr mechanism and evaluated for its antimicrobial activity. The bromine substituted compounds¹⁰ at N-1 of pyrroles reveals greater antimicrobial activity.

 

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Received on 12.07.2013          Modified on 25.07.2013

Accepted on 28.07.2013         © AJRC All right reserved