INTRODUCTION:

So far as it is known that no derivatives of cinnoline occurs in nature. The cinnoline ring system was discovered in 1883 by Von Richer^1-9. Who in the course of experiments designed to convert O-nitro phenyl propionic acid into O-hydroxy acetophenone found that the diazonium chloride derived from O-amino phenyl propionic acid which was transformed in a ring on heating into a nitrogenous derivative. The new ring system so formed was named cinnoline (I).

Cinnoline is an aromatic heterocyclic compound with the molecular formula C₈H₆N₂. It is isomeric with phthalazine and its alternative name is benzopyridazine. Cinnolines are cinnoline derivatives. A classic organic reaction for synthesizing cinnoline, is a Widman-Stoermer synthesis¹⁰. A ring closing reaction of an α-vinyl aniline with hydrochloric acid and sodium nitrite.

Cinnoline is a pale yellow solid of geranium like odour which is soluble in water. Busch and Rast¹¹ state that cinnoline is a strong base, but this statement was clearly based on qualitative study and recent quantitative work has established that the base is actually fairly weak. (Pka = 2.51 at 21-22ºC in 50% aqueous alcohol¹² 2.70 at 20ºC in water¹³). It melts at 37-38ºC¹⁴ cinnoline is distinctly toxic.

Derivatives of cinnoline and their benzo and heterocyclic analogs exhibit biological activity in various areas including antihyper tensive, antithrombotic, antitumour, antisecretary and bactericidal activities^15-18_. 4-Amino cinnolines became of recent importance due to their antibacterial, antihistamine and insecticidal properties¹⁹.

b-Dimethyl amino ethyl cinnoline 4-carboxylate was inactive as an antifungal agent, in the inhibition of cholesterol biosynthesis and in tryptamine potentiation in rats²⁰_.

The dihydropyrazoles are called pyrazolines and their possible tautomeric structures are 1-pyrazoline (II), 2-pyrazoline (III) and 1,3-pyrazoline (IV).

2- pyrazoline more stable, it can be prepared as indicated and is a colourless liquid b.p. 140ºC. In contrast to pyrazole, which is so stable to acid and bases, pyrazoline is decomposed by hot water.

Pyrazole (V) refers both to the class of simple aromatic ring organic compounds of the heterocyclic series characterized by a 5-membered ring structure composed of the three carbon atoms and two nitrogen atoms in adjacent positions and to the unsubstituted parent compound. Pyrazole is a tautomeric substance. This cannot be demonstrated in pyrazole itself, but may be shown as follows²¹

Pyrazole belongs to 1,2-diazole family, its molecular formula is C₃H₄N₂ melting point 66-70ºC and boiling point is 168-188ºC.

Knorr first described the correctly formulated pyrazoles in 1883, introducing the name to describe the relationship to pyrrole. They discovered the antipyretic (temperature reducing action) of pyrazole derivatives in man.

The dimensions of a planner molecule are illustrated in figure (I) with the bond lengths being compared with those for pyrrole and pyridine .

Figure I

Pyrazole exhibits aromatic character with properties resembling both pyridine and pyrrole.

The hydrazones of α b unsaturated aldehydes and ketones are isomerised to pyrazoline (VII), when warmed with acetic acid to hydrogen chloride in ethanol.

Pyrazolines (VIII) are often formed by the direct action hydrazine or its primary derivatives on the saturated carbonyl compounds or on progenitors of these, such as mannich bases pyrazolines acids or esters are similarly obtained.

Pyrazolines are prominent nitrogen containing heterocyclic compounds and therefore various procedures have been worked out for their synthesis.Pyrazolines and its derivatives have not been found in nature. The addition of aliphatic diazo compounds to olefins leads to pyrazolines^. Pyrazoline derivatives found to have potential antipyretic analgesic,antiinflammatory, cytotoxic activity, inhibitory activity of platelet aggregation,herbicide activity, pyrazoline interest extended to dyes and dye couplers. pyrazolines are important nitrogen containing heterocyclic compounds and some of them possess valuable biological activities, e.g. central nervous system,³⁶ Immunosuppressive and antimicrobial activities. 2- pyrazolines are most popular and frequently studied pyrazoline isomers.

MATERIALS AND METHODS:

Step (i) Synthesis of phenyl hydrazono acetyl acetone :

Benzene diazonium chloride was prepared by dissolving sodium nitrile (0.1 mol) in 25 ml of water adding it dropewise to a solution of aniline in 1NHCl (200 ml) at 0ºC while stirring. The temperature was maintained at 0ºC for another 10 minutes under stirring. Benzene diazonium chloride solution obtained was then added to a well stirred solution of ethanol (30 ml), water (500 ml) and acetyl acetone (0.1 mol) at 0ºC with stirring. Sodium acetate was then added to keep the mixture alkaline to litimus after 3 hr stirring at 0ºC, the crude product was filtered, washed with water and air dried. Recrystallization from ethanol afforded yellow needles of purified phenyl hydrazono acetyl acetone.

Step (ii) Synthesis of 1-(3,4-dihydro-4-methyl cinnolin-3-yl) ethanone:

Phenyl hydrazono acetyl acetone (0.05 mol) was added to polyphosphoric acid (16 g) in small lots over 2 hr. while maintaining the temperature between 60-65ºC. Once the addition was over, the same temperature was maintained for an additional 4 hr. Reaction was maintained by TLC. After completion of the reaction, chilled water (200 ml) was added carefully to decompose the black residue at 0-5ºC.

The product was then extracted with ethyl acetate.The layer of Ethyl acetate was then treated with charcoal and concentrated to get the crude product as a brownish black residue. After purification by recrystallisation from methanol, the product was yielded as light yellow crystals.

Step (iii) Synthesis of 3-(aryl substituted)-1-(4-methyl cinnoline-3-yl) prop-2-en-1-one:

To a solution of 1-(3,4-dihydro-4methyl cinnolin-3-yl) ethanone (0.01 mol) in ethanol (30 ml) was added a solution of substituted aldehyde in ethanol , stirred and later NaOH solution (40%) 10 ml was added keeping at room temperature for 12 hrs. Then it is rendered acidic with dilute HCl and poured over crushed ice. The solid thus obtained is washed with water and recrystallized from absolute alcohol and its purity checked by T.L.C. The yield, melting points, elemental analysis and spectral data have been reported in tables.

Step (iv) Synthesis of 3-(4,5-dihydro-5-(aryl substituted)-1H-pyrazole-3-yl)-4-methyl cinnoline:

A mixture of synthesized Synthesis of 3-(aryl substituted)-1-(4-methyl cinnoline-3-yl) prop-2-en-1-one (0.01 mol) in acetic acid and hydrazine hydrate (0.01 mol) refluxed 10 hrs. The contents are poured into crushed on water bath ice and product was isolated crystallized from ethanol. The purity of compound has been checked by TLC. The yield, melting points, elemental analysis and spectral data have been given in tables.

Table;-1 Physical data of new synthesized cinnoline and pyrazoline derivatives:

Compound 1
Name	1-(4-methyl cinnolin-3-yl)-3-(4-nitrophenyl) prop-2-en-1-one
M.F.	C₁₈H₁₃N₃O₃
M.wt.	319.31
M.P.(⁰C)	82
Yield (%)	66%
Elemental analysis	C%		N%		H%
	Found	Calc.	Found	Calc.	Found	Calc.
	67.69	67.71	13.15	13.16	4.08	4.10

Compound 2
Name	3-(4-dimethyl amino) phenyl)-1-(4-methyl cinnoline-3-yl) prop-2-en-1-one
M.F.	C₂₀H₁₈N₃O
M.wt.	317.88
M.P.(⁰C)	79
Yield (%)	68
Elemental analysis	C%		N%		H%
	Found	Calc.	Found	Calc.	Found	Calc.
	70.67	70.69	13.23	13.24	6.01	6.03

Table;-2 H¹NMR spectral data of new synthesized cinnoline, pyrazoline derivatives :

S. No.	Chemical shift in d ppm	Multiplicity	Integral	Relative no. of protons	Inference
1.	7.46	Unsym. multiplet	5.504	4	Cinnoline benzene ring
2.	6.07	Unsym. multiplet	4.128	3	Bromo substituted benzene ring
3.	4.02	Doublet	1.364	1	CH=CH
4.	4.24	Doublet	1.376	1	CH=CH
5.	3.04	Singlet	4.092	3	CH₃

Table;-3 Infrared spectral data of new synthesized cinnoline, pyrazoline derivatives :

Group	Stretch mode (Vibrations)	Frequency (cm^-1)
Aromatic ring	Ar-H str.	2902.96
	C-H str.	2821.55
	C=C str.	1602.9
	C=C str.	1654.98
	C=O str.	1537.32
	C-H out of plane bending	813.99
	C-H bending in plane	1373.36
Cinnoline ring	N=N str.	1550.82
Cinnoline ring	C-N str.	1307.78

Table 4 : Antibacterial activity of the synthesized heterocyclic compounds (cinnolines , pyrazolines ,against various bacteria at two different concentrations (in ppm)

Compound	*B. subtilis*		*E. coli*		*K. pneumoniae*		*S. aureus*
Compound	50	100	50	100	50	100	50	100
DKI 1	-	-	+	++	-	+	+	++
DKI 2	-	+	+	+	+	++	-	+
DKI 3	+++	+++	++	+++	++	+++	++	++
DKI 4	++	+++	+	++	+	++	+	++
DKI 5	+++	+++	++	+++	++	+++	++	++
DKI 6	+	++	+	++	++	++	+	++
DKI 7	-	+	+	++	++	++	+	++
DKI 8	-	+	-	-	+	++	+	++
DKI 9	+	++	+	++	+	++	-	+
DKI 10	++	++	-	+	+	++	+	+
DKI 11	+	++	+	++	-	+	-	+
DKI 12	+	++	+	+	+	++	+	++
DKI 13	-	+	+	++	-	+	+	++
DKI 14	-	+	+	++	-	-	+	++
DKI 15	+++	+++	++	+++	++	+++	+	+++
DKI 16	++	+++	++	+++	++	+++	+	++
Std.	+++	++++	+++	++++	+++	+++	+++	++++

Table:-5 Antifungal activity of the compounds against synthesized heterocyclic compounds cinnolines , pyrazolines , various fungi at two different concentrations (in ppm)

Compound	*A. flavus*		*A. niger*		*F. oxisparum*		*T. viridae*
Compound	100	500	100	500	100	500	100	500
DKI 1	+++	++++	++	+++	++	+++	+	++
DKI 2	+++	+++	++	+++	++	+++	++	++
DKI 3	-	+	+	+	+	++	+	++
DKI 4	+	++	++	++	+	++	-	+
DKI 5	+	++	+	++	+	++	+	++
DKI 6	-	-	+	++	+	+	-	+
DKI 7	-	+	++	++	+	++	+	++
DKI 8	+	++	-	+	+	++	-	-
DKI 9	+++	+++	++	+++	++	+++	++	++
DKI 10	-	+	+	++	+	++	-	+++
DKI 11	+	+++	+	++	+	++	+	++
DKI 12	+	++	+	++	+	+	-	+
DKI 13	+	++	+	++	-	+	+	+
DKI 14	+++	++++	+++	+++	++	+++	+	++
DKI 15	-	+	++	++	+	++	+	++
DKI 16	+	++	++	+++	+	++	-	+
Std.	+++	++++	+++	++++	+++	+++	+++	++++

std: Griseofulvin; inhibition diameter in mm

(-) 4; (+) 5 - 9; (++) 09-11; (+++) 09-10; (++++) 12-19

CONCLUSION:

Aniline on treatment with sodium nitrite (20 ml water) at 0ºC gives benzene diazonium chloride. In the step Griess diazotization reaction takes place. Benzene diazonium chloride on treatment with acetyl acetone gives phenyl hydrazono acetyl acetone. That phenyl hydrazono acetyl acetone formed a, b unsaturated compound chalcone with substituted aldehyde in the presence of NaOH. The chalcone gives pyrazoline ring on treatment of hydrazine hydrate in presence of glacial acetic acid. All the synthesized cinnoline and cinnoline based pyrazoline derivatives were characterized by IR, ¹HNMR and elemental analysis. The antimicrobial, insecticidal and anthelmintic activity studies of synthesized compounds have shown moderate to good activity reported in respectively.

ACKNOWLEDGEMENT:

The authors are thankful to SAIF, CDRI Lucknow providing the NMR spectra and analytical data of the compounds. The authors are thankful to Prof. P.S. Parte, Department of Zoology GDC Sausar, Prof. P. Mehta Department of Botany Dr. H. S. Gour University for their kind help in antimicrobial, antifungal activity and Prof. O. P. Shrivastava Head, Department of Chemistry, Dr. H. S. Gour University, Sagar for providing IR spectral data and laboratory facilities.

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Received on 06.07.2013 Modified on 22.07.2013

Asian J. Research Chem. 6(9): September 2013; Page 832-838