4,5-Dihydro-1H-pyrazole: an indispensable scaffold

Figures & data

Figure 1. Pyrazole and 4,5-dihydro-1H-pyrazole.

Figure 2. Various substitutions on pyrazoline ring.

Figure 3. Retrosynthetic approach for the synthesis of pyrazoline derivative.

Figure 4. Various N-substitutions on the pyrazoline ring.

Table 1. Structural modification on 2-pyrazolines.

				IC50 (µM)
Compound	R1	R2	R3	HCT-116	MCF-7
5A1	H	F		–	3.43
5A2				7.09	–
5B1		o-CI		6.8	12
5C1		F		–	16.5
5C2		NO2		10.3	–

Table 2. Structural modification on steroidal based 2-pyrazolines.

		IC50 (µM)
Compound	R	HT-29	HCT-15	502713	HOP-62	A-545	MCF-7	SF-295
6A		6.35	2.31	0.56	1.46	11.0	0.43	0.63
6B		11.8	23.4	44.2	50.0	48.1	ND	50.6
6C		0.44	0.53	0.32	0.50	1.42	1.60	3.79
6D		2.37	21.8	28.5	32.9	29.2	23.1	49.5
6E		0.24	0.25	37.0	50.0	32.2	17.5	30.2

Table 3. Structural modification on 3-amino based pyrazole derivatives.

			Cytotoxicity (IC50, µM)
Compound	Ring A	Ring B	K562	ECA-109	A549	SMMC-7721	PC-3
7A	3,4,5-(OCH3)3	4-OCH3	0.08 ± 0.04	12.01 ± 2.45	1.38 ± 0.94	12.07 ± 2.66	6.95 ± 0.74
7B	4-OCH3	3,4,5-OCH3	ND	25.04 ± 6.25	40.38 ± 3.21	ND	7.68 ± 5.27
7C	3,4,5-(OCH3)3	4-Cl	0.31 ± 0.16	8.00 ± 1.35	6.03 ± 2.51	13.79 ± 5.24	0.61 ± 0.53

Table 4. Structural modifications on N₁-acetyl derivative of pyrazolines and their anticancer activity against NCIH-460 cancer cell line.

Compound	R	NCIH-460 IC50 (µM)
8B1	4-MeO	>20
8B2	4-MeS	8.0 ± 0.1
8B3	4-NH2	2.6 ± 0.1
8B4	4-Me2N	1.8 ± 0.06
8B5	4-Me	1.3 ± 0.05
8B6	3-Br	0.35 ± 0.01
8B7	3-NH2	0.74 ± 0.33
8B8	3-OH	2.3 ± 0.06
8B9	3-MeO-4-OH	0.21 ± 0.005

Table 5. Antimicrobial activities of N₁-acetyl pyrazolines.

			MIC (µg/mL)
			Gram positive			Gram negative
Compound	R1	R2	B. subtilis ATCC 6633	S. aureus ATCC 6538	S. faecalis ATCC 9790	P. aerug-inosa ATCC 13525	E. coli ATCC 35218	E. cloacae ATCC 13047
9A	4-OCH3	4-F	6.25	6.25	1.562	12.5	0.39	12.5
9B	4-OCH3	4-Cl	6.25	25	6.25	25	0.78	25
9C	4-Cl	4-OCH3	12.5	>50	25	25	25	>50
9D	3,4-Cl	4-Cl	0.78	25	6.25	25	25	>50

Table 6. COX-II inhibitory activity of some N₁-substituted pyrazoline.

Compound	R	X	IC50 (µM)
10A	2-OCH2Ph	COCH3	3.20 ± 0.24
		CSNH2	Inactive at a conc. 25µM
10B	4-CH3	COCH3	6.77 ± 0.48
		CSNH2	31.85 ± 2.57

Table 7. Anti-inflammatory & antioxidant activities of 2-pyrazolines.

Anti-inflammatory activity
		% Inhibition		COX-2 enzyme inhibition assay
Compounds	Ar	COX-I	COX-II	In vitro % inhibition (100 µM)	In vivo % inhibition
Indomethacin		63.87	28.43	28.43	47.0 ± 1.1
11A		24.15	88.43	88.43	60.3 ± 4.5
11B		23.49	86.85	86.85	54.3 ± 1.1
11C		18.50	48.43	48.43	42.2 ± 11.8

Antioxidant activity
		% Radical scavenging activity
Compound	Ar			DPPH radical	SOR radical	OH radical
Ascorbic acid			91.52	51.95	88.34
11D		24.15	40.53	92.08	81.67	69.34
11E		8.85	10.15	91.74	86.26	78.64

Table 8. Anticonvulsant and antidepressant activities of N1-thiourea derivatives of pyrazoline.

Antidepressant
Compound	R	Ar	Antidepressant activity (Duration of immobility) (mean ± S.E.M.)
12A	C2H5	Phenyl	139 ± 12
12B	C3H5	2-furyl	144 ± 21.4
Anticonvulsant
			MES		scMET
Compound	R	Ar	Time (hrs)	Conc (mg/kg)	Time (hrs)	Conc (mg/kg)
12C	Phenyl	2-furyl	1/2	100 & 300	No activity
12D	2-furyl	C2H5	4	300	1/2	30,100,300

Table 9. XO inhibitory activity of N₁-acetyl pyrazolines.

Compound	Ring A	Ring B	R	XO inhibitory activity IC50 (µM)
13A			H	61.4
13B			H	41.3
13C			H	26.4
13D			R2 = –OCH3	21.3
13E			R2 = NO2	13.1
13F			–	91.4

Table 10. MAO inhibitory activity of some pyrazolines.

			MAO inhibitory activity (pIC50)
Compound	X	R	hMAO-A	hMAO-B
Clorgyline (MAO-A inhibitor)			8.35	4.21
Deprenyl (MAO-B inhibitor)			4.17	7.70
14A		OCH2Ph	6.50	6.76
14B		CH3	–	–
14C		OCH2Ph	–	6.57
14D		CH3	–	–

Table 11. Various of N₁-pyridamide pyrazoles.

Compound	R	R1
15A	2-Thiophene	p-NO2
15B	p-(CH3)N	p-Br
15C	p-Cl	p-Cl
15D	p-OCH3	p-Cl

Table 12. Antimicrobial activity of various of N₁-pyridamide pyrazoles.

	Diameter of the zone of inhibition (mm) at 10 µg/mL concentration
	Anti-bacterial activity				Anti-fungal activity
Compound	S. aureus	B. subtilis	E. coli	P. aeruginosa	C. albicans	A. niger
15A	12	16	13	16	15	14
15B	13	13	16	14	15	14
15C	14	14	15	12	16	16
15D	14	14	14	13	15	15
Streptomycin	24	21	22	22	–	–
Griseofulvin	–	–	–	–	23	22
Control (DMF)	–	–	–	–	–	–

Table 13. MIC values for antituberculer activity.

Compound	R	R1	Antituberculer activity MIC (µg/mL)
16A	2-OCH3	2,6-Dichloro phenyl-	1.66
16B	2-OCH3	3-Nitro phenyl-	–
16C	2-OCH3	3,4-Dimethoxy phenyl-	5.67
16D	2-OCH3	3,4,5-Trimethoxy phenyl-	–
16E	2-CH3	3,4,5-Trimethoxy phenyl-	–

Table 14. Anti-amoebic activity of bispyrazolines.

Compound	R	Anti-amoebic activity IC50 (µM)
17A		0.42
17B		0.62
17C		0.92
17D		1.16
Metronidazole		1.8

Table 15. In-vitro anti-amoebic activity of compounds against HM1: IMSS strain of Entamoeba histolytica and their toxicity profile.

			Anti-amoebic activity
Compound	R1	R2	IC50 (µM)	Safety Profile (SI)
18A	Cl	H	3.15	28.76
18B	Cl	OCH3	2.63	>38.02
18C	CH3	CH3	0.86	>116.27
18D	CH3	OCH3	1.08	>92.59
Metronidazole			1.80	>55.55

Table 16. Anti-HIV activity of N₁-pyridamide pyrazoles.

Compound	R	IC50 (µM)
19A	4-Dimethylaminophenyl-	5.7
19B	Furyl-	6.8
19C	4-Chlorophenyl-	>36.1
19D	2,6-Dichlorophenyl-	>13.83

Table 17. Antimalarial activity of some N₁-pyridamide pyrazoles.

					Antimalarial activity
Compound	R1	R2	R3	R4	MRC-02	RKL9
20A	Cl	H	Cl	H	0.0375 ± 0.005	0.0680 ± 0.019
20B	Br	H	H	H	0.0272 ± 0.005	0.0640 ± 0.003

Table 18. Anlgesic and anti-inflammatory activities of morpholine containing pyrazolines.

						Increase in paw volume (mL) after carageenan administration
Compound	X	R1	R2	R3	Number of writhings	2 h	3 h	4 h	24 h
Control					71 ± 3	1.49 ± 0.20	1.64 ± 0.15	1.57 ± 14	1.92 ± 0.12
Diclofenac					08 ± 2	0.18 ± 0.03	0.18 ± 0.015	0.18 ± 0.02	0.03 ± 0.01
21A	H	H	H	Cl	53 ± 4	1.52 ± 0.12	1.60 ± 0.18	1.61 ± 0.12	1.92 ± 0.18
21B		H	H	Br	15 ± 4	0.86 ± 0.15	0.52 ± 0.14	0.64 ± 0.10	0.98 ± 0.12
21C		H	H	Cl	09 ± 2	0.64 ± 0.10	0.72 ± 0.14	0.72 ± 0.12	0.86 ± 0.12
21D		H	H	Br	13 ± 3	0.87 ± 0.12	0.69 ± 0.13	0.91 ± 0.17	0.92 ± 0.16

Table 19. Structural modification of some N-substituted pyrazolines.

Compound	Ar	R	R′	R″
22A	C6H4 Br-4	H	N(CH3)2
22B	C6H4 Br-4	Cl	H	Ph
22C		–OCH3	H
22D		H	Cl	Ph
22E	C6H5	H	H

Table 20. Antibacterial activity of 22A–22E.

	Gram-positive bacteria						Gram-negative bacteria
	S. aureus			B. subtilis			E. coli			P. aeruginosa
Compound	1.25	2.5	5.0	1.25	2.5	5.0	1.25	2.5	5.0	1.25	2.5	5.0
22A	+	+	++	+	++	++	+	+	++	0	0	+
22B	0	0	+	0	0	+	+	+	+	0	0	0
22C	0	+	+	0	+	+	0	+	+	0	0	0
22D	0	0	0	0	0	0	0	+	+	0	0	0
22E	+	+	++	+	++	++	+	++	++	0	0	+

Chloramphenicol is the standard antibacterial control.

Inhibition values = 0.1–0.5 cm beyond control = +; Inhibition values = 0.6–1.0 cm beyond control = ++; and 0 = not detected.

Table 21. Antifungal activity of 22A and 22B.

	A. fumigatus			P. italicum			S. racemosun			C. albicans
Compound	1.25	2.5	5.0	1.25	2.5	5.0	1.25	2.5	5.0	1.25	2.5	5.0
22A	+	+	++	+	+	0	+	++	++	0	+	+
22B	0	0	0	0	+	+	0	0	0	0	+	+

Table 22. Antimicrobial activity of steroidal pyrazolines.

Compound	MIC (Antibacterial)
2′-(2″,4″-dinitrophenyl)-5a-cholestano [5,7-c d] pyrazolines	E. coli	C. xerosis	S. epidermidis
	3.125	0.781	0.195
	MIC (Antifungal)
	M. azygosporus	C. purpurea	A. niger
	3.125	6.250	1.562

Table 23. Antimicrobial activity of 23A–23D.

Antibacterial activity (mm)
		Gram-positive bacteria			Gram-negative bacteria
Compound	X	B. subtilis	M. luteus	S. aureus	E. coli	K. pneumoniae
23A	4-F	9	7	6	9	7
23B	4-Br	8	8	7	7	7
23C	4-Cl	8	7	–	10	7
23D	4-CH3	6	–	–	12	7
Ampicillin		20	18	18	18	12

Antifungal activity (mm)
Compound	X	A. niger	T. viride
23A	2-Cl	–	10
23B	3-Cl	–	10
23C	4-F	9	7
Miconazole		14	16

Table 24. Antimicrobial activity of 24A1–24B3.

			Halo zone test (unit, mm)
			Microorganisms
Compound	Ar	X	A. hydrophila	Y. enterocolitica	L. monocytogenes	S. aureus
Gentamycin			21	–	–	17
24A1			21.5	24.4	21.3	22.8
24B1			25.3	18.6	20.8	24.5
24A2			22.3	21.4	24.3	22.8
24B2			21.7	25.2	19.4	23.6
24A3			20.5	22.4	24.3	22.8
24B3			21.7	18.4	21.2	19.4

Table 25. Anti-inflammatory activity of benzene sulphonamide derivative of 2-pyrazolines.

	Carrageenan-induced rat paw edema assay
	3 h		5 h
Compound	Increase in the paw volume (ml)	% Inhibition	Increase in the paw volume (ml)	% Inhibition
Celecoxib	0.12 ± 0.0041	79.59	0.09 ± 0.0031	82
	0.12 ± 0.004	80	0.09 ± 0.003	81.82
	0.125 ± 0.005	78.95	0.125 ± 0.004	75

Table 26. Anti-inflammatory activity of coumarin based 2-pyrazolines.

		Anti-inflammatory activity
		In vitro % inhibition
Compound	Ar	2 h	4 h	In vivo % inhibition after treatment
25A	2,4-Cl2-C6H3	56.7 ± 0.030	67.5 ± 0.024	45.4 ± 1.63
25B	4-F-C6H4	44.9 ± 0.023	66.7 ± 0.011	40.5 ± 1.80
25C	4-Cl-C6H4	39.2 ± 0.026	64.7 ± 0.021	39.1 ± 0.81
25D	3-OMe-C6H4	38.3 ± 0.030	61.5 ± 0.013	20.9 ± 1.25
Diclofenac		63.7 ± 0.017	78.7 ± 0.013	53.0 ± 1.92

Table 27. Antimicrobial activity of N₁-phenyl substituted pyrazolines.

Anti-tubercular activity (% reduction in rlu)
Compound	R	X	50 µg/ml						100 µg/ml
26a	SO2CH3	–	1.70						50.71
26b	SCH3	–	0.00						17.65
Antibacterial activity (mic in µm)
Compound	R	X		E. coli	P. vulgaris		E. aerogenes		S. aureus	S. typhii		B. subtilis
26a	SO2CH3	–		0.166	0.332		0.332		0.664	0.332		0.332
26c	SCH3	Cl		0.152	0.304		0.304		0.608	0.304		0.304
26d	SCH3	Br		0.148	0.295		0.295		0.591	0.295		0.295
Antifungal activity (% inhibition at 2mg/ml concentration)
Compound	R	X		F. proliferatum		C. tropicalis		A. flavus			A. niger
26a	SO2CH3	–		97.61 ± 0.47		30.64 ± 0.30		65.85 ± 1.82			47.20 ± 5.03
26c	SCH3	Cl		88.26 ± 0.90		95.58 ± 1.05		88.44 ± 1.92			97.54 ± 0.07
26e	SCH3	F		98.71 ± 0.16		97.41 ± 1.40		94.82 ± 0.16			97.28 ± 1.31

Table 28. In-vitro anticancer activity of compound NSC 748326.

Panel	Cancer cell lines	GI50 (µM)
Leukemia	CCRF-CEM	2.23
	RPMI-8226	2.76
Renal	CAKI-1	3.6
	UO-31	2.2
Prostate	PC-3	6.27
	DU-145	33.1
Colon	HCT-116	3.94
	HCT-15	4.1
Breast	MCF7	2.41
	MDA-MB-468	5.25