Pteridine-2,4-Diamine Derivatives as Radical Scavengers and Inhibitors of Lipoxygenase that can Possess Anti-Inflammatory Properties

Figures & data

Figure 1.  Pterin and pteridine derivatives of biological or medicinal importance.

Figure 2.  Synthesis of pteridines (5).

Reagents and conditions: (A) Na, ethanol, reflux. 2 h; (B) methyl iodide, ethanol, reflux 1.5 h; (C) NaNO₂ aqueous acetic acid, 0°C, 2 h then 4°C, 16 h; (D) 1-methylpiperazine ethanol, reflux 0.75 h then add water and reflux 0.75 h; (E) sodium dithionite then aqueous 40% glyoxal (5a) or butane-2,3-dione (5b, or benzil [5c]), reflux 8 h, 18 h and 24 h, respectively.

Figure 3.  Synthesis of 5,6,7,8-tetrahydropteridines (10).

Reagents and conditions: (A) 1-methylpiperazine, reflux, 18 h; (B) NaNO₂ aqueous acetic acid, 0°C, 3 h; (C) sodium dithionite then aqueous 40% glyoxal, reflux 7 h; (D) NaHB(OAc)₃ (9 eq for 10a and 1 eq for 10b), acetic acid 48 h, 20°C.

Figure 4.  Synthesis of pteridine 13.

Reagents and conditions: (A) 3-hydroxypiperazine, reflux 5 h; (B) NaNO₂ aqueous acetic acid 0°C, 3 h; (C) sodium dithionite then aqueous 40% glyoxal, reflux 6 h.

Figure 5.  Synthesis of pteridines 18 and 20.

Reagents and conditions: (A) R¹CH₂NH₂ diglyme, reflux, 5 h; (B) NaNO₂ aqueous acetic acid, 0°C, 2 h then 4°C, 16 h; (C) 1-methylpiperazine or 4-methyl-1,4-diazepane, ethanol, reflux, 2 h then add water and reflux 1 h; (D) sodium dithionite then aqueous 40% glyoxal or butane-2.3-dione, reflux.

Figure 6.  Synthesis of pteridine analogs 21, 22 and 23.

Reagents and conditions: (A) H₂, 10% Pd on C, ethanol; then NaNO₂, glacial acetic acid, 90°C, 2 h; (B) sodium thiosulfate pentahydrate, aq. 20% acetic acid 90°C, 1.5 h; (C) lead tetraacetate, acetic acid, 20°C, 4 h.

Figure 7.  Docking pose of pteridine 18d (depicted in turquoise) bound to soybean lipoxygenase (LOX-1) derived by modification of PDB code: 3PZW.

Energy minimizations were carried out using the AMBER99SB-ILDN force field [41] with GROMACS as the molecular simulation toolkit [42]. AutoDock Vina (1.1.2) [41] was used for docking. Iron is rendered as a brown sphere. Prepared using PyMOL, this figure represents the preferred pose according to scoring function.

Table 1.  Inhibition of soybean lipoxygenase by substituted pteridines. 

Entry	Compound	Structure	cLogP^43	Lipoxygenase inhibitory activity (IC50 [μM] or % at 100 μM)
1	5a		0.14	37.5 ± 0.1%
2	5b		1.08	100 ± 0.3
3	5c		3.73	22.5 ± 0.1%
4	9		0.75	5.0 ± 0.1
5	10a		3.25	5.0 ± 0.1
6	10b		3.99	55 ± 0.2
7	13		-0.16	60 ± 0.3
8	18a		2.42	31.5 ± 0.2%
9	18b		2.22	40 ± 0.2%
10	18c		3.07	22.5 ± 0.2%
11	18d		0.92	0.10 ± 0.01
12	18e		1.59	24 ± 0.3%
13	18f		2.06	55 ± 0.8
14	18g		3.01	88.5 ± 1.2
15	20a		2.59	43 ± 0.7
16	20b		2.05	62.5 ± 0.5
17	22		1.88	80 ± 2.1
18	23		3.57	19.5 ± 0.1%
19	24		3.77	74 ± 3.5
20	NDGA		3.92	1.08 ± 0.34^40

NDGA: Nordihydroguaiaretic acid.

Table 2.  Reducing ability in 2,2-diphenyl-1-picrylhydrazl assay, scavenging activity of hydroxyl radicals, and in vitro antilipid peroxidation activity of substituted pteridines.

Compound	RA (%) 100 μM		Hydroxyl radicals scavenged (%)^†	AAPH IC50 (μM)
	20 min	60 min
5a	15	14	98	41 ± 1.1
5b	0	13	94	40 ± 0.8
5c	10	6	100	0.50 ± 0.03
9	8	14	96	0.73 ± 0.2
10a	79	81	96	15 ± 0.2
10b	98	97	98	10 ± 0.43
13	6	13	95	0.33 ± 0.01
18a	2	7	91	22 ± 0.8
18b	13	20	90	21 ± 0.9
18c	11	18	97	10 ± 0.1
18d	10	11	95	32.5 ± 1.0
18e	10	17	94	0.33 ± 0.03
18f	6	4	96	100 ± 1.5
18g	12	12	100	0.10 ± 0.01
20a	4	11	92	20 ± 0.5
20b	15	19	94	41 ± 0.3
21	4	6	94	0.29 ± 0.02
22	7	10	96	0.60 ± 0.05
23	16	18	94	0.32 ± 0.02
NDGA	81	83	–	–
Trolox	–	–	73	55.5

^†Pteridine derivatives were present at 100 µM.

AAPH: Antilipid peroxidation; NDGA: Nordihydroguaiaretic acid; RA: Reducing ability.

Table 3.  In vivo colitis studies^†.

Compound	Change in body weight (%)	Score (levels 0–5)
Vehicle (control)	4.5	No activity
Vehicle + acetic acid	-6.6	Diffuse exfoliated mucosa, multiple erosion and ulcers (4–5)
Vehicle + 5a	-1.1	One rat presented normal appearance (0); the rest exhibited hyperemia and petechial bleeding (1–2)
Vehicle + 18a	-4.2	One rat exhibited hyperemia (1); the rest presented petechial bleeding (patchy to diffuse) (2–3)
Vehicle + 18d	-7	One rat exhibited patchy petechial bleeding (2), and another diffuse petechial bleeding (3); the rest presented partial exfoliated mucosa or single erosion or ulcer
Vehicle + 18f	-10.7	All rats exhibited partial to diffuse exfoliated mucosa or single/multiple erosion or ulceration (4–5)

^† In each case there were two groups, each of three rats.

Table 4.  Inhibition of carrageenin-induced rat paw edema.

Compound	Reduction of rat paw edema after 1 h (%)
18f	41^†
Indomethacin	25^†

^†Mean of two experiments.

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