Pyridothiadiazine derivatives as aldose reductase inhibitors having antioxidant activity

Figures & data

Figure 1. The polyol pathway of glucose metabolism.

Figure 2. Previously reported aldose reductase inhibitors.

Scheme 1. Reagents and conditions: (i) K₂CO₃, (ii) CH₃CN, 70 °C; (iii) BBr₃, CH₂Cl₂, 0 °C.

Scheme 2. Reagents and conditions: (i) K₂CO₃, CH₃CN, 70 °C; (ii) NaOHaq., THF, then HClaq. and (iii) K₂CO₃, thiophenol, NMP, 150 °C.

Scheme 3. Reagents and conditions: (i) K₂CO₃, CH₃CN, 70 °C; (ii) AlCl₃, CH₂Cl₂, 40 °C and (iii) NaOHaq., THF, then HCaq.

Table 1. Biological evaluation of pyridothiadiazine derivatives.

	Product
Comp. no.	R^1	R^2	ALR2 IC50 (μM)*	DPPH inhibition, n (%)^†	MDA (nmol/mgpro)^‡	MDA inhibition, n (%)^¶	MDA IC50 (μM)^§
13a	Br	4-OCH3	18.2 (0.52–20.76)	6.2	1.115 ± 0.008	2.6	–
13b	Cl	4-OCH3	7.54 (4.32–8.01)	5.9	1.125 ± 0.018	1.6	–
13c	CH3	4-OCH3	7.2 (4.79–7.98)	3.1	1.056 ± 0.017	8.4	–
3a	Br	4-OH	10.1 (7.85–13.92)	17.0	0.838 ± 0.001	29.9	–
3b	Cl	4-OH	6.4 (3.21–10.13)	93.2	0.392 ± 0.156	73.9	124.4 (74.7–153.5)
3c	CH3	4-OH	12.4 (4.85–16.54)	5.2	1.152 ± 0.034	0	–
5a	Br	2-F,5-OCH3	1.3 (1.03–1.24)	8.7	1.115 ± 0.004	2.3	–
5b	Cl	2-F,5-OCH3	1.74 (0.79–1.75)	8.6	1.012 ± 0.022	12.7	–
5c	CH3	2-F,5-OCH3	1.82 (0.71–2.12)	6.4	1.143 ± 0.021	0	–
6b	Cl	2-F,5-OH	2.86 (1.31–3.16)	17.2	1.036 ± 0.009	10.4	–
6c	CH3	2-F,5-OH	2.86 (1.58–4.31)	9.8	1.138 ± 0.053	0.3	–
8	Br	3-OCH3,5-OCH3	14.2 (4.10–17.91)	11.5	1.109 ± 0.010	3.2	–
11	Br	3-OH,5- OCH3	11.7 (6.22–14.38)	21.3	0.934 ± 007	20.4	–
12	Br	3-OH,5-OH	13.1 (5.77–12.07)	49.8	0.799 ± 0.005	38.7	–
Epalrestat			0.12 (0.08–0.13)	0	1.148 ± 0.032	0	–
Trolox				95.0	0.052 ± 0.002	98.1	–
Blank					0.127 ± 0.002
Control					1.141 ± 0.056

*IC₅₀ (95% CL) values represent the concentration of the tested compounds required to decrease enzymatic activity by 50%.

† Inhibitory effects were evaluated at a concentration of 100 μM.

‡ Blank: brain homogenate; control: brain homogenate + the oxidant system (FeCl₃ 20 μM and ascorbic acid 100 μM); the inhibitory effect was estimated at a concentration of 100 μM.

¶ The MDA inhibitory activity % was calculated using the following equation: Inhibitory effect % = [(control − test)/(control − blank)] × 100%. Blank: brain homogenate; control: brain homogenate + the oxidant system (FeCl₃ 20 μM and ascorbic acid 100 μM); test: brain homogenate + the oxidant system (FeCl₃ 20 μM and ascorbic acid 100 μM) + compound.

§ IC₅₀ (95% CL) values represent the concentration of the tested compounds required to inhibit the production of MDA by 50%.

Figure 3. Molecular docking of compound 13b (A & B) and 3b (C & D). (A & C) Docking of compounds 13b or 3b into the ALR2 active site. The protein structure is shown in ribbon and tube representation with selected residues labeled and shown in line representation; ligand 13b (or 3b) and NADPH are shown as stick models. The docked pose of 13b and 3b are shown in yellow. Hydrogen bonds are shown as green dashed lines. (B & D) Surface representation of protein active site residues in the docking of 13b or 3b into the active site of ALR2.