Synthesis and bioactivities evaluation of oleanolic acid oxime ester derivatives as α-glucosidase and α-amylase inhibitors

Figures & data

Scheme 1. Synthesis of oleanolic acid oxime ester derivatives (3a–3t). Reagents and conditions: (a) Jones reagent, acetone, 0 °C; (b) NH₂OH·HCl (1.0 eq.), EtOH, NaOAc (2.0 eq.), rt, 1 h; (c) cinnamoyl chlorides and benzoyl chlorides (2.0 eq.), pyridine, DCM, 0 °C ∼ rt, overnight.

Table 1. Inhibition of all the synthesised OA derivatives against α-glucosidase and α-amylase.

Compounds	R	α-Glucosidase inhibition (IC50:μM)	α-Amylase inhibition (IC50:μM)
3a		0.35 ± 0.06^a	7.86 ± 1.24^a
3b		0.68 ± 0.03^a	15.26 ± 1.41^a
3c		0.89 ± 0.07^a	25.37 ± 1.17^a
3d		1.45 ± 0.12^a	17.47 ± 1.52^a
3e		0.95 ± 0.06^a	5.64 ± 1.29^a
3f		1.28 ± 0.03^a	3.80 ± 0.65^a
3g		3.13 ± 0.13^a	12.57 ± 2.37^a
3h		1.36 ± 0.03^a	18.29 ± 1.92^a
3i		0.71 ± 0.02^a	17.87 ± 1.21^a
3j		0.82 ± 0.09^a	70.81 ± 2.31^a
3k		0.67 ± 0.04^a	25.57 ± 1.66^a
3l		0.99 ± 0.05^a	55.30 ± 2.39^a
3m		1.10 ± 0.10^a	35.47 ± 2.41^a
3n		1.96 ± 0.25^a	70.21 ± 2.53^a
3o		1.74 ± 0.14^a	26.32 ± 1.61^a
3p		1.81 ± 0.05^a	15.93 ± 1.75^a
3q		3.43 ± 0.17 ^a	33.61 ± 1.93^a
3r		1.41 ± 0.12^a	70.72 ± 1.25^a
3s		1.37 ± 0.06^a	18.68 ± 1.29^a
3t		0.91 ± 0.04^a	152.36 ± 4.24^a
OA		4.09 ± 0.11^b	94.10 ± 1.72^b
Acarbose		665.56 ± 13.92^c	100.01 ± 2.73^c

Values are the mean ± SD. Mean values in the same column having different letters are significantly different (p < 0.05).

Figure 1. Inhibition kinetics of 3a on α-glucosidase. (a) The plots of enzymatic reaction rate vs α-glucosidase concentration with or without the presence of 3a; (b) Lineweaver–Burk plots of enzymatic reaction rate versus substrate concentration with or without the presence of 3a (3a concentration: black line, 0 μM; red line, 0.25 μM; blue line, 0.45 μM; pink line, 0.5 μM).

Figure 2. The molecular docking of analogue 3a with α-glucosidase (homology mode): (a) 3a in the electrostatics active pocket; (b) 3a in the active pocket; (c) 3D view of 3a with α-glucosidase; (d) 2D view of 3a with α-glucosidase.

Table 2. The physicochemical properties of compounds 3a and 3f.

	Molecular formula	Molecular weight	Rotatable bonds	H-bond acceptoer atoms	H-bond donnor atoms	Polar surface area (Å^2)	LogPo/w	Water solubility
3a	C39H53NO4	599.84	5	5	1	75.96	7.82	Poorly soluble
3f	C39H52BrNO4	678.74	5	5	1	75.96	8.49	Insoluble

Figure 3. Inhibition kinetics of 3f against α-glucosidase. (a) The plots of enzymatic reaction rate vs α-glucosidase concentration with or without the presence of 3f; (b) Lineweaver–Burk plots of enzymatic reaction rate vs substrate concentration with or without the presence of 3f (3f concentration: black line, 0 μM; red line, 5 μM; blue line, 7.5 μM; pink line, 15.0 μM).

Figure 4. The molecular docking of analogue 3f and α-amylase (3BAJ): (a) 3f in the electrostatics active pocket; (b) 3f in the active pocket; (c) 3D view of 3f and α-amylase; (d) 2D view of 3f and α-amylase.

Figure 5. Cells cytotoxicity of compounds 3a and 3f against 3T3-L1 and HepG2 cells.

Figure 6. Ramachandran plot results of most reasonable homology mode.