Tyrosinase inhibitory components from Aloe vera and their antiviral activity

Figures & data

Figure 1. Structure of compounds 1–9 derived from A. vera.

Figure 2. Key HMBC (→) and COSY (-) correlations of compound 1.

Table 1. ¹H and ¹³C-NMR data for compound 1.

	1
	Position	δH^a^,^b	δC^a^,^c
1
2		164.0
3	6.65(s)	112.4
4		182.0
4a		117.6
5		144.9
6	6.84(s)	113.1
7		162.3
8		111.6
8a		159.5
9		98.6
10		203.7
11	2.35 (s)	23.7
1'	5.12 (d, J = 9.2 Hz)	72.6
2'	5.59 (t, J = 9.2 Hz)	74.3
3'	4.01 (m)	78.0
4'	3.45 (m)	71.9
5'	3.67 (m)	83.3
6'	3.91(m), 3.71 (m)	63.5
1"		167.4
2"	6.25 (d, J = 15.8 Hz)	118.5
3"	7.43 (d, J = 15.8 Hz)	146.3
4"		135.7
5", 9"	7.50 (m, 2H)	129.3
6", 8"	7.36 (m, 2H)	130.1
7"	7.36 (m)	131.6
5-CH3	2.75 (s)	25.0
7-OMe	3.88 (s)	57.2

^a Measured in CD₃OD.

^b 600 MH.

^c 150 MHz.

Figure 3. (A) Inhibitory activity of compound 9 on tyrosinase (IC_50: 9.8 ± 0.9 μM; kojic acid =19.5 ± 1.5 μM). (B) Relationship of the hydrolytic activity of tyrosinase with enzyme concentration at a variety of inhibitor concentration. (C) Lineweaver–Burk plot (Competitive type) and (D) Dixon plot (K_i: 5.8 ± 0.9 μM) for the inhibition of compound 9.

Table 2. Inhibition rate of isolated compounds 1–9 on tyrosinase and PMMoV.

	Inhibition rate at 100 μM on tyrosinase (%)^a	Inhibition rate at 1.5 mg/mL on PMMoV (%)^a
1	9.5 ± 9.0	31.5 ± 4.2
2	21.5 ± 7.2	21.5 ± 5.2
3	18.7 ± 3.1	45.2 ± 4.1
4	23.1 ± 1.8	34.1 ± 3.9
5	1.2 ± 2.5	7.5 ± 7.1
6	1.5 ± 2.8	17.5 ± 2.7
7	36.8 ± 3.1	37.5 ± 6.5
8	18.1 ± 0.9	15.4 ± 3.5
9	95.2 ± 0.5	18.2 ± 6.2
Positive control	92.5 ± 5.1^b	34.5 ± 3.5^c 10.5 ± 7.8^d

^a All compounds examined in a set of triplicated experiment.

^b Kojic acid.

^c Ribavirin.

^d Skim milk.

Figure 4. Docking pose of 9 at the lowest energy with enzyme indicated as ribbon (A). The green dotted line represents hydrogen-bond interactions between compound 9 and enzyme (B).

Table 3. Interaction and Autodock score on tyrosinase of 9.

Inhibitor	Residues in close contact	Hydrogen bond (Å)	Autodock score (kcal/mol)
9	His85, Phe90, Trp227, His244, Val248, Glu256, Met257, His259,Asn260, Thr261, His263, Phe264, Gly281, Ser282, Val283,Ala286, Cu401	His244(3.09), Thr261(2.99), Val283(3.08)	−7.43