Table 1:

Tyrosinase inhibitory activities of carvacrol (1)/thymol (2) and their corresponding derivatives 3, 5, 7–13/4, 6, 14–20

Compound	Carvacrol (1) %Inhibition	Thymol (2) %Inhibition	Carvacrol IC50 (μM)	Thymol IC50 (μM)
Parent 1/2	35.7±5.4	29.4±3.7	n.d.	n.d.
Ethyl ether 3/4	57.5±2.5	28.8±5.6	n.d.	n.d.
4-Oxobutanoic acid 5/6	16.9±4.0	30.7±2.7	n.d.	n.d.
Methyl 4-oxobutanoate 7/14	31.7±6.2	45.5±2.1	n.d.	n.d.
Ethyl 4-oxobutanoate 8/15	50.9±2.1	72.0±5.5	n.d.	212.3±1.7
Propyl 4-oxobutanoate 9/16	85.6±6.6	78.8±2.4	217.9±4.3	154.0±3.7
Allyl 4-oxobutanoate 10/17	58.2±2.3	100.04±6.7	128.8±1.9	125.6±3.5
Butyl 4-oxobutanoate 11/18	82.3±2.1	100±3.9	176.5±2.8	191.4±2.4
Crotyl 4-oxobutanoate 12/19	72.8±3.3	99.3±8.0	244.1±3.6	102.3±.1.8
Benzyl 4-oxobutanoate 13/20	47.0±9.0	31.3±7.1	n.d.	n.d.

Kojic acid (IC₅₀ = 21.8±1.7 μM)

% Inhibition (500 μM); n.d. = not determined (IC₅₀ >500 μM)