Table 1. Tyrosinase inhibitory activities of new compounds.

Compounds	R1	R2	IC50 value (μM)
5a	H	OH	2.0
5b	OCH3	OH	>100 a
5c	H	OCH3	77.4
5d	H	H	>100 a
5e	H	CH3	39.0
5f	H	Cl	163.8
5g	H	F	8.3
6a	H	OH	10.6
6b	OCH3	OH	>100 a
6c	H	OCH3	>100 a
6d	H	H	>100 a
6e	H	CH3	>100 a
6f	H	Cl	>100 a
6g	H	F	>100 a
Cinnamic acid			209.5
4-Hydroxyl cinnamic acid			4708.5
Paeonol			121.4
Thymol			5925.0
Kojic acid			32.2

^aThe inhibitory percentage of these compounds at 100 μM is less than 40%.