The present invention provides generally a compound having the following general formula (1): wherein R1 and R2 are independently the same or different and are hydrogen, an alkyl group, an alkenyl group, a benzyl group, an alkynyl group, an alkoxyl group, an aryloxy group, an acyloxy group, —OC(O)ORd, wherein Rd is an alkyl group, a carbamoyloxy group, a halogen, a hydroxyl group, a nitro group, a cyano group, an azido group, a formyl group, a hydrazino group, an acyl group, an amino group, —SRc, wherein, Rc is hydrogen, an acyl group, an alkyl group, or an aryl group, or R1 and R2 together form a group of the formula —O(CH2)nO— wherein n represents the integer 1 or 2; R3 is H, F, a halogen atom, a nitro group, an amino group, a hydroxyl group, or a cyano group; or R2 and R3 together form a group of the formula —O(CH2)nO— wherein n represents the integer 1 or 2; R4 is H, F, a C1-3 alkyl group, a C2-3 alkenyl group, a C2-3 alkynyl group, or a C1-3 alkoxyl group; R5 is a C1-10 alkyl group, or a propargyl group; and R6, R7 and R8 are independently a C1-10 alkyl group, a C2-10 alkenyl group, a C2-10 alkynyl group, an aryl group or a —(CH2)NR9 group, wherein N is an integer within the range of 1 through 10 and R9 is a hydroxyl group, alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group or a nitro group; and pharmaceutically acceptable salts thereof.