the present invention provides generally a compound having the following general formula : wherein r 1 and r 2 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 , a carbonyloxy 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 , — sr c , wherein , r c is hydrogen , an acyl group , an alkyl group , or an aryl group , or r 1 and r 2 together form a group of the formula — o n o — wherein n represents the integer 1 or 2 ; r 3 is h , f , a halogen atom , a nitro group , an amino group , a hydroxyl group , or a cyano group ; or r 2 and r 3 together form a group of the formula — o n o — wherein n represents the integer 1 or 2 ; r 4 is h , f , a c 1 - 3 alkyl group , a c 2 - 3 alkenyl group , a c 2 - 3 alkynyl group , or a c 1 - 3 alkoxyl group ; r 5 is a c 1 - 10 alkyl group , or a propargyl group ; and r 6 , r 7 and r 8 are independently a c 1 - 10 alkyl group , a c 2 - 10 alkenyl group , a c 2 - 10 alkynyl group , an aryl group or a — n r 9 group , wherein n is an integer within the range of 1 through 10 and r 9 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 .