The present invention provides generally a compound having the following general formula (1): wherein R.sup.1 and R.sup.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.sup.c, wherein, R.sup.c is hydrogen, an acyl group, an alkyl group, or an aryl group, or R.sup.1 and R.sup.2 together form a group of the formula --O(CH.sub.2).sub.nO-- wherein n represents the integer 1 or 2; R.sup.3 is H, F, a halogen atom, a nitro group, an amino group, a hydroxyl group, or a cyano group; or R.sup.2 and R.sup.3 together form a group of the formula --O(CH.sub.2).sub.nO-- wherein n represents the integer 1 or 2; R.sup.4 is H, F, a C.sub.1-3 alkyl group, a C.sub.2-3 alkenyl group, a C.sub.2-3 alkynyl group, or a C.sub.1-3 alkoxyl group; R.sup.5 is a C.sub.1-10 alkyl group, or a propargyl group; and R.sup.6, R.sup.7 and R.sup.8 are independently a C.sub.1-10 alkyl group, a C.sub.2-10 alkenyl group, a C.sub.2-10 alkynyl group, an aryl group or a --(CH.sub.2).sub.NR.sup.9 group, wherein N is an integer within the range of 1 through 10 and R.sup.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.