wherein

R¹ is independently —H, —OH, —O—C(O)—R⁸ or —F;

R² is independently —H, —OH, —O—C(O)—R⁸ or —F;

R³ is —OH, or —O—C(O)—R⁸;

R⁴ is —H, —OH, —O—C(O)—R⁸ or —(C₁-C₈)alkyl;

wherein R³ and R⁴ can be in the form of a carbonyl oxygen (═O);

R⁵ is —H, —OH, —O—C(O)—R⁸, —(C₁-C₈)alkyl, —O—(C₁-C₈)alkyl, —NH₂ or —NHR⁸

wherein R⁴ and R⁵ can form a 3-6 membered cycloalkyl ring;

R⁶ is —H, —(C₁-C₈)alkyl, —C(H)═CH₂, —C(H)═CH(C₁-C₈)alkyl), —C(H)═C(C₁-C₈)alkyl)(C₁-C₈)alkyl), —C(H)═C═CH₂, —C(H)═C═C(C₁-C₈)alkyl)H, —CH₂C═CH, —OH or —O(C₁-C₈)alkyl;

R⁷ is —H, —OH, —OCH₃, —SH or —Cl;

R⁸ is independently —(C₁-C₈)alkyl, aryl, —(CH₂)_n(aryl), heteroaryl or —(CH₂)_n(heteroaryl);

n is an integer 1, 2, 3, 4 or 5;

wherein at least one R⁴ or R⁵ is not —H;

wherein each alkyl, cycloalkyl, aryl and heteroaryl are independently optionally substituted by one or more of CN, NO₂, halogen, (C₁-C₃)alkyl, (C₁-C₃)haloalkyl, (C₁-C₃)cycloalkyl, aryl, heteroaryl, OH, alkenyl, alkynyl, O—(C₁-C₃)alkyl, O—C(O)—R⁹, O-(alkylene)aryl, O-(alkylene)heteroaryl, C(O)R⁹, S(C₁-C₈)alkyl, S(O)(C₁-C₈)alkyl, SO₂(C₁-C₈)alkyl, C(O)OR⁹, C(O)NR⁹R⁹, C(O)NR⁹SO₂(C₁-C₈)alkyl, NR⁹R⁹, NR⁹(CO)OR⁹, NH(CO)R⁹, NH(SO₂)(C₁-C₈)alkyl or NH(SO₂)NR⁹R⁹, and R⁹ is independently —H, —OH, —(C₁-C₈)alkyl, cycloalkyl, heterocyclyl; or the two R⁹'s of C(O)NR⁹R⁹ or NR⁹R⁹ combine together with the nitrogen atom to form a heterocycle;

or a stereoisomer, a tautomer, or a pharmaceutically acceptable salt thereof.