A compound of Formula (A) or (B): ** (See formula) ** or a pharmaceutically acceptable salt thereof, wherein: each case of R1 and R4 is independently selected from the group consisting of hydrogen, carbonyl , silyl, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl and optionally substituted heteroaryl; each case of R2 and R3 is independently selected from the group consisting of hydrogen, halogen, -OH, substituted hydroxyl, -SH, substituted thiol, -NH2, substituted amino, - CN, -NO2, carbonyl, silyl, sulfinyl, sulfonyl, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl and optionally substituted heteroaryl; or R2 and R3 are linked to form an optionally substituted carbocyclyl group or optionally substituted heterocyclyl; R5 is hydrogen; R6 is selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl and optionally substituted heteroaryl; R7 is selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl and optionally substituted heteroaryl; R12 is selected from the group consisting of hydrogen, carbonyl, silyl, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl and optionally substituted heteroaryl; R13 is selected from the group consisting of halogen, -OH, substituted hydroxyl,