A compound of general formula I wherein R 1 is selected from hydrogen and halogen; R 2 is halogen; each R 3, R 15, and R 16 is independently selected from hydrogen, OR a, OCOR a, OCOOR a, and =O, with the proviso that when a =O group exists the hydrogen of the C atom to which the =O is attached is absent; each R 4, R 5, R 6, R 7, R 11, R 12, and R 14 is independently selected from hydrogen, OR a, OCOR a, and OCOOR a; each R 8, R 9, and R 17 is independently selected from hydrogen, OR a, OCOR a, OCOOR a, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, and substituted or unsubstituted C 2 -C 12 alkynyl; R 10 is selected from hydrogen, OR b, OCOR a, OCOOR a, and =O, with the proviso that when a =O group exists the hydrogen of the C atom to which the =O is attached is absent; R 13 is selected from hydrogen, COR a, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, and substituted or unsubstituted C 2 -C 12 alkynyl; each R a is independently selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted heterocyclic group; each R b is independently selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclic group, and substituted or unsubstituted sugar; and the ------- line represents an additional bond, an epoxy group, or is absent; or a pharmaceutically acceptable salt or stereoisomer thereof. R 1 is selected from hydrogen and halogen; R 2 is halogen; each R 3, R 15, and R 16 is independently selected from hydrogen, OR a, OCOR a, OCOOR a, and =O, with the proviso that when a =O group exists the hydrogen of the C atom to which the =O is attached is absent; each R 4, R 5, R 6, R 7, R 11, R 12, and R 14 is independently selected from hydrogen, OR a, OCOR a, and OCOOR a; each R 8, R 9, and R 17 is independently selected from hydrogen, OR a, OCOR a, OCOOR a, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, and substituted or unsubstituted C 2 -C 12 alkynyl; R 10 is selected from hydrogen, OR b, OCOR a, OCOOR a, and =O, with the proviso that when a =O group exists the hydrogen of the C atom to which the =O is attached is absent; R 13 is selected from hydrogen, COR a, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, and substituted or unsubstituted C 2 -C 12 alkynyl; each R a is independently selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted heterocyclic group; each R b is independently selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclic group, and substituted or unsubstituted sugar; and the ------- line represents an additional bond, an epoxy group, or is absent; or a pharmaceutically acceptable salt or stereoisomer thereof.