A compound which is a nitroso derivative of formula VI or a pharmaceutically acceptable salt thereof: wherein each R 11a, R 11b,R 12a, R 12b, R 13a, R 13b, R 14a and R 14b is H; and wherein D is selected from (i) the group consisting of C 1 -C 8 alkyl-C -, perhaloalkyl-C -, C 2 -C 10 alkenyl-C -, C 2 -C 10 alkynyl-C -, C 6 -C 14 aryl-C -, heteroaryl-C - with a 5- or 6-membered ring, heterocyclyl-C - with a 5- or 6-membered ring and -P (OC 1 -C 8 alkyl) 2, wherein each alkyl, alkenyl and alkynyl is unsubstituted or substituted with 1 to 5 substituents independently selected from halo, nitro, cyano, oxo, C 6 -C 14 aryl, C 1 -Cgalkoxy, C 1 -C 8 alkoxycarbonyl, acyl, acyloxy, acylamino, amino, hydroxyl, carboxyl, carboxyl-C 1 -C 8 alkyl, thiol, thio-C 1 -C 8 alkyl, heterocyclyl with a 5- or 6-membered ring, and -OS 2 -C 1 -C 8 alkyl, and wherein each aryl, heteroaryl and heterocyclyl is unsubstituted or substituted with 1 to 5 substituents independently selected from halo, nitro, cyano, oxo, C 6 -C 14 aryl, C 1 -C 8 alkoxy, C 1 -C 8 alkyl, acyl, acylamino, amino, hydroxyl, carboxyl, carboxylC 1 -C 8 alkyl, thiol, thioC 1 -C 8 alkyl, heterocyclyl with a 5- or 6-membered ring, and -OS 2 -C 1 -C 8 alkyl; (ii) substituted C 1 -C 4 alkyl-C - where the substitution is one or more substituents selected from acyloxy, CH 3 OCH 2 CH 2 OCH 2 C O-, (acetyl-OCH 2) 2 CHN(acetyl)-, (acetylOCH 2) 2 CHN(Me)-, t -BuOC NH-, PhCH 2 OC NH- and C 1 -C 8 alkoxycarbonyl; and (iii) a moiety of the formula: wherein each R 11a, R 11b,R 12a, R 12b, R 13a, R 13b, R 14a and R 14b is H; and wherein D is selected from (i) the group consisting of C 1 -C 8 alkyl-C -, perhaloalkyl-C -, C 2 -C 10 alkenyl-C -, C 2 -C 10 alkynyl-C -, C 6 -C 14 aryl-C -, heteroaryl-C - with a 5- or 6-membered ring, heterocyclyl-C - with a 5- or 6-membered ring and -P (OC 1 -C 8 alkyl) 2, wherein each alkyl, alkenyl and alkynyl is unsubstituted or substituted with 1 to 5 substituents independently selected from halo, nitro, cyano, oxo, C 6 -C 14 aryl, C 1 -Cgalkoxy, C 1 -C 8 alkoxycarbonyl, acyl, acyloxy, acylamino, amino, hydroxyl, carboxyl, carboxyl-C 1 -C 8 alkyl, thiol, thio-C 1 -C 8 alkyl, heterocyclyl with a 5- or 6-membered ring, and -OS 2 -C 1 -C 8 alkyl, and wherein each aryl, heteroaryl and heterocyclyl is unsubstituted or substituted with 1 to 5 substituents independently selected from halo, nitro, cyano, oxo, C 6 -C 14 aryl, C 1 -C 8 alkoxy, C 1 -C 8 alkyl, acyl, acylamino, amino, hydroxyl, carboxyl, carboxylC 1 -C 8 alkyl, thiol, thioC 1 -C 8 alkyl, heterocyclyl with a 5- or 6-membered ring, and -OS 2 -C 1 -C 8 alkyl; (ii) substituted C 1 -C 4 alkyl-C - where the substitution is one or more substituents selected from acyloxy, CH 3 OCH 2 CH 2 OCH 2 C O-, (acetyl-OCH 2) 2 CHN(acetyl)-, (acetylOCH 2) 2 CHN(Me)-, t -BuOC NH-, PhCH 2 OC NH- and C 1 -C 8 alkoxycarbonyl; and (iii) a moiety of the formula: (i) the group consisting of C 1 -C 8 alkyl-C -, perhaloalkyl-C -, C 2 -C 10 alkenyl-C -, C 2 -C 10 alkynyl-C -, C 6 -C 14 aryl-C -, heteroaryl-C - with a 5- or 6-membered ring, heterocyclyl-C - with a 5- or 6-membered ring and -P (OC 1 -C 8 alkyl) 2, wherein each alkyl, alkenyl and alkynyl is unsubstituted or substituted with 1 to 5 substituents independently selected from halo, nitro, cyano, oxo, C 6 -C 14 aryl, C 1 -Cgalkoxy, C 1 -C 8 alkoxycarbonyl, acyl, acyloxy, acylamino, amino, hydroxyl, carboxyl, carboxyl-C 1 -C 8 alkyl, thiol, thio-C 1 -C 8 alkyl, heterocyclyl with a 5- or 6-membered ring, and -OS 2 -C 1 -C 8 alkyl, and wherein each aryl, heteroaryl and heterocyclyl is unsubstituted or substituted with 1 to 5 substituents independently selected from halo, nitro, cyano, oxo, C 6 -C 14 aryl, C 1 -C 8 alkoxy, C 1 -C 8 alkyl, acyl, acylamino, amino, hydroxyl, carboxyl, carboxylC 1 -C 8 alkyl, thiol, thioC 1 -C 8 alkyl, heterocyclyl with a 5- or 6-membered ring, and -OS 2 -C 1 -C 8 alkyl; (ii) substituted C 1 -C 4 alkyl-C - where the substitution is one or more substituents selected from acyloxy, CH 3 OCH 2 CH 2 OCH 2 C O-, (acetyl-OCH 2) 2 CHN(acetyl)-, (acetylOCH 2) 2 CHN(Me)-, t -BuOC NH-, PhCH 2 OC NH- and C 1 -C 8 alkoxycarbonyl; and (iii) a moiety of the formula: