wherein:

n is an integer of 0, 1, or 2

X represents —S(O)_m—, —(C═O)— or a single bond, wherein m is an integer of 0, 1, or 2, with the proviso that when X represents —(C═O)—, then n is 0,

R represents hydrogen or is a residue R^a, which residue R^a is selected from the group consisting of:

C_1-6 alkyl;

C_2-6 alkenyl;

C_3-8 cycloalkyl;

C_3-8 cycloalkyl, wherein one CH₂ group is replaced by O, S, NH or NCH₃;

C_4-8 cycloalkenyl;

C_4-8 cycloalkenyl, wherein one CH₂ group is replaced by O, S, N or NCH₃;

phenyl;

pyridyl;

thiophenyl;

nitrosyl;

S-cysteinyl;

S-glutathionyl; and

wherein R* is selected from the group consisting of hydrogen, C_1-6 alkyl, C_2-6 alkenyl, C_3-8 cycloalkyl; C_4-8 cycloalkenyl, acetyloxy, hydroxyl, ONO₂ and halogen,

wherein R^a optionally is substituted by one to three groups independently selected from C_1-6 alkyl, C_2-6 alkenyl, C_3-8 cycloalkyl, C_4-8 cycloalkenyl, acetyloxy, hydroxyl, ONO₂ and halogen,

provided that when RXS(O)_n— and —ONO₂ are trans to each other with respect to the ring plane as depicted in formulae (Ia) and (Ib):

then RXS(O)_n— does not represent

wherein Z is an C₁-C₄ alkyl group, aryl group, or an aralkyl group.