A compound of general formula: wherein 1 ------ 2, 2 ------ 3, 3 ------ 4 are each independently a single or double bond; R a is selected from a straight or branched C 1 -C 5 alkyl, straight or branched C 2 -C 5 alkenyl, straight or branched C 2 -C 5 alkynyl and -C(=O)R d, each optionally substituted by at least one group selected from -OH, -COOH, -NH 2, C 1 -C 5 amine, halogen, phenyl, heteroaryl; wherein R d is selected from the group consisting of -H, -OH, straight or branched C 1 -C 5 alkyl, straight or branched C 2 -C 5 alkenyl, straight or branched C 2 -C 5 alkynyl, straight or branched C 1 -C 5 alkoxy, -NR e R f; R e and R f are each independently selected from H and straight or branched C 1 -C 5 alkyl; and R b and R c are each independently selected from -H, -OH, =O, =CR g R h, =NR i, =S, and a group of formula (II'): wherein R j, R k and R mm are each independently selected from H, and -OR n, wherein R n is selected form H, -COOR t, a straight or branched C 1 -C 5 alkyl optionally substituted by at least one group selected from -COOH, -NH 2, provided that at least one of R j and R k is different than H; R m is selected from an optionally substituted straight or branched C 3 -C 12 alkyl, an optionally substituted straight or branched C 5 -C 9 alkoxy, an optionally substituted straight or branched C 1 -C 7 ether; and R t is selected from H, and C 1 -C 5 alkyl; and wherein Rg, R h, and R i are each independently selected from H, straight or branched C 1 -C 5 alkyl, straight or branched C 1 -C 5 alkoxy and -NH 2; and wherein at least one of R b and R c is a group of formula (II'). 1 ------ 2, 2 ------ 3, 3 ------ 4 are each independently a single or double bond; R a is selected from a straight or branched C 1 -C 5 alkyl, straight or branched C 2 -C 5 alkenyl, straight or branched C 2 -C 5 alkynyl and -C(=O)R d, each optionally substituted by at least one group selected from -OH, -COOH, -NH 2, C 1 -C 5 amine, halogen, phenyl, heteroaryl; wherein R d is selected from the group consisting of -H, -OH, straight or branched C 1 -C 5 alkyl, straight or branched C 2 -C 5 alkenyl, straight or branched C 2 -C 5 alkynyl, straight or branched C 1 -C 5 alkoxy, -NR e R f; R e and R f are each independently selected from H and straight or branched C 1 -C 5 alkyl; and R d is selected from the group consisting of -H, -OH, straight or branched C 1 -C 5 alkyl, straight or branched C 2 -C 5 alkenyl, straight or branched C 2 -C 5 alkynyl, straight or branched C 1 -C 5 alkoxy, -NR e R f; R e and R f are each independently selected from H and straight or branched C 1 -C 5 alkyl; and R b and R c are each independently selected from -H, -OH, =O, =CR g R h, =NR i, =S, and a group of formula (II'): wherein R j, R k and R mm are each independently selected from H, and -OR n, wherein R n is selected form H, -COOR t, a straight or branched C 1 -C 5 alkyl optionally substituted by at least one group selected from -COOH, -NH 2, provided that at least one of R j and R k is different than H; R m is selected from an optionally substituted straight or branched C 3 -C 12 alkyl, an optionally substituted straight or branched C 5 -C 9 alkoxy, an optionally substituted straight or branched C 1 -C 7 ether; and R t is selected from H, and C 1 -C 5 alkyl; and wherein Rg, R h, and R i are each independently selected from H, straight or branched C 1 -C 5 alkyl, straight or branched C 1 -C 5 alkoxy and -NH 2; and wherein at least one of R b and R c is a group of formula (II').