Compounds attachable to skin

A topical composition comprising a compound of formula (I),

• or a tautomer and/or a pharmaceutically acceptable salt thereof,
• wherein A1, A2 and A3 independently from each other represent,
• a) a color-imparting moiety,
• b) a UVA and/or UVB absorbing moiety, or
• c) a C1-C30 moiety, H, hydroxyl, amino, or a halogen;
• wherein R1 represents hydrogen or a protective group hydrolysable under physiological conditions after application of the topical composition onto skin,
• wherein L1, L2 and L3 independently from each other represent a linker group or are absent, and
• wherein L1-A1 and L2-A2 do not represent a moiety comprising an unsaturated C—C or C—N bond in alpha-position to the carbon atom marked “a” and “b”, respectively;
• and an excipient suitable for topical administration.

A compound of formula (IV):

• or a pharmaceutically acceptable salt thereof, wherein:
• R1 is selected from H and a carboxylic acid-protecting group;
• R2 is selected from H or a protective group hydrolysable under physiological conditions after application in a topical composition onto skin;
• and
• R3 is selected from C1-6 alkyl, C2-6 alkenylene, C2-6 alkynylene, C(O)Rb1, C(O)NRc1Rd1, C(O)ORa2 and oxo, wherein each of said C1-6 alkyl, C2-6 alkenylene, and C2-6 alkynylene is optionally substituted with 1 or 2 substituents independently selected from ORa1, NRc1Rd1, C(O)Rb1, C(O)NRc1Rd1, and C(O)ORa2;
• or wherein R3 and OR2, together with the carbon atoms to which they are attached form a tetrahydrofuran ring, which is optionally substituted with ORa1 or oxo;
• each Ra1 is independently selected from H, C1-6 alkyl, C1-4 haloalkyl, C2-6 alkenyl, C2-6 alkynyl, and a hydroxyl-protecting group;
• each Ra2 is independently selected from H, C1-6 alkyl, C1-4 haloalkyl, C2-6 alkenyl, C2-6 alkynyl, and a carboxyl-protecting group;
• each Rc1 and Rd1 is independently selected from H, C1-6 alkyl, C1-4 haloalkyl, C2-6 alkenyl, C2-6 alkynyl, and an amino-protecting group;
• and
• each Rb1 is independently selected from H, C1-6 alkyl, C1-4 haloalkyl, C2-6 alkenyl, and C2-6 alkynyl.