Optically active compounds

An optically active butane-1,2,3,4-tetraol derivative of formula I:

• in which
• A1, A2, A3, A4 each independently represents hydrogen;
• or an optionally-substituted methyl group;
• or an optionally-substituted aliphatic group with 2 to 80 C-atoms, in which one or more C-atoms may be replaced by a heteroatom or a group —SO—, —SO2—, —SOO—, —OSO— or —SOS—;
• or an optionally-substituted aromatic or non-aromatic carbocyclic or heterocyclic ring system, with 2 to 80 C-atoms;
• and
• A5, A6, A7, A8 each independently represents an optionally-substituted aliphatic group with 3 to 80 C-atoms, in which a C-atom, or two or more non-adjacent C-atoms, may be replaced by a heteroatom or a group —SO—, —SO2—, —SOO—, —OSO— or —SOS—;
• or an optionally-substituted aromatic or non-aromatic carbocyclic or heterocyclic ring system, with 2 to 80 C-atoms;
• or
• one, two or three of A5, A6, A7 and A8 independently represents hydrogen;
• or an optionally-substituted methyl group;
• or an optionally-substituted aliphatic group with 2 C-atoms, in which a C-atom may be replaced by a heteroatom or a group —SO—, —SO2—, —SOO—, —OSO— or —SOS—;
• and the remainder of A5, A6, A7, A8 independently represent an optionally-substituted aliphatic group with 3 to 80 C-atoms, in which a C-atom, or two or more non-adjacent C-atoms, may be replaced by a heteroatom or a group —SO—, —SO2—, —SOO—, —OSO— or —SOS—;
• or an optionally-substituted aromatic or non-aromatic carbocyclic or heterocyclic ring system, with 2 to 80 C-atoms;
• with the provisos that:
• when one, two or three of A5, A6, A7 and A8 represents hydrogen, then A5, A6, A7 and A8 may not represent COOH;
• and
• when A5, A6, A7 and A8 are all phenyl, then at least one of A1, A2, A3, A4 does not represent hydrogen.