The present invention relates to the C-13 molecule (methyl 2-{5-[(3-benzyl-4-oxo-2-thioxo-1,3-thiazolidin-5-ylidene)methyl]-2-furyl}-benzoate) and to organic molecules functionally equivalent to the C-13 molecule, capable of inhibiting the binding of an antibody or antibody fragment with the human Syk protein tyrosine kinase, to the use of these molecules for the production of medicaments for the prevention or treatment of diseases dependent on metabolic pathways involving Syk, and also to a method for identifying such molecules.