iv catalylsed release reactions are being 1 s u2212 1 and 100 s 1 a means is thus available for releasing the dp iv inhibitors in a precisely temporally defined manner when the enzymes are to have an immediate onset of action for example upon ingestion of glucose rich nutrient a compound a u2014 b u2014 c will be selected that has for example the amino acid gly as group a when the onset of action of the inhibitor is to be delayed the amino acid ile for example can be selected as group a by means of the prodrug compounds according to the invention therefore it is possible for dp iv inhibitors to be transported through the mucosa of the small intestine especially almost without a delay for example almost simultaneously with ingested nutrients when b represents a bond it is especially a peptide bond when b represents an amino acid it is linked to a and c preferably via peptide bonds on analysis of the dose effect relationships of the dp iv inhibitor isoleucyl thiazolidide as a modulator of the blood glucose concentration in the mammalian organism a difference can be found between oral and parenteral administration of the active substance to wistar rats on oral administration saturation was observed in the uptake of the active substance measured on the basis of inhibition of the serum enzyme whereas on parenteral administration of the inhibitor complete inhibition of the enzyme was observed that is demonstrated by way of example in table 1 in view of the fact that in the intestine there are also present enzymes especially high concentrations of dp iv that are capable of cleaving the cleavable.