INTERACTION OF N-BENZOYL-D-PHENYLALANINE AND RELATED-COMPOUNDS WITH THE SULFONYLUREA RECEPTOR OF BETA-CELLS

1 The structure activity relationships for the insulin secretagogues N -benzoyl-D-phenylalanine (NBDP) and related compounds were examined at the sulphonylurea receptor level by use of cultured HIT-TIS and mouse pancreatic beta-cells. The affinities of these compounds for the sulp honylurea receptor were compared with their potencies for K-ATP-channe l inhibition. In addition, the effects of cytosolic nucleotides on K-A TP-channel inhibition by NBDP were investigated.2 NBDP displayed a dis sociation constant for binding to the sulphonylurea receptor (K-D valu e) of 11 mu M and half-maximally effective concentrations of K-ATP-cha nnel inhibition (EC50 values) between 2 and 4 mu M (in the absence of cytosolic nucleotides or presence of 0.1 mM GDP or 1 mM ADP). 3 In the absence of cytosolic nucleotides or presence of GDP (0.1 mM) maximall y effective concentrations of NBDP (0.1-1 mM) reduced K-ATP-channel ac tivity to 47% and 44% of control, respectively. In the presence of ADP (1 mM), K-ATP-channel activity was completely suppressed by 0.1 mM NB DP. 4 The L-isomer of N-benzoyl-phenylalanine displayed a 20 fold lowe r affinity and an 80 fold lower potency than the D-isomer. 5 Introduct ion of a p-nitro substituent in the D-phenylalanine moiety of NBDP did not decrease lipophilicity but lowered affinity and potency by more t han 30 fold. 6 Introduction of a p-amino substituent in the D-phenylal anine moiety of NBDP (N-benzoyl-p-amino-D-phenylalanine, NBADP) reduce d lipophilicity and lowered affinity and potency by about 10 fold. Thi s loss of affinity and potency was compensated for by formation of the phenylpropionic acid derivative of NBADP. A similar difference in aff inity was observed for the sulphonylurea carbutamide and its phenylpro pionic acid derivative. 7 Replacing the benzene ring in the D-phenylal anine moiety of NBDP by a cyclohexyl ring increased lipophilicity, and the K-D and EC50 values were slightly lower than for NBDP. Exchange o f both benzene rings in NBDP by cyclohexyl rings further increased lip ophilicity without altering affinity and potency. 8 This study shows t hat N-acylphenylalanines interact with the sulphonyrurea receptor of p ancreatic beta-cells in a stereospecific manner. Their potency depends on lipophilic but not aromatic properties of their benzene rings. As observed for sulphonylureas, interaction of N-acylphenylalanines with the sulphonylurea receptor does not induce complete inhibition of K-AT P-channel activity in the absence of inhibitory cytosolic nucleotides.