Essential structure of orexin 1 receptor antagonist YNT-707, Part II: Drastic effect of the 14-hydroxy group on the orexin 1 receptor antagonistic activity

Abstract The 14-dehydration- and 14-H derivatives of the orexin 1 receptor (OX 1 R) antagonist YNT-707 ( 2 ) were synthesized. The obtained derivatives showed higher affinities for OX 1 R than the corresponding 14-hydroxy derivatives. The conformational analysis suggested that the 17-sulfonamide groups in the derivatives without the 14-hydroxy group have a greater tendency to be oriented toward the upper side of the D-ring compared with the 14-hydroxy derivatives. Additionally, the 14-dehydration-derivative with 6α-amide side chain showed significantly higher affinity than the 14-hydroxy derivative, while the corresponding 14-H derivative showed only slightly higher affinity. Thus, the 14-hydroxy group strongly affects the affinity of the antagonist for the OX 1 R.