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Cyclic analogues of N-[3,5-bis(trifluoromethyl)benzyl]-7,8-dihydro-N, 7-dimethyl-5-(4-methylphenyl)-8-oxo-1,7-naphthyridine-6-carboxamide (1) having a 6-9-membered ring (6-9) were synthesized and evaluated for NK(1) antagonistic activities. The 8-membered ring compound with a beta-methyl group at the C((9))-position, (aR,9R)-7-[3, 5-bis(trifluoromethyl)benzyl]-8,9,10, 11-tetrahydro-9-methyl-5-(4-methylphenyl)-7H-[1,4]diazocino[2,1-g] [1, 7]naphthyridine-6,13-dione [(aR,9R)-8b], was atropodiastereoselectively synthesized by cyclization of a chiral intermediate, 10g. On the other hand, the 7-membered ring compound with a beta-methyl group at the C((9))-position [(9S)-7b] was obtained as an equilibrium mixture of atropisomers with a ratio of ca. 3:2 in solution at room temperature (measured by NMR in CDCl(3)). Compounds (9S)-7b and (aR,9R)-8b exhibited excellent antagonistic activities both in vitro [IC(50) (inhibition of [(125)I]BH-SP binding in human IM-9 cells) = 0.28 and 0.45 nM, respectively] and in vivo (iv and po). Significantly, the in vitro activity of (aR, 9R)-8b was ca. 750-fold higher than that of its enantiomer (aS, 9S)-8b, ca. 40-fold higher than its atropisomer (aS,9R)-8b, and ca. 20-fold higher than its diastereomer (aR,9S)-8b. The structure-activity relationships in this series, along with the X-ray analysis of (aR,9R)-8b, indicated that the stereochemistry around the -C((6))(=O)-N((7))-CH(2)Ar moiety is important for NK(1) receptor recognition. The NK(1) antagonists showed effects on bladder functions in guinea pigs upon intravenous injection: i.e., the antagonists increased the shutdown time of distension-induced rhythmic bladder contractions and the bladder volume threshold, and the effects on the shutdown time were found to correlate well with the NK(1) antagonistic activities. Compound (aR,9R)-8b has been identified as a potential clinical candidate for the treatment of bladder function disorders.

A series of 4-phenylisoquinolone derivatives were synthesized and evaluated for NK1 (substance P) antagonist activity. Highly potent antagonists, 4-phenyl-3-isoquinolone-N-benzylcarboxamides (11), were discovered from the structure-activity relationship studies on the isoquinolone-urea lead 1a. Optimization of the activity in this series resulted in the development of 5-phenyl-6-pyrido[3,4-b]pyridine-N-benzylcarboxamides (30) which are highly potent orally active NK1 antagonists. Among the compounds synthesized, N-[3,5-bis(trifluoromethyl)benzyl]-7,8-dihydro-N,7-dimethyl-8-oxo-5- (substituted phenyl)-6-pyrido[3,4-b]pyridinecarboxamides (30a,f,g) showed excellent antagonist activities with IC50 values (in vitro inhibition of [125I]-BH-SP binding in human IM-9 cells) of 0.21-0.34 nM and ED50 values (in vivo inhibition of capsaicin-induced plasma extravasation in guinea-pig trachea, iv) of 0.017-0.030 mg/kg. These compounds exhibited significantly potent activity upon oral administration with ED50 values of 0.068-0.17 mg/kg. Conformational studies on 30g indicated that the two stable conformers of 30g are quite similar to those of CP-99,994.

A potent and orally active NK1 antagonist, trans-N-[3, 5-bis(trifluoromethyl)benzyl]-7,8-dihydro-N, 7-dimethyl-5-(4-methylphenyl)-8-oxo-1,7-naphthyridine-6-carboxamide (1t), was shown to exist as a mixture of separable and stable (R)- and (S)-atropisomers (1t-A and 1t-B) originating from the restricted rotation around the -C(6)-C(=O)- bond; the antagonistic activities of 1t-A were ca. 6-13-fold higher than those of 1t-B. Analogues of 1t (3), which have (S)- and (R)-methyl groups at the benzylic methylene portion of 1t, were prepared and separated into the diastereomeric atropisomers, 3a-A, 3a-B and 3b-A, 3b-B, in enantiomerically pure forms. Among the four isomers of 3, the (aR, S)-enantiomer (3a-A) exhibited the most potent antagonistic activities with an IC50 value of 0.80 nM (in vitro inhibition of [125I]BH-SP binding in human IM-9 cells) and ED50 values of 9.3 micrograms/kg (iv) and 67.7 micrograms/kg (po) (in vivo inhibition of capsaicin-induced plasma extravasation in guinea pig trachea), while the activity of the (aS,R)-enantiomer (3b-B) was the weakest with an IC50 value of 620 nM. The structure-activity relationships in this series of antagonists indicate that the (R)-configuration at the axial bond and the stacking (or stacking-like) conformation between the two phenyl rings as shown in 1t-A and 3a-A are essential for high-affinity binding and suggest that the amide moiety functions as a hydrogen bond acceptor in the interaction with the receptor.

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