A novel series of 8-(2-substituted morpholino)-9,1-[(N-methylimino)methano]-7-fluoro-5-oxo-5H-thiazolo[3,2-a]quinoline-4-carboxylic acids, designated 8a-j, with a unique tetracyclic structure were synthesized, and the in vitro and in vivo antibacterial activities against Gram-positive strains, including methicillin-resistant Staphylococcus aureus isolates (MRSA), and Gram-negative strains were evaluated. These morpholino derivatives, 8a-j, showed excellent in vitro antibacterial activities against Gram-positive bacteria. The substitutions at the C-2 position of the 8-morpholino moiety of compound 8 play an important role in the enhancement of in vivo antibacterial activity. The unsubstituted morpholino derivative 8a, the 2,6-dimethyl derivative 8c, and the 2-ethylmorpholino derivative 8d showed poor in vivo antibacterial activity, while 8b, 8f-h, and 8j exhibited good activities. The 2-(methoxymethyl)morpholino derivative, 8h, showed the most potent activity in vivo. The therapeutic effects of 8h on systemic infection against S. aureus IID 803 were over 10-fold more potent than that of ofloxacin. Compound 8h, which showed superior oral bioavailability, has a chiral center. The enantiomers of 8h were synthesized, and the in vitro and in vivo antibacterial activities were evaluated. Both enantiomers, (S)-8h and (R)-8h, and the racemic compound 8 exhibited similar activities in vitro and in vivo. Compounds 8b and 8f-h also showed good levels of antibacterial activity against MRSA strains. The morpholino derivatives with unique tetracyclic structures are characterized by strong antibacterial activities against MRSA strains.
All Science Journal Classification (ASJC) codes
- Molecular Medicine
- Drug Discovery