New bronchodilators. 3. Imidazo[4,5-c][1,8]naphthyridin-4(5H)-ones

Area of Science:

• Medicinal Chemistry
• Pharmacology
• Respiratory Medicine

Background:

• Theophylline is a common bronchodilator but has a narrow therapeutic index.
• Development of novel oral bronchodilators with improved efficacy and safety profiles is needed.

Purpose of the Study:

• To design and synthesize novel imidazol[4,5-c][1,8]naphthyridin-4(5H)-ones as potential bronchodilators.
• To evaluate the in vitro and in vivo bronchodilator activities of these new compounds.
• To identify structure-activity relationships for optimal bronchodilator effects.

Main Methods:

• Synthesis of a series of novel imidazol[4,5-c][1,8]naphthyridin-4(5H)-ones.
• In vitro assays for bronchodilator activity, including inhibition of carbachol-, histamine-, and leukotriene D4-induced contractions.
• In vivo studies using an antigen inhalation-induced bronchospasm model in guinea pigs.
• Evaluation of effects on adenosine binding, phosphodiesterase (PDE) IV inhibition, and histamine release from mast cells.

Main Results:

• Several synthesized compounds showed potent bronchodilator activity, exceeding that of theophylline.
• Phenyl and n-butyl substitutions at the 5-position were crucial for activity.
• Compound 23 (5-phenyl-1H-imidazo[4,5-c][1,8]naphthyridin-4(5H)-one) exhibited significant in vivo efficacy (MED = 1 mg/kg) and in vitro potency (IC50 = 2.2 microM).
• Compound 23 relaxed airway smooth muscle and inhibited PDE IV.
• Compound 23 did not affect adenosine binding but inhibited histamine release from mast cells.

Conclusions:

• The novel series of tricyclic heterocycles, imidazol[4,5-c][1,8]naphthyridin-4(5H)-ones, represents a promising new class of bronchodilators.
• Compound 23 is a potent bronchodilator with potential for further therapeutic development.
• The compounds appear to act directly on airway smooth muscle and may have additional anti-inflammatory properties.