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| Other names | LY195115 | 
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| Formula | C14H15N3O2 | 
| Molar mass | 257.293 g·mol−1 | 
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Indolidan is a small-molecule cardiotonic agent originally developed by Eli Lilly & Co. for the treatment of heart failure. [1] [2] Structurally classified as a 2-indolinone derivative, it acts primarily as a selective inhibitor of phosphodiesterase 3 (PDE3), thereby enhancing cardiac contractility by increasing intracellular cyclic AMP (cAMP) levels in cardiac myocytes. [3] Indolidan has been investigated in clinical settings for its potential to improve cardiac output in patients with heart failure, but development has not advanced beyond early-phase clinical trials due to concerns about safety and overall efficacy. [4]
Indolidan belongs to a class or family of chemicals that contain a pyridazinone ring. [5] [6] For example, it is structurally related to Levosimendan, pimobendan, siguazodan, zardaverine.
 
 A Friedel–Crafts acylation of 3,3-dimethyloxindole [19155-24-9] (4) with succinic anhydride (5) afforded 5-(3,3-dimethyloxindole)-4-oxobutyric acid, PC13620376 (6). Treatment with hydrazine afforded the pyridazinone ring closure, thus completing the synthesis of indolidan (7) proper. [7] [1] [8] [9]
 
 An alternative way to create 3,3-dimethyloxindole (4) starting material is from N'-phenylisobutyrohydrazide [5461-50-7]. Intramolecular ring closure is made to occur upon heating in calcium hydride. [10]
A radiolabelled synthesis with carbon-14 and deuterium has also been described. [10]