Temocapril is an ACE inhibitor. It was not approved for use in the US. It is administered as inactive prodrug, then converted to its active metabolite, temocaprilat. It was patented in 1984 and approved for medical use in 1994. Chemically the API is supplied most commonly as the hydrochloride salt and appears as a white to off white crystalline powder with molecular properties that enable oral formulation development. Temocapril is hydrolyzed in vivo by esterases to the carboxylate temocaprilat which binds the zinc-containing active site of angiotensin converting enzyme leading to inhibition of angiotensin II formation. Key technical attributes relevant to development and quality control include low aqueous solubility of the free base versus improved solubility of the hydrochloride salt, stereochemical purity requirements, stability profile under forced degradation conditions, and characteristic chromatographic and spectroscopic fingerprints used for identity and assay including reversed phase HPLC, LC-MS and NMR.
Process related impurities and degradation products observed during synthesis and storage are typically small molecule related compounds such as de-esterified temocaprilat, ring-opened or oxidized analogues, stereoisomeric impurities and low level residual solvents. Typical quality specifications for an API batch release set limits by impurity class, for example individual known related compounds are often controlled to not greater than 0.1 to 0.3 percent by area or mass, unspecified impurities are commonly limited to 0.05 to 0.10 percent, and total impurities or total related compounds are typically limited to about 1.0 percent, with exact limits defined by the product specific specification and regulatory guidance. Additional controls include residual solvents per ICH Q3C, elemental impurities monitored per ICH Q3D and water content by Karl Fischer. Identification and quantitation of impurities are performed by validated chromatographic methods with orthogonal confirmation by LC-MS and NMR when required.
Temocapril hydrochloride is the hydrochloride salt form of temocapril used to improve handling and aqueous solubility for formulation; it retains the prodrug motif and is converted in vivo to the active carboxylate temocaprilat. The hydrochloride salt is characterized by its crystalline form, melting point range, and specific analytical signature by HPLC, IR and NMR for identity and purity testing.
Temocapril is designed as an ester prodrug that is hydrolyzed by plasma and hepatic esterases to yield the active diacid temocaprilat; this metabolic conversion increases the concentration of the potent ACE inhibitor at systemic circulation and determines onset and duration of pharmacodynamic effect.
Common impurities include de-esterified temocaprilat, oxidative and hydrolytic degradation products, stereoisomeric impurities and trace residual solvents or elemental impurities; control is achieved by defined process controls, in-process testing and a final specification that typically limits individual known impurities to about 0.1 to 0.3 percent and total impurities to about 1.0 percent, with limits for residual solvents and elemental impurities set by ICH guidelines.
Primary methods include validated reversed phase HPLC with UV detection for assay and impurity profiling, LC-MS for impurity identification and mass confirmation, NMR for structural confirmation and stereochemical assessment, Karl Fischer titration for water content, and ICP or ICP-MS for elemental impurity determination.
