Patent Update: Angiotensin-II Antagonists: Patent Activity since the Discovery of DuP-753

An efficient synthesis of a rationally designed 1,5 disubstituted imidazole AT(1) angiotensin II receptor antagonist: reorientation of imidazole pharmacophore groups in losartan reserves high receptor affinity and confirms docking studies

A new 1,5 disubstituted imidazole AT(1) Angiotensin II (AII) receptor antagonist related to losartan with reversion of butyl and hydroxymethyl groups at the 2-, 5-positions of the imidazole ring was synthesized and evaluated for its antagonist activity (V8). In vitro results indicated that the reorientation of butyl and hydroxymethyl groups on the imidazole template of losartan retained high binding affinity to the AT(1) receptor concluding that the spacing of the substituents at the 2,5- positions is of primary importance. The docking studies are confirmed by binding assay results which clearly show a comparable binding score of the designed compound V8 with that of the prototype losartan. An efficient, regioselective and cost effective synthesis renders the new compound as an attractive candidate for advanced toxicological evaluation and a drug against hypertension.

Synthesis, binding studies and in vivo biological evaluation of novel non-peptide antihypertensive analogues

AT(1) antagonists (SARTANs) constitute the last generation of drugs for the treatment of hypertension, designed and synthesized to mimic the C-terminal segment of the vasoconstrictive hormone angiotensin II (AngII). They exert their action by blocking the binding of AngII on the AT(1) receptor. Up to date eight AT(1) antagonists have been approved for the regulation of high blood pressure. Although these molecules share common structural features and are designed to act under the same mechanism, they have differences in their pharmacological profiles and antihypertensive efficacy. Thus, there is still a need for novel analogues with better pharmacological and financial profiles. An example of a novel synthetic non peptide AT(1) antagonist which devoids the classical template of SARTANs is MM1. In vivo studies showed that MMK molecules, which fall in the same class of MM1, had a significant antihypertensive (40-80% compared to the drug losartan) activity. However, in vitro affinity studies showed that losartan has considerably higher affinity. The theoretical docking studies showed that MM1 acts on the same site of the receptor as losartan. They exert hydrophobic interactions with amino acid Val108 of the third helix of the AT(1) receptor and other hydrophobic amino acids in spatial vicinity. In addition, losartan favours multiple hydrogen bondings between its tetrazole group with Lys199. These additional interactions may in part explain its higher in vitro binding affinity.

Losartan: a selective angiotensin II type 1 (AT1) receptor antagonist for the treatment of heart failure

Losartan (COZAAR) is the prototype of a new class of potent and selective angiotensin II (AII) type 1 (AT(1)) receptor antagonists with the largest published preclinical and clinical data base. Since all of the AII antagonists are selective for the AT(1) receptor, these drugs should exhibit similar cardiovascular effects. However, since the pharmacokinetic/pharmacodynamic profiles of these agents and their degree of affinity for the AT(1) receptor differ, it is likely that differences in clinical profiles between these drugs exist and will require investigation. Losartan (parent compound), has moderate affinity for the AT(1) receptor (competitive inhibition). Losartan is well-absorbed orally as an active drug and is rapidly converted via oxidation in the human liver to a more potent metabolite (designated E3174) with an affinity 20- to 30-times greater for the AT(1) receptor (non-competitive inhibition). E3174 has a half-life of 6 - 9 h; elimination is via renal and hepatic routes. Antihypertensive and, in heart failure patients, haemodynamic activity is observed over a 24 h period with once daily dosing. Over 6 million patients have been treated for hypertension with continued excellent tolerability. Clinical experience in heart failure is growing, and recent data suggest an improved survival with losartan versus captopril, a drug from the angiotensin-converting-enzyme inhibitor class with proven benefit in this population. The current comprehensive losartan clinical end-point programme (4 large scale morbidity/mortality trials) should provide evidence regarding the efficacy of direct blockade of the AT(1) receptor with losartan compared to standard therapy: 1) The Losartan Heart Failure Survival Study - ELITE II, 2) The Losartan Post-Myocardial Infarction Survival Study - OPTIMAAL, 3) The Losartan Hypertension Survival Study - LIFE and 4) The Losartan Renal Protection Study - RENAAL.

5-Substituted-1H-tetrazoles as carboxylic acid isosteres: medicinal chemistry and synthetic methods

5-Substituted-1H-tetrazoles (RCN4H) are often used as metabolism-resistant isosteric replacements for carboxylic acids (RCO2H) in SAR-driven medicinal chemistry analogue syntheses. This review provides a brief summary of the medicinal chemistry of tetrazolic acids and highlights some examples of tetrazole-containing drug substances in the current literature. A survey of representative literature procedures for the preparation of 5-substituted-1H-tetrazoles, focusing on preparations from aryl and alkyl nitriles, is presented in sections by generalized synthetic methods.

Does blockade of angiotensin II receptors offer clinical benefits over inhibition of angiotensin-converting enzyme?

Angiotensin AT1 receptor antagonists represent a new class of drugs for the treatment of hypertension. They are specific for the renin-angiotensin system, selective for the angiotensin AT1 receptor, and act independently of the angiotensin II synthetic pathway. Blockade of the renin-angiotensin system at the receptor level should therefore be more complete. The high circulating levels of angiotensin II following angiotensin AT1 receptor blockade could be beneficial in stimulating other unblocked angiotensin receptors, especially the AT2 receptor. It has been proposed that the angiotensin AT2 receptor, which is re-expressed or up-regulated during pathological circumstances, counterbalances the effect of the stimulation of the angiotensin AT1 receptor. Through this mechanism, angiotensin AT1 antagonists may be superior to ACE inhibitors in cardiac and vascular remodelling as well as in kidney insufficiency. Long-term trials are required to demonstrate the possible clinical superiority of this new class of antihypertensive agents.