Adrenergic agonists structures

Brimonidine and the less lipid-soluble and less receptor-selective apraclonidine are 2-adrenergic agonists structurally similar to cloni-dine. Apraclonidine is indicated and brimonidine is effective for prevention or control of postoperative or postlaser treatment increases in lOP and both are indicated in the treatment of open-angle glaucoma. Brimonidine is considered a first-line or adjunctive agent in the therapy of POAG, and apraclonidine is seen as a second-line or adjunctive therapy. 

The imidazoline receptor is a hypothetical receptor for a subgroup of a2 adrenergic agonists, which are characterized by their imidazoline structure (e.g. moxoni-dine). So far, there is no proof of the existence of imidazoline receptors. 

Figure 3 Structures of phenethanolamine /3-adrenergic agonists of potential human food safety concern. Multi-residue methods have been developed with the goal of broad cross-reactivity so that simultaneous screening may occur efforts have not been particularly successful...

In contrast to this, there are no such structural constraints on a-adrenergic agonists or antagonists. Some of the most active a-sympathomimetic agents in fact contain an imidazoline moiety as part of the pharmacophore. The appropriate ring system can be... 

The direct-acting adrenomimetics described next are a-adrenergic agonists that are structurally very different from the drugs described above. 

Clonidine is a selective o -adrenergic agonist. Clonidine has expressed hypotensive action, which is associated with a reduction of general peripheral vascular resistance, reduced frequency of cardiac beats, and a reduction of cardiac output. The mechanism of action of clonidine is caused by stimulation of o -adrenoreceptors of the inhibitory structures of the brain as well as a reduction of sympathetic impulses to the blood vessels and brain. 

Tolazoline Tolazoline, 2-benzyl-2-imidazoline (12.2.7), is synthesized by the heterocy-clation of the ethyl ester of iminophenzylacetic acid with ethylendiamine (12.2.6), which forms the desired product (12.2.7) [32-35]. The structure of tolazoline is strikingly similar to a-adrenergic agonists, which are antiedema sympathomimetics. 

A structurally very simple carboxylic acid, modafinil (62-4), increases alertness and inhibits narcolepsy as a result of its activity as a cerebral ai-adrenergic agonist. The short synthesis begins with the reaction of benzhydrol proper (62-1) with chloroacetic... 

Fig. 8.2 Chemical structures of commonly used -adrenergic agonists.

Figure 1.7. Structures of the natural adrenergic agonists, norepinephrine and epinephrine, and the synthetic p-selective agonist isoproterenol.

Phenylephrine is a selective ai adrenergic agonist, with a pharmacological structure similar to norepinephrine (noradrenaline), which causes peripheral vasoconstriction. Stimulation of adrenoceptors in the myocardium has an inotropic effect. However, phenylephrine produced no increase in cardiac output, increased systemic vascular resistance and mean arterial pressure and reduced muscle blood flow in anaesthetized horses (Lee et al 1998). Phenylephrine should be reserved for critical conditions where the perfusion of essential organs is compromised and inotropes are not effectively maintaining organ function. The recommended infusion rates are shown in Table 12.3. 

Synonyms Salbutamol Ventolin Proventil Apo-Salvent Novo-Salmol Albuterol sulfate Volmax Chemical/Pharmaceutical/Other Class Selective jSi-adrenergic agonist Chemical Formula C13H21O3 Chemical Structure ... 

When an SPE sorbent shows good performance with an analyte its fitness for other analytes, however close in structure, should be experimentally confirmed. A case in point is the forensic analysis of the adrenergic agonists Clenbuterol (70) and Compound A (71), both forbidden for use as animal feed additives. Four types of sorbents were tested—cyanopropyl resin, sulfonic acid SCX, mixed SCX + Qg and nonendcapped ( is only the latter type was found to quantitatively extract 71 although the performance of all four was satisfactory for 70. End analysis was by GC-MS-MS127. 

The structures of the phenylethylamine adrenergic agonists were summarized in Table 1.2. Agents of this type have been extensively... 

Tolazoline and the structurally related imidazoline tetrahydrozoline may be H2 receptor agonists since tolazoline-induced acid stimulation in the dog can be blocked by burimamide, metiamide and cimetidine and both imidazolines induce characteristic -agonist effects on isolated guinea pig atria preparations which can be blocked by metiamideJ Clonidine, like the imidazolines, has a-adrenergic agonist activity... 

Fluorine-Substituted Retinal and Rhodopsin. Liu and coworkers (31) have found that fluorine substitution on carbon-10 of retinal alters the photochemical and spectral properties of the derived rhodopsin. They proposed that a glutamate residue (Glu122) on the visual protein, situated near C-13 of opsin-bound retinal, interacts with the electron-rich C-F bond. As noted above, rhodopsin and p-adrenergic receptors have structural homology. A relationship between the effects of fluorine substitution on the biochemestry of adrenergic agonists and of retinal at this time can be only a matter of speculation. 

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