1,3-Dipropyl-8-phenylxanthine

[3H]xanthine amine congener of 1,3-dipropyl-8-phenylxanthine: an antagonist radioligand for adenosine receptors.[Pubmed:3012550]

Proc Natl Acad Sci U S A. 1986 Jun;83(11):4089-93.

An amine-functionalized derivative of 1,3-Dipropyl-8-phenylxanthine has been prepared in tritiated form as a xanthine amine congener ([3H]XAC) for use as an antagonist radioligand for adenosine receptors. [3H]XAC has higher receptor affinity, higher specific activity, lower nonspecific membrane binding, and more favorable hydrophilicity than 1,3-diethyl-8-[3H]phenylxanthine, the xanthine commonly used for adenosine receptor binding. In rat cerebral cortical membranes, [3H]XAC exhibits saturable, specific binding with a Kd of 1.23 nM and a Bmax of 580 fmol/mg of protein at 37 degrees C. N6-(R-Phenylisopropyl)adenosine is a more potent inhibitor of [3H]XAC binding than is 5'-N-ethylcarboxamidoadenosine, indicating that binding is to an A1-adenosine receptor. In the absence of GTP, the inhibition curves for adenosine agonists versus [3H]XAC binding are biphasic, indicating that [3H]XAC is binding to low- and high-affinity agonist states of the A1 receptor. In the presence of GTP, adenosine analogs exhibit monophasic, low-affinity inhibition of binding of [3H]XAC. Inhibition of [3H]XAC binding by theophylline or by various 8-phenylxanthines is monophasic, and the potencies are commensurate with the potencies of these xanthines as adenosine receptor antagonists. The receptor sites in calf brain membranes exhibit a higher affinity (Kd = 0.17 nM) for [3H]XAC, whereas sites in guinea pig exhibit a slightly lower affinity (Kd = 3.0 nM). Densities of [3H]XAC binding sites are similar in brain membranes from all species.

[Selectivity of the action of 1,3-dipropyl-8-phenylxanthine on the purine receptors of the intestines].[Pubmed:3191974]

Farmakol Toksikol. 1988 Jul-Aug;51(4):60-2.

In experiments on the isolated ileum of guinea pigs and rats it was shown that 1,3-Dipropyl-8-phenylxanthine (DPPX) is a highly potent adenosine antagonist blocking A1-adenosine receptors of the myenteric plexus (pA2 = 7.29 +/- 0.06) and allosterically modulating affinity of A2-receptors of the intestinal smooth muscles to adenosine (pA2 = 6.64 +/- 0.05). DPPX exerted no influence on purinergic (PR2), adrenergic and opiate receptors of the nervous and muscular cells of the intestine. Exceeding the activity of theophylline by 339-87 times, DPPX failed to exert the selective effect on A1- and A2-subtypes of adenosine receptors.

Analogues of 1,3-dipropyl-8-phenylxanthine: enhancement of selectivity at A1-adenosine receptors by aryl substituents.[Pubmed:3016270]

J Med Chem. 1986 Aug;29(8):1520-4.

The effect of a variety of aryl substituents on the potency and selectivity of 19 analogues of 1,3-Dipropyl-8-phenylxanthine as antagonists at A1- and A2-adenosine receptors in brain tissue was determined. The 4-sulfamoylphenyl and 4-carbamoylphenyl analogues are potent and somewhat selective for the A1 receptor. None of the dihydroxyphenyl analogues are remarkably potent, but all are selective for the A1 receptor. 1,3-Dipropyl-8-(2-hydroxy-4-methoxyphenyl)xanthine is the most selective A1 antagonist of the analogues with a A1/A2 potency ratio of about 90.

A [3H]amine congener of 1,3-dipropyl-8-phenylxanthine. A new radioligand for A2 adenosine receptors of human platelets.[Pubmed:3009222]

FEBS Lett. 1986 Apr 21;199(2):269-74.

A xanthine amine congener (XAC), an amine-functionalized derivative of 1,3-Dipropyl-8-phenylxanthine, is an antagonist ligand for A2 adenosine receptors of human platelets. XAC inhibited 5'-N-ethylcarboxamidoadenosine (NECA)-induced stimulation of adenylate cyclase activity with a KB of 24 nM. [3H]XAC exhibits saturable, specific binding with a Kd of 12 nM and a Bmax of 1.1 pmol/mg protein at 37 degrees C. [3H]XAC binding in platelets is the first example of labeling of A2 adenosine receptors in which the potencies of adenosine agonists and antagonists in inhibiting binding are commensurate with their potencies at these receptors in functional studies. Furthermore, [3H]XAC is the first antagonist radioligand with high affinity at A2 adenosine receptors.

1,3-Dialkyl-8-(p-sulfophenyl)xanthines: potent water-soluble antagonists for A1- and A2-adenosine receptors.[Pubmed:2984420]

J Med Chem. 1985 Apr;28(4):487-92.

A series of 8-(substituted phenyl) derivatives of theophylline and other 1,3-dialkylxanthines were evaluated for potency and selectivity as antagonists at A1- and A2-adenosine receptors in brain tissue. Theophylline has a similar potency (Ki = 14 microM) at both A1 and A2 receptors. 8-Phenyltheophylline is 25-35-fold more potent as an adenosine receptor antagonist than theophylline, while 8-phenylcaffeine is only 2-3-fold more potent than caffeine. A p-hydroxyaryl substituent enhances the potency of 8-phenyltheophylline as an adenosine antagonist. p-Carboxy- and p-sulfoaryl substituents reduce potency of 8-phenyltheophylline, yielding water-soluble adenosine antagonists, which are some 2-5-fold more potent than theophylline at adenosine receptors. None of the 8-(substituted phenyl)theophyllines are particularly selective as antagonists toward A1- and A2-adenosine receptors. 1,3-Dipropyl-8-phenylxanthine represents a potent and somewhat selective A1-receptor antagonist about 23-fold more potent at A1 receptors than at A2 receptors. A p-hydroxyaryl substituent further enhances potency of the 1,3-Dipropyl-8-phenylxanthine at both A1 and A2 receptors. The 8-(2-amino-4-chlorophenyl)-1,3-dipropylxanthine is a very potent and selective antagonist for A1 receptors, being nearly 400-fold more potent at A1 than at A2 receptors. The water-soluble 8-(p-sulfophenyl)- and 8-(p-carboxyphenyl)-1,3-propylxanthines no longer exhibit marked selectivity. Both compounds are much more potent as adenosine antagonists than theophylline. The striking selectivity of 1-isoamyl-3-isobutylxanthine as an A1 antagonist is retained in the 8-phenyl derivative but is virtually lost in the 8-p-sulfophenyl derivative.