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1.  Adenosine analogs with covalently attached lipids have enhanced potency at A1-adenosine receptors 
FEBS letters  1987;225(0):97-102.
Chemically functionalized congeners of N6-phenyladenosine and I ,3-dipropyl-8-phenylxanthine have been covalently coupled to fatty acids, diglyceridcs, and a phospholipid. The lipid-drug conjugates inhibit R-[3H]-phenylisopropyladenosinc binding to A1-adcnosine receptors in rat cerebral cortex membranes. A xanthinepbosphatidylethanolaminc conjugate bound with a K1 value of 19 nM. Various xanthine esters of low potency are potential prod rugs. Amides of an adenosine amine congener (ADA C) with 18-carbon fatty acids exhibited Ki values at A1-adenosine receptors of 70 pM, representing a 130-fold enhancement over the affinity of the corresponding acetyl amide. The very high affinity of adenosine-lipid conjugates may be due to stabilization of these adducts in the phospholipid microenvironment of the receptor protein.
PMCID: PMC4287258  PMID: 3691809
Lipid; Adenosine receptor; Xanthine; Adenosine derivative; Lipid-drug conjugate; Prodrug
2.  Sulfur-Containing 1,3-Dialkylxanthine Derivatives as Selective Antagonists at A1-Adenosine Receptors 
Journal of medicinal chemistry  1989;32(8):1873-1879.
Sulfur-containing analogues of 8-substituted xanthines were prepared in an effort to increase selectivity or potency as antagonists at adenosine receptors. Either cyclopentyl or various aryl substituents were utilized at the 8-position, because of the association of these groups with high potency at A1-adenosine receptors. Sulfur was incorporated on the purine ring at positions 2 and/or 6, in the 8-position substituent in the form of 2- or 3-thienyl groups, or via thienyl groups separated from an 8-aryl substituent through an amide-containing chain. The feasibility of using the thienyl group as a prosthetic group for selective iodination via its Hg2+ derivative was explored. Receptor selectivity was determined in binding assays using membrane homogenates from rat cortex [[3H]-N6-(phenylisopropyl) adenosine as radioligand] or striatum [[3H]-5′-(N-ethylcarbamoyl)adenosine as radioligand] for A1- and A2-adenosine receptors, respectively. Generally, 2-thio-8-cycloalkylxanthines were at least as A1 selective as the corresponding oxygen analogue. 2-Thio-8-aryl derivatives tended to be more potent at A2 receptors than the oxygen analogue. 8-[4-[(Carboxymethyl)oxy]phenyl]-1,3-dipropyl-2-thioxanthine ethyl ester was >740-fold A1 selective.
PMCID: PMC3479653  PMID: 2754711
3.  Adenosine Receptor Prodrugs: Towards Kidney-Selective Dialkylxanthines 
XAC (xanthine amine congener, 8-{4-[(2-aminoethyl)-aminocarbonylmethyloxy]phenyl}-1,3-dipropylxanthine is a potent adenosine antagonist that reverses the reduction in urine flow, sodium excretion and heart rate produced by the adenosine agonist, N6-cyclohexyladenosine. New derivatives of XAC in which the primary amino group has been condensed to the γ-carboxyl group of glutamic acid have been synthesized as prodrugs. These amino acid-XAC conjugates, which are considerably less potent than XAC in competitive binding assays at A1-adenosine receptors, are designed for selective enzymatic activation in the kidneys. The γ-glutamyl xanthine derivatives are substrates for γ-glutamyl transferase (EC 2.3.2.2) to generate an amine-functionalized xanthine. N-acetyl-γ-L-glutamyl-XAC is not active in vivo, consistent with inability of renal acylase (EC 3.5.1.14) to hydrolyze the acetyl group, a prerequisite step for the production of XAC from this molecule. The xanthine derivatives, γ-L-glutamyl-XAC and γ-L-glutamyl-γ-L-glutamyl-XAC are metabolized to XAC and produce a diuresis in vivo.
PMCID: PMC3476460  PMID: 2746513
4.  Electrophilic Derivatives of Purines as Irreversible Inhibitors of A1 Adenosine Receptors 
Journal of medicinal chemistry  1989;32(5):1043-1051.
Functionalized congeners derived from 1,3-dipropyl-8-phenylxanthine and from N6-phenyladenosine were derivatized to contain electrophilic groups (isothiocyanate, N-hydroxysuccinimide ester, maleimide, sulfonyl chloride, or α-haloacyl group) capable of reaction with nucleophiles on biopolymers. The goal was to inhibit chemically the A1 adenosine receptor by using reactive agonist and antagonist ligands. Some of the electrophilic derivatives were synthesized through acylation of amine-functionalized congeners using hetero- or homobifunctional reagents available for protein cross-linking. The affinity for A1 adenosine receptors was evaluated in competitive binding assays by using rat and bovine brain membranes. Several xanthine and adenosine thiourea derivatives prepared from 1,3- and l,4-phenylene diisothiocyanate (DITC) were potent irreversible inhibitors of adenosine receptors. Derivatives of m-DITC, at concentrations between 10 and 500 nM, irreversibly eliminated binding at 90% of the A1-receptor sites. Receptor affinity of both xanthine and adenosine derivatives containing distal phenylthiourea substituents was diminished by electron-donating groups on the ring.
PMCID: PMC3442263  PMID: 2709373

Results 1-4 (4)