title: Constitutional isomers of Reactive Blue 2 - selective P2Y-receptor antagonists?
abstract: The anthraquinone derivative Reactive Blue 2 (RB 2) is one of the most widely used P2-receptor antagonists, still claimed to be P2Y-selective. RB 2 is defined as a mixture of two constitutional isomers and commercially available in different identity and purity. A sample of RB 2, offered for sale by RBI, purchased from Biotrend, Köln, Germany, was chromatographically purified and identified by 1H- and 13C-NMR studies as a 35:65 mixture of the terminal ring F meta and para constitutional isomers. The two constitutional isomers of RB 2 were synthesised and tested alongside with the ortho isomer Cibacron Blue 3GA (CB 3GA) on contractions of the rat vas deferens (RVD) elicited by alpha,beta-methylene ATP (alpha,beta-MeATP), mediated by P2X(1)-receptors, and relaxations of the carbachol-precontracted guinea pig taenia coli elicited by adenosine 5'-O-(2-thiophosphate) (ADPbetaS), mediated by P2Y(1)-like-receptors. All compounds inhibited the alpha,beta-MeATP induced contraction of the RVD and the ADPbetaS induced relaxation of the carbachol precontracted guinea-pig taenia coli. The IC(50)-values at P2X(1)-R were 9.1 microM for CB 3GA, 28.4 microM for RB 2, 19.7 microM for RB 2 meta, and 35.5 microM for RB 2 para. The IC(50)-values at P2Y(1)-like-R were 17.4 microM for CB 3GA, 7.7 microM for RB 2, 12.0 microM for RB 2 meta, and 2.6 microM for RB 2 para. The results clearly show that neither RB 2 as a mixture nor the pure ortho and meta isomer are P2Y(1)-like- versus P2X(1)-selective antagonists. In contrast the pure para-isomer of RB 2 is a moderately P2Y(1)-like- versus P2X(1)-selective antagonist.
authors.affiliation: Chair of Pharmaceutical Chemistry, Albertstr. 25, 79104 i.Br., Freiburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Glänzel
authors.forename: Ralph
authors.initials: R
authors.lastname: Bültmann
authors.forename: Klaus
authors.initials: K
authors.lastname: Starke
authors.forename: August W
authors.initials: AW
authors.lastname: Frahm
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D003106:Colon / Q000187:drug effects; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D017208:Rats, Wistar; D013329:Structure-Activity Relationship; D013873:Thionucleotides / Q000494:pharmacology; D014227:Triazines / Q000737:chemistry*; D014649:Vas Deferens / Q000187:drug effects
chemical_list: D007202:Indicators and Reagents; D058919:Purinergic P2 Receptor Antagonists; D013873:Thionucleotides; D014227:Triazines; C030812:adenosine 5'-O-(2-thiodiphosphate); C012842:Cibacron Blue F 3GA; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate