title: Synthesis and biological evaluation of disubstituted N6-cyclopentyladenine analogues: the search for a neutral antagonist with high affinity for the adenosine A1 receptor.
abstract: Novel 3,8- and 8,9-disubstituted N(6)-cyclopentyladenine derivatives were synthesised in moderate overall yield from 6-chloropurine. The derivatives were made in an attempt to find a new neutral antagonist with high affinity for adenosine A(1) receptors. N(6)-Cyclopentyl-9-methyladenine (N-0840) was used as a lead compound. Binding affinities of the new analogues were determined for human adenosine A(1) and A(3) receptors. Their intrinsic activity was assessed in [35S]GTPgammaS binding experiments. Elongation of the 9-methyl of N-0840 to a 9-propyl substituent was very well tolerated. A 9-benzyl group, on the other hand, caused a decrease in adenosine A(1) receptor affinity. Next, the 8-position was examined in detail, and affinity was increased with appropriate substitution. Most derivatives were A(1)-selective and 20 of the new compounds (6-9, 15-21, 23-26, 28, 31, 33, 35, and 36) had higher adenosine A(1) receptor affinity than the reference substance, N-0840. Compound 31 (N(6)-cyclopentyl-8-(N-methylisopropylamino)-9-methyladenine, LUF 5608) had the highest adenosine A(1) receptor affinity, 7.7 nM. In the [35S]GTPgammaS binding experiments, derivatives 5, 14, 22, 23, 25, 26, 33 and 34 did not significantly change basal [35S]GTPgammaS binding, thus behaving as neutral antagonists. Moreover, four of these compounds (23, 25, 26, and 33) displayed a 4- to 10-fold increased adenosine A(1) receptor affinity (75-206 nM) compared to N-0840 (852 nM). In summary, we synthesised a range of N-0840 analogues with higher affinity for adenosine A(1) receptors. In addition, four new derivatives, LUF 5666 (23), LUF 5668 (25), LUF 5669 (26) and LUF 5674 (33), behaved as neutral antagonists when tested in [35S]GTPgammaS binding studies. Thus, these compounds have improved characteristics as neutral adenosine A(1) receptor antagonists.
authors.affiliation: Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Leiden University, PO Box 9502, 2300 RA, Leiden, The Netherlands.
authors.forename: Rianne A F
authors.initials: RA
authors.lastname: de Ligt
authors.forename: Pieter A M
authors.initials: PA
authors.lastname: van der Klein
authors.forename: Jacobien K
authors.initials: JK
authors.lastname: von Frijtag Drabbe Künzel
authors.forename: Anna
authors.initials: A
authors.lastname: Lorenzen
authors.forename: Fatna
authors.initials: F
authors.lastname: Ait El Maate
authors.forename: Shelly
authors.initials: S
authors.lastname: Fujikawa
authors.forename: Rosemarijn
authors.initials: R
authors.lastname: van Westhoven
authors.forename: Thijs
authors.initials: T
authors.lastname: van den Hoven
authors.forename: Johannes
authors.initials: J
authors.lastname: Brussee
authors.forename: Ad P
authors.initials: AP
authors.lastname: IJzerman
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000494:pharmacology; D058916:Adenosine A1 Receptor Antagonists; D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D004353:Drug Evaluation, Preclinical / Q000379:methods; D006801:Humans; D043682:Receptor, Adenosine A1 / Q000502:physiology
chemical_list: D058916:Adenosine A1 Receptor Antagonists; D043682:Receptor, Adenosine A1; C048599:N(6)-cyclopentyladenosine; D000225:Adenine; D000241:Adenosine