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[摘要]：(N)-Methanocarba adenosine 5'-methyluronamides containing known A(3) AR (adenosine receptor)enhancing modifications, i.e., 2-(arylethynyl)adenine and N-6-methyl or N-6-(3-substituted-benzyl), were nanomolar full agonists of human (h) A(3)AR and highly selective (K-i similar to 0.6 nM, N-6-methyl 2-(halophenylethynyl) analogues 13 and 14). Combined 2-arylethynyl-N-6-3-chlorobenzyl substitutions preserved A(3)AR affinity/selectivity in the (N)-methanocarba series (e.g., 3,4-difluoro full agonist MRS5698 31, K-i 3 nM, human and mouse A(3)) better than that for ribosides. Polyaromatic 2-ethynyl N-6-3-chlorobenzyl analogues, such as potent linearly extended 2-p-biphenylethynyl MRS5679 34 (K-i hA(3) 3.1 nM; A(1), A(2A), inactive) and fluorescent 1-pyrene adduct MRS5704 35 (K-i hA(3) 68.3 nM), were conformationally rigid; receptor docking identified a large, mainly hydrophobic binding region. The vicinity of receptor-bound C2 groups was probed by homology modeling based on recent X-ray structure of an agonist-bound A(2A)AR, with a predicted helical rearrangement requiring an agonist-specific outward displacement of TM2 resembling opsin. Thus, the X-ray structure of related A(2A)AR is useful in guiding the design of new A(3)AR. agonists. |
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