Meyer C, Neue B, Schepmann D, Yanagisawa S, Yamaguchi J, Würthwein EU, Itami K, Wünsch B. Improvement of σ1 receptor affinity by late-stage C-H-bond arylation of spirocyclic lactones.
Bioorg Med Chem 2013;
21:1844-56. [PMID:
23462714 DOI:
10.1016/j.bmc.2013.01.038]
[Citation(s) in RCA: 94] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Revised: 01/14/2013] [Accepted: 01/18/2013] [Indexed: 11/16/2022]
Abstract
The direct C-H-bond arylation of the complex spirocyclic lactones 13, 14, and 18 allows the introduction of diverse aryl moieties in the last step of the synthesis. A selective α-arylation of the thiophene moiety was performed with the catalytic system PdCl2/2,2'-bipyridyl/Ag2CO3, whereas the β-position of the thiophene ring was addressed by using the alternative catalytic system PdCl2/P[OCH(CF3)2]3/Ag2CO3. Due to electronic and steric reasons the arylation of the five-membered lactone 18 occurred in both α-positions providing 4'-mono-, 6'-mono- and 4',6'-diarylated thiophenes 22-26a-c. Compounds with an additional aryl moiety at the 'upper left (top)' position (1'-position of 13, 3'-position of 14, 4'-position of 18) showed increased σ1 affinity compared to the non-arylated parent compounds. A phenyl moiety at the 'left' position (2'-position in 20a) also increased the σ1 affinity but to a lower extent. A considerable reduction of σ1 affinity was observed after introducing an aryl moiety in 6'-position of 18, which might result from shielding the tertiary amine, which is crucial for interaction with the σ1 receptor. The discussion of the experimental results is supported by high-level quantum chemical DFT-calculations of the NBO-charges of 13 and 18 and the relative energies of the related arylated products.
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