Synthesis of an azido-tagged low affinity ratiometric calcium sensor

Stuart T Caldwell; Andrew G Cairns; Marnie Olson; Susan Chalmers; Mairi Sandison; William Mullen; John G McCarron; Richard C Hartley

doi:10.1016/j.tet.2015.10.052

Synthesis of an azido-tagged low affinity ratiometric calcium sensor

Tetrahedron. 2015 Dec 23;71(51):9571-9578. doi: 10.1016/j.tet.2015.10.052.

Authors

Stuart T Caldwell¹, Andrew G Cairns¹, Marnie Olson², Susan Chalmers², Mairi Sandison², William Mullen³, John G McCarron², Richard C Hartley¹

Affiliations

¹ WestCHEM School of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK.
² Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.
³ BHF Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.

Abstract

Changes in high localised concentrations of Ca²⁺ ions are fundamental to cell signalling. The synthesis of a dual excitation, ratiometric calcium ion sensor with a K_d of 90 μM, is described. It is tagged with an azido group for bioconjugation, and absorbs in the blue/green and emits in the red region of the visible spectrum with a large Stokes shift. The binding modulating nitro group is introduced to the BAPTA core prior to construction of a benzofuran-2-yl carboxaldehyde by an allylation-oxidation-cyclisation sequence, which is followed by condensation with an azido-tagged thiohydantoin. The thiohydantoin unit has to be protected with an acetoxymethyl (AM) caging group to allow CuAAC click reaction and incorporation of the KDEL peptide endoplasmic reticulum (ER) retention sequence.

Keywords: BAPTA; Bioorthogonal; Calcium; Fluorescence; Thiohydantoin.

Abstract

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