title: Synthesis of an azido-tagged low affinity ratiometric calcium sensor.
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 aKdof 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.
authors.affiliation: WestCHEM School of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Stuart T
authors.initials: ST
authors.lastname: Caldwell
authors.affiliation: WestCHEM School of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Cairns
authors.affiliation: Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.
authors.forename: Marnie
authors.initials: M
authors.lastname: Olson
authors.affiliation: Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.
authors.forename: Susan
authors.initials: S
authors.lastname: Chalmers
authors.affiliation: Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.
authors.forename: Mairi
authors.initials: M
authors.lastname: Sandison
authors.affiliation: 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.
authors.forename: William
authors.initials: W
authors.lastname: Mullen
authors.affiliation: Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.
authors.forename: John G
authors.initials: JG
authors.lastname: McCarron
authors.affiliation: WestCHEM School of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Hartley
keywords: BAPTA; Bioorthogonal; Calcium; Fluorescence; Thiohydantoin