Discovery of a cyclic 6 + 6 hexamer of d-biotin and formaldehydeElectronic supplementary information (ESI) available: Experimental data and characterisation data: synthetic protocols, NMR titration data, single crystal X-ray crystallography data. CCDC 994261 and 988132. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4sc00990h

The discovery of receptors using templated synthesis enables the selection of strong receptors from complex mixtures. In this contribution we describe a study of the condensation of d -biotin and formaldehyde in acidic water. We have discovered that halide anions template the formation of a single isomer of a 6 + 6 macrocycle. The macrocycle (biotin[6]uril) is water-soluble, chiral and binds halide anions (iodide, bromide and chloride) with selectivity for iodide in water, and it can be isolated on a gram scale in a one-pot reaction in 63% yield. The discovery of receptors using templated synthesis enables the selection of strong receptors from complex mixtures.