The role of calcium in signal transduction relies on the precise spatial and temporal control of its concentration. The existing means to detect fluctuations in Ca2+ concentrations with adequate temporal and spatial resolution are limited. We introduce here a method to measure Ca2+ concentrations in defined locations in living cells that is based on linking the Ca2+-sensitive dye Indo-1 to SNAP-tag fusion proteins. Fluorescence spectroscopy of SNAP-Indo-1 conjugates in vitro showed that the conjugates retained the Ca2+-sensing ability of Indo-1. In a proof-of-principle experiment, local Ca2+ sensing was demonstrated in cultured primary muscle cells of mice expressing a nucleus-localized SNAP-tag fusion. Ca2+ concentrations inside nuclei of resting cells were measured by SEER (shifted excitation and emission ratioing) of confocal microscopic images of fluorescence. After permeabilizing the plasma membrane, changes in the bathing solution induced corresponding changes in nuclear [Ca2+] that were readily detected and used for a preliminary calibration of the technique. This work thus demonstrates the synthesis and application of SNAP-tag-based Ca2+ indicators that combine the spatial specificity of genetically encoded calcium indicators with the advantageous spectroscopic properties of synthetic indicators.

Neuritogenic natural products: The tricyclic diterpene cyrneine A featuring a hexatrienal unit was prepared synthetically for the first time by a Heck reaction, a carbene ring expansion, and a reductive carbonylation. The structure of the natural product was assigned by X‐ray crystal analysis of a synthetic sample.

The identification of all protein targets of a given drug or bioactive molecule within the human body is a prerequisite for an understanding of its beneficial and deleterious activities. Current approaches to reveal protein targets often fail to reveal physiologically relevant interactions. Here we review a recently introduced yeast-based approach for the identification of the binding partners of small molecules. We discuss the advantages and limitations of the approach using the clinically approved drug sulfasalazine as an example.

Synthetic studies towards the construction of the cyclopenta[a]indene fragment of the heptacyclic marine metabolite sporolide are reported based on a hypothetical biosynthesis. The key step of this biogenetic proposal includes a Bergman cyclization of an enediyne precursor. The enediyne target of this synthetic study was prepared by Sonogashira cross-coupling of two fragments, of which the cyclopentane fragment was prepared from cyclopentenone, Morita-Baylis-Hillman reaction, and enantioselective Sharpless dihydroxylation.

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