Some rare indigo derivatives have been known for a long time to be photochromic upon irradiation with red light, which should be advantageous for many applications. However, the absence of strategies to tune their thermal half-lives by modular molecular design as well as the lack of proper synthetic methods to prepare a variety of such molecules from the parent indigo dye have so far precluded their use. In this work, several synthetic protocols for N-functionalization have been developed, and a variety of N-alkyl and N-aryl indigo derivatives have been prepared. By installation of electron-withdrawing substituents on the N-aryl moieties, the thermal stability of the Z-isomers could be enhanced while maintaining the advantageous photoswitching properties upon irradiation with red light (660 nm LED). Both experimental data and computational results suggest that the ability to tune thermal stability without affecting the dyes' absorption maxima originates from the twisted geometry of the N-aryl groups. The new indigo photoswitches reported are expected to have a large impact on the development of optical methods and applications in both life and material sciences.

Combining bioengineering with chemical synthesis has enabled an efficient method for producing Δ7-dafachronic acid, a steroidal hormone associated with nematode germline longevity. Saccharomyces cerevisiae was engineered to produce 7,24-cholestadienol, a convenient starting material for a four-step synthesis of Δ7-dafachronic acid.

Mixed Bioengineering-Chemical Synthesis Approach for the Efficient Preparation of 7-Dafachronic Acid. -The steroidal hormone 7-dafachronic acid is prepared in 4 steps, including an olefin metathesis. The starting material 7,24-cholastdienol is produced by saccharomyces cerevisiae. -(KINZURIK, M. I.; HRISTOV, L. V.; MATSUDA, S. P. T.; BALL*, Z. T.; Org. Lett. 16 (2014) 8, 2188-2191, http://dx.doi.org/10.1021/ol5006642 ; Dep. Chem., Rice Univ., Houston, TX 77005, USA; Eng.) -F. Berndt 42-222