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This article explores the iridium-catalyzed asymmetric allylation of indoles using 1-alken-4-yn-3-ols. The researchers focus on optimizing the reaction by testing different additives and their impact on yield and enantioselectivity. The study provides valuable information on the synthesis of chiral polyacetylenic alcohols, which have important biological activities and potential applications in medicine. The reaction produces chiral allylated indoles and 1-alken-4-yn-3-ols with high enantioselectivities, demonstrating its compatibility with various functional groups. The findings also shed light on the absolute configuration of the products and have implications for the synthesis of chiral 1-alken-4-yn-3-ols. [Extracted from the article]

Genetically modified organisms (GMOs) are increasingly deployed at large scales and in open environments. Genetic biocontainment strategies are needed to prevent unintended proliferation of GMOs in natural ecosystems. Existing biocontainment methods are insufficient because they impose evolutionary pressure on the organism to eject the safeguard by spontaneous mutagenesis or horizontal gene transfer, or because they can be circumvented by environmentally available compounds. Here we computationally redesign essential enzymes in the first organism possessing an altered genetic code (Escherichia coli strain C32LAA) to confer metabolic dependence on non-standard amino acids for survival. The resulting GMOs cannot metabolically bypass their biocontainment mechanisms using known environmental compounds, and they exhibit unprecedented resistance to evolutionary escape through mutagenesis and horizontal gene transfer. This work provides a foundation for safer GMOs that are isolated from natural ecosystems by a reliance on synthetic metabolites., GMOs are rapidly being deployed for large-scale use in bioremediation, agriculture, bioenergy and therapeutics (1). In order to protect natural ecosystems and address public concern it is critical that the [...]

Two-photon absorption spectra and two-photon absorption cross sections of Cl-substituted diphenylacetylenes (ClDPAs) were investigated by optical-probing photoacoustic spectroscopy and quantum chemical calculations for the first time. The two-photon absorption spectra of ClDPAs exhibited intense two-photon absorption bands at around 480 nm, which are forbidden by one-photon absorption. The two-photon absorption cross sections σ(2) of o-, m-, and p-ClDPAs at 476 nm were determined to be 22 ± 1, 23 ± 1, and 38 ± 2 GM, respectively. Compared with diphenylacetylene (DPA) (27 GM at 472 nm), the σ(2) values of o- and m-ClDPAs were lower, while that of p-ClDPA was higher. Simulated two-photon absorption spectra using the TD-B3LYP/6-311+G(d,p) level of calculations within the Tamm-Dancoff approximation, based on the three-state model, well agreed with the experimental results. The difference in the σ(2) values of DPA and ClDPAs was responsible for those in the transition dipole moments between the intermediate and the final states. [ABSTRACT FROM AUTHOR]

Enzymes use substrate-binding energy both to promote ground-state association and to stabilize the reaction transition state selectively (1). The monomeric homing endonuclease I-AniI cleaves with high sequence specificity in the centre of a 20-base-pair (bp) DNA target site, with the amino (N)-terminal domain of the enzyme making extensive binding interactions with the left (-) side of the target site and the similarly structured carboxy (C)-terminal domain interacting with the right (+) side (2). Here we show that, despite the approximate twofold symmetry of the enzyme-DNA complex, there is almost complete segregation of interactions responsible for substrate binding to the (-) side of the interface and interactions responsible for transition-state stabilization to the (+) side. Although single base-pair substitutions throughout the entire DNA target site reduce catalytic efficiency, mutations in the (-) DNA half-site almost exclusively increase the dissociation constant ([K.sub.D]) and the Michaelis constant under single-turnover conditions ([K.sub.m.sup.*]), and those in the (+) half-site primarily decrease the turnover number ([k.sub.cat.sup.*]). The reduction of activity produced by mutations on the (-) side, but not mutations on the (+) side, can be suppressed by tethering the substrate to the endonuclease displayed on the surface of yeast. This dramatic asymmetry in the use of enzyme-substrate binding energy for catalysis has direct relevance to the redesign of endonucleases to cleave genomic target sites for gene therapy and other applications. Computationally redesigned enzymes that achieve new specificities on the (-) side do so by modulating [K.sub.M.sup.*], whereas redesigns with altered specificities on the (+) side modulate [k.sub.cat.sup.*]. Our results illustrate how classical enzymology and modern protein design can each inform the other., Enzymes use interactions with the substrate to promote catalysis both by bringing the substrate into close proximity and proper alignment with catalytic groups on the enzyme and by selectively stabilizing [...]

Homing endonucleases stimulate gene conversion by generating site-specific DNA double-strand breaks that are repaired by homologous recombination. These enzymes are potentially valuable tools for targeted gene correction and genome engineering. We have engineered a variant of the I-Anil homing endonuclease that nicks its cognate target site. This variant contains a mutation of a basic residue essential for proton transfer and solvent activation in one active site. The cleavage mechanism, DNA-binding affinity, and substrate specificity profile of the nickase are similar to the wildtype enzyme. I-Anil nickase stimulates targeted gene correction in human cells, in cis and in trans, at [approximately equal to]1/4 the efficiency of the wild-type enzyme. The development of sequence-specific nicking enzymes like the I-Anil nickase will facilitate comparative analyses of DNA repair and mutagenesis induced by single- or double-strand breaks. protein engineering I recombination I single strand breaks I gene therapy I gene repair