Salimabromide: Unexpected Chemistry from the Obligate Marine Myxobacterium Enhygromxya salina

Marine myxobacteria (Enhygromyxa, Plesiocystis, Pseudoenhygromyxa, Haliangium) are phylogenetically distant from their terrestrial counterparts. Salimabromide is the first natural product from the Plesiocystis/Enhygromyxa clade of obligatory marine myxobacteria. Salimabromide has a new tetracyclic carbon skeleton, comprising a brominated benzene ring, a furano lactone residue, and a cyclohexane ring, bridged by a seven‐membered cyclic moiety. The absolute configuration was deduced from experimental and calculated CD data. Salimabromide revealed antibiotic activity towards Arthrobacter cristallopoietes.     

New acid/base salts as co‐catalysts for the organocatalyzed ring opening polymerization of lactide

(R)‐(+)‐binaphathyl‐diyl hydrogen phosphate (BNPH)/ diazabicyclo[5.4.0]undec‐7‐ene (DBU) and (1R)‐(?)?10‐camphorsulfonic acid (CSA)/4‐dimethylaminopyridine (DMAP) acid–base salts were synthesized and assessed for the ring‐opening polymerization of rac‐lactide. They were found to be inactive toward the polymerization in the presence of a protic initiator. When used in combination with a base such as DBU or DMAP and a protic initiator, these acid/base conjugates led to well‐controlled polymerization in mild conditions (D_M < 1.1 in all cases). With DBU, the presence of the salt was found to lead to narrower molecular weight distributions than those obtained using the base alone, and to prevent undesirable transesterification reactions occurring at the end of the reaction. An increase in activity was observed using the salts in combination with DMAP as compared with DMAP alone, together with an improvement of the control over the molecular weight. The results were discussed on the basis of ¹H nuclear magnetic resonance analyzes including acid/base equilibria involving the use of two different bases. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 659–664     

Vacuum-UV and Low-Energy Electron-Induced DNA Strand Breaks – Influence of the DNA Sequence and Substrate

DNA is effectively damaged by radiation, which can on the one hand lead to cancer and is on the other hand directly exploited in the treatment of tumor tissue. DNA strand breaks are already induced by photons having an energy below the ionization energy of DNA. At high photon energies, most of the DNA strand breaks are induced by low-energy secondary electrons. In the present study we quantified photon and electron induced DNA strand breaks in four different 12mer oligonucleotides. They are irradiated directly with 8.44 eV vacuum ultraviolet (VUV) photons and 8.8 eV low energy electrons (LEE). By using Si instead of VUV transparent CaF₂ as a substrate the VUV exposure leads to an additional release of LEEs, which have a maximum energy of 3.6 eV and can significantly enhance strand break cross sections. Atomic force microscopy is used to visualize strand breaks on DNA origami platforms and to determine absolute values for the strand break cross sections. Upon irradiation with 8.44 eV photons all the investigated sequences show very similar strand break cross sections in the range of 1.7–2.3×10⁻¹⁶ cm². The strand break cross sections for LEE irradiation at 8.8 eV are one to two orders of magnitude larger than the ones for VUV photons, and a slight sequence dependence is observed. The sequence dependence is even more pronounced for LEEs with energies <3.6 eV. The present results help to assess DNA damage by photons and electrons close to the ionization threshold.     

Xylochemical Synthesis and Biological Evaluation of Shancigusin C and Bletistrin G

The biological activities of shancigusin C (1) and bletistrin G (2), natural products isolated from orchids, are reported along with their first total syntheses. The total synthesis of shancigusin C (1) was conducted by employing the Perkin reaction to forge the central stilbene core, whereas the synthesis of bletistrin G (2) was achieved by the Wittig olefination followed by several regioselective aromatic substitution reactions. Both syntheses were completed by applying only renewable starting materials according to the principles of xylochemistry. The cytotoxic properties of shancigusin C (1) and bletistrin G (2) against tumor cells suggest suitability as a starting point for further structural variation.