Synthesis of Strophasterol A Guided by a Proposed Biosynthesis and Innate Reactivity

The synthesis of strophasterol A, a moderator of endoplasmatic reticulum (ER) stress in Alzheimer's disease, and the first member of a structurally unprecedented class of secosterols, was achieved through the implementation of a key step of its proposed biosynthesis and two C?H oxidations. Analysis of the innate reactivity of the intermediates enabled the identification of a novel way to prepare an α‐chloro‐γ‐hydroxy‐δ‐keto enone, as well as its vinylogous α‐ketol rearrangement to a δ‐keto carboxylic acid.     

Heat‐Flow‐Driven Oligonucleotide Gelation Separates Single‐Base Differences

DNA phase transitions are often induced by the addition of condensation agents or by dry concentration. Herein, we show that the non‐equilibrium setting of a moderate heat flow across a water‐filled chamber separates and gelates DNA strands with single‐base resolution. A dilute mix of DNA with two slightly different gel‐forming sequences separates into sequence‐pure hydrogels under constant physiological solvent conditions. A single base change in a 36 mer DNA inhibits gelation. Only sequences with the ability to form longer strands are concentrated, further elongated, and finally gelated by length‐dependent thermal trapping. No condensation agents, such as multivalent ions, were added. Equilibrium aggregates from dry concentration did not show any sequence separation. RNA is expected to behave identically owing to its equal thermophoretic properties. The highly sequence‐specific phase transition points towards new possibilities for non‐equilibrium origins of life.     

Access to Pyrazolidin‐3,5‐diones through Anodic N–N Bond Formation

Pyrazolidin‐3,5‐diones are important motifs in heterocyclic chemistry and are of high interest for pharmaceutical applications. In classic organic synthesis, the hydrazinic moiety is installed through condensation using the corresponding hydrazine building blocks. However, most N,N′‐diaryl hydrazines are toxic and require upstream preparation owing to their low commercial availability. We present an alternative and sustainable synthetic approach to pyrazolidin‐3,5‐diones that employs readily accessible dianilides as precursors, which are anodically converted to furnish the N?N bond. The electroconversion is conducted in a simple undivided cell under constant‐current conditions.     

On a theorem of Rigby

Let \({\Delta = BAG(2, q)}\) denote the classical biaffine plane of order q, that is, the symmetric \({((q^2 - 1)_q)}\) configuration obtained from the classical affine plane \({\Sigma = AG(2, q)}\) of order q by omitting a point of \({\Sigma}\) together with all lines through this point. Now let \({q \geq 4}\) be a power of a prime p and assume that \({\Delta}\) admits an embedding into the projective plane \({\Pi = PG(2, F)}\), where F is a (not necessarily commutative) field. Then this embedding extends to a projective subplane \({\Pi_0 \cong PG(2, q)}\) of \({\Pi}\); in particular, F has characteristic p. Consequently, \({BAG(2, q)}\) with \({q\geq 4}\) admits an embedding into \({PG(2, q')}\) if only if q′ is a power of q. This strengthens a result of Rigby (Canad J Math 17:977–1009, 1965) in a special case while simultaneously providing a more elegant proof.     

Regioselective Functionalization of 3‐Hydroxy‐pyridine Carboxylates by Neighboring Group Assistance

Regioselective hydrolysis, transesterification, and aminolysis of unactivated, highly substituted pyridine esters were realized under mild conditions by employing neighboring group assisted catalysis. Excellent yields were achieved without active removal of the alcohol byproduct. Regioselective aminolysis had a considerable substrate scope ([hetero]aryl, alkyl and amino acid). A mechanism involving assistance by the deprotonated phenolic OH‐group is suggested for hydrolysis and transesterification.     

Guiding the location of nanoparticles into vesicular structures: a morphological study

The present paper investigates the selective incorporation of preformed nanoparticles (hydrophobic Au-NP (2 nm); hydrophilic Au-NP (12 nm); hydrophobic CdSe-NP (1.9 nm); retrovirus-particles (approximately 30 nm)) into the interface of lipid vesicles and polymersomes via TEM and DLS investigations. Lipid membranes were made from N,N-dimethyl-N,N-dioctadecylammonium bromide (DODAB), di-oleoyl-phosphatidylcholine (DOPC), whereas polymersome-membranes were fabricated from the diblock copolymer poly-(butadiene-block-ethylenoxide). Stabilization of the final structures was achieved via sol/gel processes at the outside of the membranes, thus stabilizing the structure by a silicate shell. Whereas hydrophobic Au-NPs can be successfully embedded into the polymersome- and lipid-vesicle membranes, hydrophilic nanoparticles were found evenly distributed in the inner- and outer compartments of the vesicles and polymersomes. Significant effects such as size reduction, selective enrichment of all nanoparticles within only few polymersomes as well as budding effects of larger entities (i.e., viral particles) are described.     

Perfluoroalkyl(dithiocarbamato) tellurium(II) compounds

[NMe(4)][R(f)Te(SC(S)NR(2))(2)] derivatives are selectively formed by the oxidation of [NMe(4)]TeR(f) (R(f) = CF(3), C(2)F(5)) with [R(2)NC(S)S](2) (NR(2) = NEt(2), NBz(2), N(CH(2))(4)) in almost quantitative yields. An alternative route to obtain the dithiocarbamato complex anions offer reactions of Te[SC(S)NR(2)](2) (NR(2) = NEt(2), NBz(2)) with equimolar amounts of Me(3)SiR(f) and [NMe(4)]F. Some of the derivatives were recrystallized with bulky cations in order to determine the crystal structures. Structural elucidation by diffraction methods exhibit the structural feature of a distorted pentagonal planar environment (resembling "butterflies") around the tellurium centres. The carbamato tellurates can be transferred easily into the neutral derivatives, R(f)TeSC(S)NR(2), upon treatment with Ag[BF(4)]. In solution they equilibrate with Te(2)(R(f))(2) and [R(2)NC(S)S](2) and finally are transformed into Te(R(f))(2), Te[SC(S)NR(2)](2), and Te[SC(S)NR(2)](4), respectively. All compounds are fully characterized by NMR spectroscopic methods ((1)H, (13)C, (19)F, (125)Te). Additionally, synthesis and characterization of the hitherto unknown derivative [NMe(4)]TeC(2)F(5) are described.     

The Structure of Tris(trifluoromethyl)tellurium Fluoride Dimethylformamide, $\rm [Te(CF_{3})_{3} \times DMF(\mu-F)]{\infty}$

represents the first structurally characterized example of a trifluoromethyl main group element compound with more than 8‐N (where N is the main group number) perfluoroalkyl groups and also the first fluoro(triorgano)tellurium derivative. Its polymeric nature is caused by asymmetric bridging fluorine atoms forming infinite chains.