Polymeric Encapsulation of Novel Homoleptic Bis(dipyrrinato) Zinc(II) Complexes with Long Lifetimes for Applications as Photodynamic Therapy Photosensitisers

The use of photodynamic therapy (PDT) to treat cancer has received increasing attention over the last years. However, the clinically used photosensitisers (PSs) have some limitations that include poor aqueous solubility, hepatotoxicity, photobleaching, aggregation, and slow clearance from the body, so the design of new classes of PSs is of great interest. We present the use of bis(dipyrrinato)zinc(II) complexes with exceptionally long lifetimes as efficient PDT PSs. Based on the heavy‐atom effect, intersystem crossing of these complexes changes the excited state from singlet to a triplet state, thereby enabling singlet oxygen generation. To overcome the limitation of quenching effects in water and improve water solubility, the lead compound 3 was encapsulated in a polymer matrix. It showed impressive phototoxicity upon irradiation at 500 nm in various monolayer cancer cells as well as 3D multicellular tumour spheroids, without observed dark toxicity.     

What is the role of acid–acid interactions in asymmetric phosphoric acid organocatalysis? A detailed mechanistic study using interlocked and non-interlocked catalysts

Organocatalysis has revolutionized asymmetric synthesis. However, the supramolecular interactions of organocatalysts in solution are often neglected, although the formation of catalyst aggregates can have a strong impact on the catalytic reaction. For phosphoric acid based organocatalysts, we have now established that catalyst–catalyst interactions can be suppressed by using macrocyclic catalysts, which react predominantly in a monomeric fashion, while they can be favored by integration into a bifunctional catenane, which reacts mainly as phosphoric acid dimers. For acyclic phosphoric acids, we found a strongly concentration dependent behavior, involving both monomeric and dimeric catalytic pathways. Based on a detailed experimental analysis, DFT-calculations and direct NMR-based observation of the catalyst aggregates, we could demonstrate that intermolecular acid–acid interactions have a drastic influence on the reaction rate and stereoselectivity of asymmetric transfer-hydrogenation catalyzed by chiral phosphoric acids.

Supramolecular acid–acid interactions lead to competing monomeric and dimeric pathways in phosphoric acid catalysis – so that stereoselectivities depend on catalyst concentration.     

Stereochemistry of intramolecular Diels-Alder furan (IMDAF) reactions of furyl-substituted chiral ethanolamides

This paper describes the stereoselective outcome of the intramolecular Diels-Alder furan (IMDAF) reaction of substituted (2S,3S)-ethanolamides 9-13, which were synthesised from a furyl substituted cyanohydrin. The latter was obtained from 2-furaldehyde with high enantioselectivity by an oxynitrilase catalysed addition of hydrogen cyanide. The stereochemistry of the IMDAF products was shown to be dependent on the size of the ethanolamide substituents R. Small substituents (H, Me, CN) gave exclusively exo-cycloaddition, whereas more bulky ones (Ph, Et) gave both evo- and endo-addition, the larger phenyl substituent giving a high endo-exo-ratio.     

Penicillamin-Komplexe des Nickels,Chroms und Molybdäns — Strukturelle Besonderheiten und biologische/medizinische Relevanz

Penicillamine Complexes of Nickel, Chromium, and Molybdenum — Structural Particularity and Biological/Medical Relevance The compounds Tl₂[Ni^II(H₂O)₆][Ni^II(D-pen)(L-pen)]₂[Ni^II(SCN)₂(H₂O)₄] 1 , Tl[Ni^II(D-pen)₂H] · H₂O 2 , Tl[Cr^III(D-pen)₂] 3 , and Na₂[MoO₄(pen)₂] · 3 CH₃OH · 3 H₂O 4 have been prepared by the reaction of nickel nitrate (for 1 ), nickel acetate (for 2 ), potassium chromate (for 3 ), and sodium molybdate (for 4 ) with D- and D, L-penicillamine, respectively. They were characterized by single-crystal X-ray structure analysis and other physical methods. Whereas penicillamine acts as a bidentate (N, S)-ligand in 1 and 2 , Cr^III (in 3 ), and Mo^V (in 4 ) are coordinated to the three ligand atoms N, O, and S. The presence of three different types of Ni^II-complexes a cationic, a neutral, and an anionic one in 1 is remarkable. For crystal data see Inhaltsübersicht.     

Über die Entstehung von Oligoanthrylen bei der milden Sulfonierung von Anthracen

The sulfonation of anthracene yields a variety of products and byproducts by different reaction paths depending on the reaction conditions. While trying to reduce the number of products formed by sulfonation under mild conditions, a new reaction was found: under certain sulfonation conditions anthracene is not sulfonated but reacts to form oligoanthrylenes. The highest average molecular weight of a fraction, insoluble in benzene, is about 3,000.     

Asymmetric Synthesis of Densely Functionalized Medium‐Ring Carbocycles and Lactones through Modular Assembly and Ring‐Closing Metathesis of Sulfoximine‐Substituted Trienes and Dienynes

An asymmetric synthesis of densely functionalized 7–11‐membered carbocycles and 9–11‐membered lactones has been developed. Its key steps are a modular assembly of sulfoximine‐substituted C‐ and O‐tethered trienes and C‐tethered dienynes and their Ru‐catalyzed ring‐closing diene and enyne metathesis (RCDEM and RCEYM). The synthesis of the C‐tethered trienes and dienynes includes the following steps: 1) hydroxyalkylation of enantiomerically pure titanated allylic sulfoximines with unsaturated aldehydes, 2) α‐lithiation of alkenylsulfoximines, 3) alkylation, hydroxy‐alkylation, formylation, and acylation of α‐lithioalkenylsulfoximines, and 4) addition of Grignard reagents to α‐formyl(acyl)alkenylsulfoximines. The sulfoximine group provided for high asymmetric induction in steps 1) and 4). RCDEM of the sulfoximine‐substituted trienes with the second‐generation Ru catalyst stereoselectively afforded the corresponding functionalized 7–11‐membered carbocyles. RCDEM of diastereomeric silyloxy‐substituted 1,6,12‐trienes revealed an interesting difference in reactivity. While the (R)‐diastereomer gave the 11‐membered carbocyle, the (S)‐diastereomer delivered in a cascade of cross metathesis and RCDEM 22‐membered macrocycles. RCDEM of cyclic trienes furnished bicyclic carbocycles with a bicyclo[7.4.0]tridecane and bicyclo[9.4.0]pentadecane skeleton. Selective transformations of the sulfoximine‐ and bissilyloxy‐substituted carbocycles were performed including deprotection, cross‐coupling reaction and reduction of the sulfoximine moiety. Esterification of a sulfoximine‐substituted homoallylic alcohol with unsaturated carboxylic acids gave the O‐tethered trienes, RCDEM of which yielded the sulfoximine‐substituted 9–11‐membered lactones. RCEYM of a sulfoximine‐substituted 1,7‐dien‐10‐yne showed an unprecedented dichotomy in ring formation depending on the Ru catalyst. While the second‐generation Ru catalyst gave the 9‐membered exo 1,3‐dienyl carbocycle, the first‐generation Ru catalyst furnished a truncated 9‐membered 1,3‐dieny carbocycle having one CH₂ unit less than the dienyne.     

Synthesis of (−)‐Hebelophyllene E: An Entry to Geminal Dimethyl‐Cyclobutanes by [2+2] Cycloaddition of Alkenes and Allenoates

The first synthesis of hebelophyllene E is presented, along with assignment of its previously unknown relative configuration through synthesis of epi‐ent‐hebelophyllene E. Development of a catalytic enantioselective [2+2] cycloaddition of alkenes and allenoates provides access to the required chiral geminal dimethylcyclobutanes. Key to its success is the identification of a novel oxazaborolidine catalyst which promotes the cycloaddition in high enantioselectivities with good functional‐group tolerance (9 examples, up to 97:3 e.r.). Thus, a late‐stage cycloaddition using a fully functionalized alkene, followed by a diastereoselective reduction allows a concise entry to this class of natural products.     

Measurement of the flexibility of wet cellulose fibres using atomic force microscopy

Flexibility and modulus of elasticity data for two types of wet cellulose fibres using a direct force–displacement method by means of AFM are reported for never dried wet fibres immersed in water. The flexibilities for the bleached softwood kraft pulp (BSW) fibres are in the range of 4–38 × 10¹² N^?1 m^?2 while the flexibilities for the thermomechanical pulp (TMP) fibres are about one order of magnitude lower. For BSW the modulus of elasticity ranges from 1 to 12 MPa and for TMP between 15–190 MPa. These data are lower than most other available pulp fibre data and comparable to a soft rubber band. Reasons for the difference can be that our measurements with a direct method were performed using never dried fibres immersed in water while other groups have employed indirect methods using pulp with different treatments.