The Walden memorial at the Technical University in Riga is pictured in the frontispiece to mark the recent centennial of the Walden inversion. This is a rare public monument to key events from the first era of exploration in stereocontrolled synthesis, and may be the only such monument to use the language of organic chemistry expressed at the molecular level. The reaction of racemic substrates with chiral nucleophiles is one of many methods currently known to achieve kinetic resolution, a phenomenon that ranks as the oldest and most general approach for the synthesis of highly enantioenriched substances. The first nonenzymatic kinetic resolutions as well as the original forms of the Walden inversion were studied in the 1890s. All of these investigations were conducted within the first generation following the demonstration that carbon is tetrahedral, and provided abundant evidence that the principles and importance of enantiocontrolled syntheses were understood. However, a reliable, rapid technique to quantify results and guide the optimization process was still lacking. Many decades passed before this problem was solved by the advent of HPLC and GLPC assays on chiral supports, which stimulated explosive growth in the synthesis of nonracemic substances by kinetic resolution. The Walden monument is accessible to passers-by for hands-on inspection as well as for contemplation and learning. In a similar way, kinetic resolution is experimentally accessible and can be thought-provoking at several levels. We follow the story of kinetic resolution from the early discoveries through fascinating historical milestones and conceptual developments, and close with a focus on modern techniques that maximize efficiency.

Das im Vortitel gezeigte Walden‐Denkmal auf dem Campus der Technischen Universität Riga ist sicher eines der wenigen öffentlichen Monumente, die Schlüsselereignisse aus der Anfangszeit der stereokontrollierten Synthese thematisieren und vielleicht das einzige, das die “molekulare Sprache” der organischen Chemie gebraucht. Die ersten nichtenzymatischen kinetischen Racematspaltungen wurden, ebenso wie die ursprünglichen Varianten der Walden‐Umkehr, in den 1890er Jahren untersucht – also noch in der ersten Forschergeneration nach Entdeckung der tetraedrischen Natur des Kohlenstoffs. Aus diesen frühen Arbeiten ist abzulesen, dass die Prinzipien und die Bedeutung enantiokontrollierter Synthesen bereits gut verstanden waren. Was noch fehlte war eine verlässliche und schnelle Methode zur Quantifizierung der Ergebnisse und zur Optimierung der Experimente. Viele Jahrzehnte sollten vergehen, bis das Problem mit Einführung von HPLC‐ und GPLC‐Testreihen auf chiralen Trägern gelöst wurde. Das Walden‐Denkmal lädt den Vorübergehenden zur spielerischen Betrachtung ein – auf ähnliche Weise, wie auch die kinetische Racematspaltung zum Experimentieren einlädt. Dieser Aufsatz verfolgt den Verlauf der Geschichte angefangen von den ersten Entdeckungen über die faszinierenden historischen Meilensteine und konzeptionellen Entwicklungen und schließt mit einem Blick auf moderne Techniken zur Effizienzmaximierung.

To obtain new crystal forms with altered physicochemical properties and to get insight into the driving forces guiding cocrystallization, we performed experimental and in silico screening of pentoxifylline with 11 pharmaceutically acceptable organic acids. Neat grinding, liquid-assisted grinding, and slow solvent evaporation were used to obtain cocrystals of pentoxifylline. The free energy of experimental and hypothetical crystal structures have been calculated using the FlexCryst program. Three cocrystals of pentoxifylline with aspirin, salicylic acid, and benzoic acid in a 1:1 molar ratio have been obtained and characterized by physical methods. The experimental and in silico results were found to match very well. Strong correlation between melting points of pentoxifylline cocrystals and coformers has been detected. A significant decrease in solubility of pentoxifylline cocrystals as compared to pure pentoxifylline was observed.

This paper deals with studies of the content of some antioxidants in barley (Hordeum vulgare L.), which is one of the major cereal species with extensive application in food products with increased nutritional value. We studied the effect of genotype and environment on the content of α-tocopherol and total polyphenol content in grain and grain oil and phenolic compounds in grain of two covered and four hulless barley genotypes grown under one organic and three conventional management systems with increasing agrochemical input during 2011-2012. α-Tocopherol in grain and oil during both years ranged between 1.49-14.51 mg kg-1 and 9.24-88.32 mg 100 g-1 , respectively, with particularly low values in comparatively cooler and wetter year 2012. Total polyphenol content in grain and oil ranged between 81.66-140.13 and 0.19-8.52 mg gallic acid equivalents (GAE) 100 g-1 , respectively. We identified 13 phenolic compounds with the highest concentration for ferulic acid, followed by p-coumaric and syringic acids. No clear significant effect of crop management systems on the content of antioxidants was found. Conditions of the growing year had the greatest effect on the content of α-tocopherol, total polyphenol content and most phenolic compounds. α-Tocopherol content in barley grain and oil was generally higher under conventional management with higher input level; higher mean content was found for some hulless genotypes, although there was no significant difference between hulless and covered types. Higher total polyphenol content in grain was generally found under organic and lower input conventional management systems. Total polyphenol content was higher for covered barley genotypes in comparison to hulless genotypes. Higher total polyphenol content concentration in oil was found under medium intensive conventional management with covered genotypes being superior in 2011. The content of most phenolic compounds tended to increase with decrease of agrochemical input level and higher content was in covered than in hulless genotypes with some exceptions.

C-Alkyl (including C-arylmethyl) derivatives of Meldrum's acids are attractive building blocks in organic synthesis, mainly due to the unusually high acidity of the resulting compounds. Three examples, namely 5-[4-(diethylamino)benzyl]-2,2-dimethyl-1,3-dioxane-4,6-dione, C17H23NO4, (I), 2,2-dimethyl-5-(2,4,6-trimethoxybenzyl)-1,3-dioxane-4,6-dione, C16H20O7, (II), and 5-(4-hydroxy-3,5-dimethoxybenzyl)-2,2-dimethyl-1,3-dioxane-4,6-dione, C15H18O7, (III), have been synthesized, characterized by NMR and IR spectroscopy, and studied by single-crystal X-ray structure analysis. The nature of the different substituents resulted in remarkable differences in both the molecular conformations and the crystal packing arrangements. The presence of a substituent with a basic centre in compound (I) leads to the formation of an inner salt accompanied by drastic changes in the conformation of the 1,3-dioxane-4,6-dione fragment. By virtue of strong N-H···O hydrogen bonds, the residues are assembled into infinite chains with the graph-set descriptor C(10). Compound (II) contains methoxy groups in both the ortho- and para-positions of the arylmethyl fragment. Because of the absence of classical hydrogen-bond donors in this structure, the crystal packing is controlled by van der Waals forces and weak C-H···O interactions. Compound (III) contains methoxy groups in both meta-positions and a hydroxy group in the para-position. Supramolecular tetrameric synthons which comprise hydrogen-bonded dimers associated into tetramers through π-π interactions of overlapping benzene rings were observed.