The results from a third structure determination by powder diffractometry ͑SDPD͒ round robin are discussed. From the 175 potential participants having downloaded the powder data, nine sent a total of 12 solutions ͑8 and 4 for samples 1 and 2, respectively, a tetrahydrated calcium tartrate and a lanthanum tungstate͒. Participants used seven different computer programs for structure solution ͑ESPOIR, EXPO, FOX, PSSP, SHELXS, SUPERFLIP, and TOPAS͒, applying Patterson, direct methods, direct space methods, and charge flipping approach. It is concluded that solving a structure from powder data remains a challenge, at least one order of magnitude more difficult than solving a problem with similar complexity from single-crystal data. Nevertheless, a few more steps in the a͒

The development of effective protecting group chemistry is an important driving force behind the progress in the synthesis of complex oligosaccharides. Automated solid-phase synthesis is an attractive technique for the rapid assembly of oligosaccharides, built up of repetitive elements. The fact that (harsh) reagents are used in excess in multiple reaction cycles makes this technique extra demanding on the protecting groups used. Here, the synthesis of a set of oligorhamnan fragments is reported using the cyanopivaloyl (PivCN) ester to ensure effective neighboring group participation during the glycosylation events. The PivCN group combines the favorable characteristics of the parent pivaloyl (Piv) ester, stability, minimal migratory aptitude, minimal orthoester formation, while it can be cleaved under mild conditions. We show that the remote CN group in the PivCN renders the PivCN carbonyl more electropositive and thus susceptible to nucleophilic cleavage. This feature is built upon in the automated solid-phase assembly of the oligorhamnan fragments. Where the use of a Piv-protected building block failed because of incomplete cleavage, PivCN-protected synthons performed well and allowed the generation of oligorhamnans, up to 16 monosaccharides in length.

This article reports on the synthesis, thermal behavior, and morphology of phase change materials based on diesters from 1,4butanediol with palmitic (BD16), stearic (BD18), or behenic (BD22) acid. The crystalline contents and melting enthalpies of all substances exceed 90% and 180 J/g, respectively. The molecules display monotropic polymorphism. The metastable β′ form is built from outstretched molecules, whereas the denser, stable β form is composed of molecules with a kinked conformation. BD18 and BD22 crystallize into the β′ form during cooling. Only BD18 transforms into the β form during subsequent heating via a solid−solid transition. The resistance of BD22 to convert into the β form is believed to originate from the lack of mobility associated with longer aliphatic chains. In contrast, the polymorphic conversion is thought to be very efficient and to take place during cooling for the shorter BD16 molecules. The hypothesis is put forward that the original BD16 β′ nuclei are rapidly overgrown by the β phase by which crystal growth is postponed to larger supercooling where the β phase can grow from the melt. Consequently, BD16 only occurs in the β form. The melt crystallization of BD18 and BD22 into the β′ form hardly requires any supercooling.

Iminosugars are an important class of natural products and have been subject to extensive studies in organic synthesis, bioorganic chemistry and medicinal chemistry, yet only a limited number of these studies are on glycosylated iminosugars. Here, a general route of synthesis is presented towards glycosylated 1‐deoxynojirimycin derivatives based on the oxidation–reductive amination protocol that in the past has also been shown to be a versatile route towards 1‐deoxynojirimycin. The strategy can be applied on commercial disaccharides, as shown in four examples, as well as on disaccharides that are not commercially available and are synthesized for this purpose, as shown by a fifth example.

The synthesis of bacillosamines carrying different functionalities at their C-2 and C-4 amine groups is described for the first time.