No abstract

The photodeconjugation of the alpha-(4-trimethylsilyl-3-butynyl)-substituted senecio acid esters 7 was studied. Chiral alcohols ROH (9) were employed as auxiliaries to control the facial diastereoselectivity of the protonation step. The conversion of the four sugar alcohols diacetone-D-glucofuranose, diacetone-D-allofuranose, diacetone-D-gulofuranose, and diacetone-D-fructopyranose (9a-d) to the esters 7 was achieved in four steps employing 4-iodo-1-trimethylsilylbut-1-yne (3) as the alkylating agent (27-45% yield overall). Their photodeconjugation gave the corresponding beta,gamma-unsaturated (R)-esters 14a-d with moderate to excellent diastereomeric excess. The best results were achieved with diacetone-D-glucofuranose and diacetone-D-fructopyranose as the auxiliary (>95% de). To achieve the synthesis of the target compound 1 which has the (S)-configuration, the deconjugation was conducted with the diacetone-L-fructopyranose (ent-9d) derived ester ent-7d. L-Fructose (20) was prepared from L-sorbose (15) in a modified procedure that allowed for the isolation of intermediates. The 2-fold inversion of configuration worked nicely, and the fructofuranose 19 was obtained in 19% yield from L-sorbose. The conversion of L-fructose to the ester ent-7d was conducted in full analogy to the synthesis of its enantiomer 7d. Deconjugation of ester ent-7d yielded the product 2d (70% yield), which was reduced to the alcohol 1 (85% yield).

General findings concerning storage behaviour in freeze drying are likely to be applicable in MWFD with only slight adjustments.

The three carbohydrates sorbitol, trehalose, and maltodextrin, differing in molecular weight, were investigated as excipients to enhance survival of the probiotic strain Lactobacillus paracasei ssp. paracasei F19 during a microwave‐assisted freeze‐drying process. This technique was further compared to conventional freeze‐drying, where thermal energy is supplied by heat conduction instead of radiant energy. Survival rates revealed similar values for both techniques after drying without protectants (~10%). While addition of maltodextrin and trehalose led to a two‐ up to threefold increase in survival for both dryings, sorbitol containing samples showed the greatest difference between the two techniques: 65% after freeze‐drying versus 12% after microwave freeze‐drying. Though protection mechanisms were generally found to be equal to conventional lyophilization, microwaves are likely to induce vibrations in the hydrophilic sugars. Thus, not all protectants which are applicable in freeze‐drying, can be applied in microwave freeze‐drying to enhance bacterial viability. Practical applications A new drying process for the efficient preservation of bacterial cultures, such as lactic acid bacteria, was investigated. Microwave freeze‐drying is a much faster and less costly process than conventional freeze‐drying leading to equal product qualities and reducing the problem that drying often is the bottleneck in industrial biotechnological processes. However, no work on microwave freeze‐drying of bacterial cultures has been published so far. Knowledge on the impact of protectants on the survival of the cultures is a crucial aspect to make microwave freeze‐drying applicable in industrial processes. The selection of proper protectants is important to achieve high survival after drying and during storage.

The dibromofuran 6 was prepared in four steps from dibromofurfural 3 in 73% yield. It was regioselectively metalated by a bromine-magnesium exchange reaction and was added to aldehyde 7. Alcohol 8 was obtained by this key step in 75% yield. Further functionalization reactions led to the precursors 17-19 for an intramolecular Nozaki-Hiyama coupling. The ring-closing Nozaki-Hiyama protocol was successfully implemented in the synthesis of the macrocyclic propargylic alcohol 20.