Steroide und Sexualhormone. 248. Mitteilung. Die Partialsynthese von 5α-Dihydrohirundigenin und von 5α-dihydroanhydrohirundigenin

A partial synthesis of dihydroanhydrohirundigenin ( 4 ), a hydrogenation product of naturally occurring anhydrohirundigenin ( 2 ) is described. Furthermore 4 is transformed into the formal dihydroderivative 14 of hirundigenin ( 1 ).     

«Push-Pull»-Acetylene als Hilfsmittel zur Synthese von Amiden

Amide Synthesis by Means of ‘Push-Pull’-Acetylenes ‘Push-Pull’-acetylenes react easily with carbon acids, Addition of amines to the crude reaction mixture gives amides in an excellent yield by a simple one-pot procedure. Because of the high selectivity of the acetylenes 1 towards carboxylic functions and of the high selectivity of the enol esters 4 towards amine functions, ‘push-pull’-acetylenes could be excellent reagents for peptide synthesis.     

Accurate measurement of one-bond H-X heteronuclear dipolar couplings in MAS solid-state NMR

The accurate experimental determination of dipolar-coupling constants for one-bond heteronuclear dipolar couplings in solids is a key for the quantification of the amplitudes of motional processes. Averaging of the dipolar coupling reports on motions on time scales up to the inverse of the coupling constant, in our case tens of microseconds. Combining dipolar-coupling derived order parameters that characterize the amplitudes of the motion with relaxation data leads to a more precise characterization of the dynamical parameters and helps to disentangle the amplitudes and the time scales of the motional processes, which impact relaxation rates in a highly correlated way. Here. we describe and characterize an improved experimental protocol--based on REDOR--to measure these couplings in perdeuterated proteins with a reduced sensitivity to experimental missettings. Because such effects are presently the dominant source of systematic errors in experimental dipolar-coupling measurements, these compensated experiments should help to significantly improve the precision of such data. A detailed comparison with other commonly used pulse sequences (T-MREV, phase-inverted CP, R18(2)(5), and R18(1)(7)) is provided.     

Bubble clustering and trapping in large vortices. Part 1: Triggered bubbly jets investigated by phase-averaging

The characteristics of large coherent structures in turbulent, periodically-excited, as well as naturally-developing bubbly jets are investigated, and interactions between bubbles and large-scale vortices are studied quantitatively.     

Ring-opened analogues of Ambrox®: Synthesis and Structure-Odour relationships

Eight bicyclic ether derivatives 11 – 18 , related to the tricyclic odorant Ambrox^® ( 1 ) and its analogues 2 – 6 by formal heteroring-opening, have been prepared; their odoriferous activity/in activity is correlated with the steric accessibility of the ether O-atom, calculated by computer-aided molecular modeling.