The pregnane derivatives of the seeds from Dregea abyssinica (Hochst.) K. Schum. (Asclepiadacea). I. Isolation

The seeds of Dregea abyssinica (HOCHST .) K. Schum. are very rich in glycosides. These consist of a complicated mixture of ester glycosides, cardenolides are absent. All these glycosides are derived from only the two known pregnane derivatives drevogenin P and Drevogenin D. In the glycosides the latter are esterified with different acids (acetic, isovaleric, α-hydroxyisovaleric and tiglic acid) and glycosidically linked to different 2-deoxy-sugars which in part carry 3-O-methyl-6-deoxy-D-allose and terminal D-glucose. After mild acidic hydrolysis 5 crystalline sugars and 6 crystalline aglycones could be isolated. The sugars were identified as D-cymarose, asclepobiose, pachybiose, drebyssobiose and «sugar T» (formerly found in Dregea volubilis). The following aglycones were obtained: drevogenin A, drevogenin B, and four new compounds called drebyssogenin F, G, J and K. The latter was a mixture of two components (K1 and K2). From the original mixture four genuine glycosides could be isolated (the drebyssosides 1, 2, 3 and 4). Of these the drebyssosides 1 and 3 were obtained crystalline, drebyssoside 2 in amorphous but pure form and drebyssoside 4 as a mixture of mainly two closely related components. The probable structures of the new substances (drebyssobiose, sugar T, the four drebyssogenins and the four drebyssosides) are reported in the following publication.     

The pregnane derivatives of the seeds from Dregea abyssinica (Hochst.) K. Schum. (Asclepiadacea). II. Structure determination

The total or partial structure determinations of some new components from Dregea abyssinica are reported. The four drebyssogenins (F, G, J and H) are esters of the drevogenins P ( 7 ) and D( 9 ) and have the following structures: Drebyssogenin F ( 5 ) = 11-O-acetyl-12-O-(α-hydroxyisovaleryl)-drevogenin P, drebyssogenin G ( 14 ) = 11-O-acetyl-12-O-isovaleryl-drevogenin D, drebyssogenin J ( 15 ) = 11, 12-di-O-acetyl-drevogenin D. Drebyssogenin K is a mixture of K1 ( 16 ) and K2 ( 17 ), the mono-O-tiglyl and mono-O-isovaleryl derivatives of drevogenin D respectively, with as yet undetermined position of the acyl residues. The drebyssosides 1, 2 and 3 are glycosides of trisaccharides. Drebyssoside 1 ( 2 ) is pachybiosyl-cymarosyl-drevogenin A, drebyssoside 2 ( 3 ) asclepobiosyl-cymarosyl-drevogenin A and drebyssoside 3 ( 6 ) pachybiosyl-cymarosyl-drebyssogenin F. Drebyssoside 4 is a mixture of at least two components and contains the same aglycones and the same sugar units as the drebyssosides 1 and 3, but is different from them. The full structure of the two sugars (drebyssobiose ( 25 ) and sugar T ( 24 )) has not been determined; it is only shown that both are disaccharides which contain 3-O-methyl-6-deoxy-allose linked to a 2-deoxyhexose.     

A metallo base-pair incorporating a terpyridyl-like motif: bipyridyl-pyrimidinone.Ag(I).4-pyridine

The design and characterization of a geometrically unique, metallo base-pair motif is reported.     

First data from a commercial local electrode atom probe (LEAP).

The first dedicated local electrode atom probes (LEAP [a trademark of Imago Scientific Instruments Corporation]) have been built and tested as commercial prototypes. Several key performance parameters have been markedly improved relative to conventional three-dimensional atom probe (3DAP) designs. The Imago LEAP can operate at a sustained data collection rate of 1 million atoms/minute. This is some 600 times faster than the next fastest atom probe and large images can be collected in less than 1 h that otherwise would take many days. The field of view of the Imago LEAP is about 40 times larger than conventional 3DAPs. This makes it possible to analyze regions that are about 100 nm diameter by 100 nm deep containing on the order of 50 to 100 million atoms with this instrument. Several example applications that illustrate the advantages of the LEAP for materials analysis are presented.