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71.
Halichonic acid,a new rearranged bisabolene-type sesquiterpene from a marine sponge Halichondria sp.
Kenta Raiju Yuki Hitora Hikaru Kato Yuji Ise Esther D. Angkouw Remy E.P. Mangindaan Sachiko Tsukamoto 《Tetrahedron letters》2019,60(15):1079-1081
A new compound, halichonic acid (1), was isolated from a marine sponge Halichondria sp., together with (6R,7S)-7-amino-7,8-dihydro-α-bisabolene (2). The structure of 1 was elucidated by spectroscopic analysis and ECD spectrum calculation to be a rearranged bisabolene-type sesquiterpene having a 3-azabicyclo[3.3.1]nonene moiety. Compound 2 was cytotoxic against HeLa cells with an IC50 value of 50?μM, whereas 1 did not show cytotoxicity even at 50?μM. It is possible that 1 is biosynthesized from farnesyl pyrophosphate and glycine, with rearrangement. 相似文献
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The normal dissolution rates, the slopes and the average velocities of dissolution steps of etch pits on the (111) face of a K-alum crystal, originating from dislocations with Burgers vector 110, were measured in relation to the surface undersaturations. From the mutual relations, it was shown that the dissolution was controlled by both diffusion and surface kinetic processes, although the contribution of the latter process was smaller than in the case of growth. It was also demonstrated that the normal dissolution rate was always larger than the growth rate. This is attributed to the fact that the slopes of growth hillocks are invariably smaller than those of etch pits. 相似文献
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Stefan Eißler Dr. Tobias Bogner Dipl.‐Biochem. Markus Nahrwold Dr. Norbert Sewald Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(42):11273-11287
Cryptophycins are a family of highly cytotoxic, cyclic depsipeptides. They display antitumour activity that is largely maintained for multi‐drug‐resistant tumour cells. Cryptophycins are composed of four building blocks (units A–D) that correspond to the respective amino and hydroxy acids. A new synthetic route to unit A allows the selective generation of all four stereogenic centres in a short, efficient and reliable synthesis and contributes to an easier and faster synthesis of cryptophycins. The first two stereogenic centres are introduced by a catalytic asymmetric dihydroxylation, whereas the remaining two stereogenic centres are introduced with substrate control of diastereoselectivity. The stereogenic diol function also serves as the epoxide precursor. The approach was used to synthesise the native unit A building block as well as three para‐alkoxymethyl analogues from which cryptophycin‐52 and three analogous cryptophycins were prepared. Macrocyclisation of the seco‐depsipeptides was based on ring‐closing metathesis. 相似文献
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The role of the In/Si(111)-(4 x 1)-In surface as an atomic-scale geometrical template for the growth of Ag thin films is clarified by scanning tunneling microscopy and low energy electron diffraction. Low-temperature grown Ag films are found to have stripe structures with a transverse periodicity equal to that of indium chains of the In/Si(111)-(4 x 1)-In. The stripes exhibit a structural transformation at the thickness of 6 monolayers (ML); this relaxation allows the stripes to persist up to a thickness as large as 30 ML (approximately = 7 nm) while maintaining their mean periodicity. We attribute this stability to a coincidental matching of the periodicity and the corrugation amplitude between the Ag film and the substrate, which is realized by periodic insertion of stacking faults into a Ag fcc crystal. 相似文献
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