Crystallographic structure determination of the diterpenoid baccatin-V, a naturally occurring oxetan with a taxane skeleton

Abstract

Baccatin-V, C3,H3,01,, a new diterpenoid from Taxus baccata L. has been shown by X-ray analysis to contain an oxetan ring and to be 5@,20-epoxy-l@,2a,4a,-7a, log, 13~-hexahydroxytax-1 1-en-9-one 4a, 1 OP-diacetate 2cc-benzoate (I).

Clean Nanotube Unzipping by Abrupt Thermal Expansion of Molecular Nitrogen: Graphene Nanoribbons with Atomically Smooth Edges

“…From SEM, TEM, and AFM images (see Figure 1, Figure 2, Figure 3, Figures SI-1 and SI-2), we did not find as many single-, bi-, and few-layer structures as in GO. 32 In addition, our XPS spectra show that acid treatment creates oxidation on our MWNTs; however, the intensity and width of the oxidation peaks show that the oxygen functionality content is much lower when compared to GO. 32À37 Our X-ray diffraction patterns (see Figure SI-3a) reveal large spacings similar to those observed for GO; nevertheless, we believe that in our case it is due to intercalation of acid and not graphene oxide production, as previously discussed.…”

“…The high resistivity in the CN x -A and CN x -F samples (Figure SI-8a) could be explained by the presence of bare edges and functional groups within the carbon nanotubes caused by the acid treatment and the thermal shock; however, these resistivity values are much lower values than those reported for graphene oxide. 32,40 Surprisingly, the heat-treated ribbon material (CN x -FHT), reduced the oxygen functionality content (see Figure 4g and Table SI-2), revealing a clear decrease in electrical resistivity, 5 times lower than that of the pristine CN x -MWNT sample. However, the annealed ribbons consist of conglomerated ribbons and planes that had experienced some morphological changes.…”

Biological Activity and Chemistry of Taxoids from the Japanese Yew, Taxus cuspidata

“…These taxoids possess various skeletons containing 5/7/6, 6/10/6, 6/5/5/6, 6/8/6, or 6/12-membered ring systems. It is noted that the non-paclitaxel-type taxoids, taxuspine D (4), taxezopidines K (35) and L (36), and taxagifine (49), exhibit potent inhibitory activity against Ca 2+ -induced depolymerization of microtubules, while taxuspine D (4) induced spindles with strong birefringence in the same manner as paclitaxel (53). Some natural taxoids (2, 3, 9, 23, 32, 33, 41, 42, 44, 45, 75, 96, 97, and 98) and synthetic taxoids (123-134) increase VCR accumulation in MDR cells.…”

“…The structures of taxuspines F (6) and G (7) and taxezopidines C (28), D (29), and E (30) have a cyclohexenone (ring A) and a C-4(20)exomethylene unit. Taxuspine D (4) was the first example of a taxoid involving an enol acetate moiety in ring A, while similar taxoids, taxuspine P (15), taxezopidine K (35), and compound 85, were also isolated from T. cuspidata. The conformation of ring B in these compounds is different from those of other taxoids having a 6/8/6-membered ring system, judging from comparison of the 1 H-1 H coupling constants (J 9,10 ) 4.4-4.8 Hz) of 4, 15, and 35 with those (J 9,10 ) ca.…”

“…The CaCl 2 -induced depolymerization of microtubules (shown as control) is completely inhibited by 10 µM paclitaxel (53). Among the tested taxoids, taxuspine D (4), taxezopidine K (35), taxezopidine L (36), and taxagifine (49) reduced the depolymerization process in a remarkable fashion, suggesting that these compounds have paclitaxellike activity to microtubule systems. The potencies of 4, 35, 36, and 49 in inhibiting the depolymerization process corresponded to half to one-third of that of paclitaxel (53).…”