New oxetane-type taxanes from Taxus wallichiana Zucc.

Abstract

The needles of Taxus wallichiana Zucc. gave the novel oxetane-type taxane diterpenoids 2 and 5, whose structures have been established on the basis of spectroscopic data and chemical reactions. The acidcatalysed rearrangement of 1 0-deacetyl baccatin I I I has been investigated.As part of a study on renewable sources of taxol and related compounds, we reported the isolation of 14-f3-hydroxy-10deacetylbaccatin I11 1 from the needles of the Himalayan yew (Tuxus wullichiunu Zucc.).' Compound 1 can be used as a synthetic precursor of hydroxylated derivatives of taxol,' and this prompted us to investigate further this plant for the presence of additional compounds potentially useful for the synthesis of antitumour taxoids. In the course of these studies, two new taxanes of the oxetane-type (2 and 5) were obtained from fractions less polar than those containing 1. R' R2 R3 R41 BnzH OHOH 2 H H OHOBnz 3 BnzOHH OH (Bnz = benzoyl)

Anionic and Photochemical Behaviour of the Medium‐Sized Terpenoid Ketone 8‐Dehydro‐12‐O‐methyl‐deacylhallerin

“…[3,4] Much less is known about the anionic rearrangements of this type of compounds, [5] as well as about their photochemical behaviour. [6,7] To complement previous studies on the cationic rearrangements of medium-sized terpenoids, [8,[9][10][11] we have now investigated the behaviour of the enone 2 toward bases and light, supporting the experimental results with X-ray crystal structure data and theoretical molecular dynamics (MD) and quantum chemical calculations.…”

“…The presence of a ketone carbonyl group was viewed as critical for induction of anionic and photochemical behaviour. Ketone 2 emerged as a suitable substrate because of its availability in multigram amounts by modification of the natural product hallerin (1) [8,10] and the presence of the reactive 1,4-diene system.…”

New 14-Hydroxy-taxane and 2α,20-Epoxy-11(15→1)abeotaxane from the Needles ofTaxus canadensis

“…The chemical shift of C-1 at C 59.4, an unusual downfield chemical shift for an unoxygenated quaternary carbon, together with the absence of long-range correlation between C-11 and C-16/C-17, 7) strongly indicated that taxane 2 possessed an 11(15!1) rearranged skeleton, i.e., a brevifoliol analogue. 9) This conclusion was further confirmed by the observation of long-range correlation from H-10 to C-1 in the HMBC data. The assignment of functional groups was started with the signal at 2.27 (1H, d, J ¼ 7:4 Hz), typical of an H-3 ring junction proton.…”

Chemistry and Structure—Activity Relationships of Taxoids with Modified Skeletons

“…As with other terpenoids, Wagner-Meerwein rearrangement occurs to the Α-ring of taxoids bearing a tertiary hydroxyl group at C-l (33)(34)(35). Kingston and his collaborators (33) found that treatment of the 7, 2'-(9-diprotected paclitaxel derivative with mesyl chloride and subsequent deprotection led to the Α-ring contracted derivative 18 which possesses an antitubulin activity similar to that of paclitaxel (33).…”

“…On the other hand, compound 20 and 21 were obtained after treatment of 10-deacetylbaccatin ΙΠ with /rara-toluene sulfonic acid in methanol (35).…”