Tasumatrols P – T,Five New Taxoids from Taxus sumatrana

The phytochemical investigation of the more polar fractions from the leaves and twigs of Taxus sumatrana (Taxaceae) afforded five new taxane diterpene esters, tasumatrols P–T ( 1 – 5 ) possessing an 11(15→1),11(10→9)‐diabeotaxane skeleton. Compounds 1, 4 , and 5 contain an α‐hydroxy group at C(14), while 3 has no OH group at either C(13) or C(14). Compound 2 is a natural 4,5‐acetonide derivative, while 4 has an unusual spiro‐connected 2‐hydroxy‐2‐phenyl‐1,3‐dioxolane ring. Ten known taxoids, were also isolated in the course of the chromatographic fractionation. Five additional new O‐acetyl derivatives 3a, 4a, 4b, 5a , and 5b were prepared from the taxanes 3 – 5 . The structures of all new compounds were established on the basis of their spectroscopic analyses. Compound 1 showed mild cytotoxic activity against human Hela and Daoy tumor cells.     

A remark on convex functions andp-harmonic maps

We prove that the constant maps are the onlyp-harmonic maps for anyp 2 from an arbitrary compact Riemannian manifold into a complete Riemannian manifold which admits a strictly convex function.     

Pulsed-laser photolysis of chromium and molybdenum hexacarbonyls at 308 nm: Simultaneous monitoring of optical and acoustic emissions

An acoustic technique developed earlier was applied to measure the molar number of fragments produced in the XeCl-laser-induced gas-phase photolysis of Cr(CO)₆ and Mo(CO)₆. The bluish-green Cr and Mo emissions were also monitored and correlated with the acoustic signal. For laser fluence ranging up to about 25 mJ/cm² (38 mJ/cm²), the Cr (Mo) optical signal varied with laser fluence asy =dx ³, in agreement with the model that highly excited metal atoms were produced by direct three-photon processes. The acoustic signal varied with fluence asy = ax + bx ², consistent with the model that most fragments were formed via sequential and direct two-photon processes. Quite expectedly, all coefficientsa,b andd vary linearly with carbonyl partial pressure. Both optical and acoustic signals showed onset of saturation at 25 mJ/cm² (38 mJ/cm²) for the case of chromium (molybdenum) hexacarbonyl, suggesting that all photolysis channels were equally affected by the depletion of parent molecules. By assuming a common depletion mechanism, upper limits on the branching ratios of the various photolysis channels were estimated.