stilbenes and benzaldehyde

The first total synthesis of (+)-schweinfurthin B, a potent and differentially active cytotoxic agent, has been accomplished. Completion of the synthesis required just 16 steps in the longest linear sequence from commercially available vanillin. Key synthetic transformations included a Shi epoxidation and an efficient cascade cyclization initiated by treatment of the resulting epoxide with BF(3).OEt(2). Furthermore, use of a methyl ether as a stable protecting group for benzylic alcohols dramatically increased the efficiency of the overall sequence. The benzylic ether can be removed from this electron-rich aromatic system through oxidation with DDQ that provided the desired aldehyde intermediate in quantitative yield and shortened the synthetic sequence. Introduction of the A-ring diol in the required cis stereochemistry then became viable through a short sequence highlighted by an aldol condensation with benzaldehyde to introduce an olefin as a latent carbonyl group at the C-3 position. This synthesis established for the first time the absolute stereochemistry of the natural product, and provides access to material on a scale that will advance biological studies. The total synthesis of the closely related compound (+)-schweinfurthin E also is reported.

Topics: Alkenes; Antineoplastic Agents; Benzaldehydes; Benzene Derivatives; Benzoquinones; Boranes; Cyclization; Epoxy Compounds; Ethers; Models, Chemical; Oxidation-Reduction; Stereoisomerism; Stilbenes

We describe the use of an on-line Raman analyzer to quantitatively track the levels of trans-stilbene, benzaldehyde, and alpha-methoxybenzyl hydroperoxide in a continuous flow ozonolysis reactor. Quantitative analysis is carried out using spectral stripping in order to overcome baseline artifacts inherent in simple peak area determinations and to incorporate prior knowledge into the analytical model. The performance of spectral stripping is compared to partial least squares (PLS) analysis. The effect of two process variables, feed flow rate and ozone concentration, are also explored. Finally, the benefit of utilizing an on-line technique is illustrated by demonstrating the bias introduced by sampling for off-line analysis.

Topics: Alkenes; Benzaldehydes; Ozone; Spectrum Analysis, Raman; Stilbenes

Synthetic analogues of the iron-bleomycins, namely [Fe(PMA)]2+ and [Fe(PMA)]+, have been studied as oxotransfer agents. Oxygen transfer has been observed using iodosobenzene (PhIO), hydrogen peroxide, and dioxygen as oxygen sources. The primary substrates were cis- and trans-stilbene. The products were determined to be cis- and trans-stilbene oxide, benzaldehyde, and deoxybenzoin. These products were recovered in ratios similar to those reported for the iron-bleomycins, albeit in lower yields. Iron complexes of simpler analogues are inactive as oxotransfer agents. This study provides further support that PMAH is an accurate model of the metal binding region of bleomycin.

Topics: Benzaldehydes; Benzoin; Binding Sites; Bleomycin; Chromatography, High Pressure Liquid; Electron Spin Resonance Spectroscopy; Ferric Compounds; Iron; Molecular Structure; Oxidation-Reduction; Oxygen; Stilbenes