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[reaction: see text] A strategy for synthesis of the hexahydroxanthene moiety of the natural products schweinfurthin A, B, and D is described. The relative stereochemistry in the key cationic cyclization step is established through the preference of the phenylselenide substituent for an equatorial orientation.

Salicortin, a natural product abundant in most members of the Salicaceae family, is a mechanism-based inactivator of Agrobacterium faecalis beta-glucosidase. Inactivation is delayed in the presence of competitive inhibitors, thereby demonstrating the requirement for an enzyme-bound salicortin before inactivation. Product studies suggest that inactivation proceeds via a quinone methide intermediate formed by the fragmentation of the aglycone of salicortin while it is bound to the enzyme. Tryptic digest and HPLC/MS studies confirm the role of quinone methide attack and also show that the enzyme undergoes multiple modifications. In addition, when the inactivation was run in the presence of a mutant inactive form of the enzyme, HPLC/MS analyses clearly showed no modification of the mutant enzyme, demonstrating that the quinone methide does not exist in free solution and suggesting that inactivation is active-site directed.

A new prenylated benzoic acid, arieianal [3,4-dihydroxy-5-(E,E, E-11'-formyl-3',7',15'-trimethylhexadeca-2',6',10', 14'-tetraenyl)benzoic acid, 1], has been isolated from the leaves of Piper arieianum and assigned this structure on the basis of its spectral data.

Key indicatorsSingle-crystal X-ray study T = 298 K Mean (C-C) = 0.003 Å R factor = 0.050 wR factor = 0.148 Data-to-parameter ratio = 12.2For details of how these key indicators were automatically derived from the article, seeThe molecular structure of (I), showing the atom-numbering scheme and displacement ellipsoids drawn at the 50% probability level.

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Plant material was collected between July and September 1995, mainly off of Groin road in the Chena Flood Plain located near North Pole, Alaska. Additional samples were collected along the Parks, Nenana, Richardson, and Steese Highways of interior Alaska. Voucher specimens (ALA ext #V119746, V119747) were deposited at the University of Alaska Museum. The samples were separated into root, seed, leaf, flower, and stem parts and immediately stored at -20 o C except for the flowers which were first freeze-dried.An exhaustive extraction of each Hedysarum sample was performed by three successive two-day extractions in acetone (10mL/g plant material). For the total extract, the combined extracts were concentrated and lyophilized. For the "alkaloid" samples, the combined extracts were concentrated and then partitioned between CHCl 3 and 1M HCl, and the organic layer extracted twice more with HCl. The aqueous layer was rendered basic with saturated NaHCO 3 and extracted with CHCl 3 . Is Hedysarum mackenziei (Wild Sweet Pea) Actually Toxic?Edward M. Treadwell and Thomas P. Clausen Research AbstractHedysarum mackenziei Richardson (wild sweet pea, bear root) is widely regarded as toxic and warnings about confusing it with its edible cousin Hedysarum alpinum Richardson (Eskimo potato) abound. To find the chemical basis for this claim, we performed an exhaustive comparison of the secondary chemistry between the two plants as well as a search for nitrogen containing metabolites (alkaloids) in both species. No chemical basis for toxicity could be found. These results were consistent with a subsequent cytotoxic assay performed on an extract of H. mackenziei. Finally, a critical examination of the literature could find no credible evidence that H. mackenziei is toxic in spite of these widespread rumors.

The linkage isomers [(OC) 5 W{κ 1 -PPh 2 CH 2 CH(PPh 2 )[P-(p-tol) 2 ]}] 3a, [(OC) 5 W{κ 1 -P(p-tol) 2 CH(PPh 2 )CH 2 PPh 2 }] 3b, and [(OC) 5 W{κ 1 -PPh 2 CH[P(p-tol) 2 ]CH 2 PPh 2 }] 3c isomerize at ambient temperatures to give a mixture of the three isomers in equilibrium.Rates of isomerization and equilibrium constants have been measured at temperatures from 10 to 55 °C, and from these, enthalpies and entropies have been determined. The isomerization reactions are initiated by a nucleophilic attack of a pendant phosphine on a bound carbonyl group followed by dissociation of a coordinated phosphine. These studies lead us to suggest that the k 2 term in the rate law for CO replacement by phosphines is based on a similar mechanism and offers a plausible clarification of the currently accepted understanding. The crystal structure of 3b, the most stable of the three isomers, has been determined.