Cyclohexadiene-trans-diols as versatile starting material in natural product synthesis: short and efficient synthesis of iso-crotepoxide and ent-senepoxide

A new synthesis of ent-senepoxide and iso-crotepoxide starting from microbially produced(+)-trans-2,3-dihydroxy-2,3-dihydrobenzoic acid via regio- and stereoselective epoxidation is described.     

Zur Ausbreitung der Entladung in selbstlöschenden Zählrohren. VI

The dependence on time and space of the discharge process in a selfquenching GM counter was measured with an oscilloscope. For this reason the cathode of the counter tube was composed of several isolated rings. The analysis of the pulse shapes measured with and without an electrical filter shows that, in most cases, the discharge of a self quenching counter tube spreads quasi-continuously along the wire by photoelectric effect in the counter gas.     

Synthesis of site-specifically labeled arachidonic acids as mechanistic probes for prostaglandin H synthase

[structure: see text] Prostaglandin H synthase catalyzes the first committed step in the biosynthesis of prostaglandins and thromboxane. Herein we report the synthesis of four site-specifically labeled arachidonic acids for investigation of the radical intermediate formed during this enzymatic reaction. Two compounds were prepared using a common C9-C11 fragment, while another target was synthesized using a previously reported advanced intermediate. An alkyne coupling followed by hydrogenation and Wittig reaction was used to prepare the final labeled substrate.     

The structure of cleomeolide, an unusual bicyclic diterpene from cleome viscosa L. (capparaceae)

A bicyclic diterpene cleomeolide (1) C₂₀H₃₀O₃ has been isolated from Cleome viscosa L. (Capparaceae), and its stereostructure established by chemical, spectral and X-ray crystallographic means. Crystals of 1 belong to space group P2₁ with A = 10.329(2)Å, B = 12.468(3)Å, C= 7.356(2)Å,β = 109.98°, and Z = 2. The structure was solved by a multiple solution procedure and refined by full matrix least-squares to give R = 0.041 and wR = 0.051. Oxidation of 1 gave the ketone 4, which on treatment with methanolic KOH led to a facile transannular reaction to give the lactone 6     

Modeling of infrared soft-tissue photoablation process

Received: 2 September 1996/Revised version: 17 February 1997