No abstract

Organoselenium resins 1–4 were prepared from polystyrene via lithiation and quenching with MeSeSeMe, and shown to react with a variety of substrates, aiding in useful functionalizations

No abstract

No abstract

A B S T R A C T Prostacyclin (PGI2) is the most potent, naturally occurring inhibitor of platelet aggregation known. To determine whether PGI2 is bound by platelets, high specific activity [9-3H]PGI2 was synthesized by iodination and subsequent base treatment of the labeled precursor [9-3H]prostaglandin (PG)F, methyl ester. Binding experiments were performed at room temperature with normal citrated human platelet-rich plasma that contained [14C]sucrose or ['4C]PGF,l< as an internal marker for the extracellular space. Binding of [3H]PGI2 plateaued within 2 min and this bond radioactivity could be displaced rapidly by excess nonradioactive PGI2. Scatchard analysis of concentration-dependent binding yielded a hyperbolic plot which appeared to be caused by the existence of two classes of binding sites. The higher affinity class has a dissociation constant of 12.1±2.7 nM and a capacity of 93 (±21)sites per platelet. The lower affinity class had a dissociation constant of 0.909±t.236 ,uM and a capacity of 2,700+700 sites per platelet. The relative ability of PGI2, PGE1, PGE2, and 6-keto-PGFi,a to displace[3H]PGI2 initially bound to the higher affinity class of sites were 100:5:<0.3: <0.3. These relative abilities parallel the relative potencies of these compounds as inhibitors ofADP-induced platelet aggregation in vitro.However PGD2, which is more potent than PGE, as an inhibitor of aggregation, did not displace bound [3H]PGI2. The higher affinity binding site for PGI2 appears to be the specific receptor through which PGI2 exerts its effect on platelets.

Abstract:A new photolabile linker enabling nucleophilic cleavage of a carboxyl functionality upon irradiation with UV light (>290 nm) was developed. When the photocleavage is carried out in the presence of primary or secondary amines, amides are obtained in high yields and purities, while the intramolecular version of this reaction leads to heterocycles via a cyclorelease mechanism.

With its imposing structure, brevetoxin B (1), produced by Gymnodinium breve Davis, stood as a formidable challenge to synthetic chemists since its discovery and structural elucidation in 1981.1 Brevetoxin's beautifully arranged molecular assembly includes 11 transfused rings, each containing an oxygen atomf with each fusion consisting of a C-C bond separating two adjacent ring oxygens and with all adjacent substituents flanking the oxygens placed syn to each other except on ring K. Its unprecedented architecture, its association with the "red tide" catastrophes,2 and its potent neurotoxicity and interference with the function of sodium channels attracted serious attention from chemists3 and biologists4 alike. We now wish to announce, in this and the following communication,5 the total synthesis of brevetoxin B (1) in its naturally occurring form. Figure 1 outlines the strategic bond disconnections and retrosynthetic analysis of 1. The adopted strategy benefited from convergency (oxocene disconnections) and synthetic technolo gies developed in these laboratories specifically for constructing oxocene6 and tetrahydropyran7 systems.

No abstract