S., A new solvent system for efficient synthesis of 1,2,3-triazoles.
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K., New methods for the synthesis of heterocyclic compounds.
These unique materials are produced by plants throughout the world as phytoalexins, serving as a first line of chemical defense against stresses such as fungal infections. That role may derive from the fact that these molecules, including 8–20 (), can be formed readily from resveratrol (4) through its self-merger anywhere between two, and upwards of ten, times through numerous distinct C-C and C-O bond constructions. Indeed, to put that bond-forming diversity into perspective, most other similarly-produced oligomer families have just one or two specific combination modes. Although the biogenesis of this family remains an open question, a number of studies,, point to a reasonable hypothesis based on two main phases of construction, stages that could be viewed as similar to the cyclase and oxidase paradigm of terpene biosynthesis., In the first, radical and/or cation-based reaction cascades convert resveratrol (4) into multiple dimeric frameworks, including 8–15. These cores may result either through direct dimerization of 4 or rearrangement reactions of a given dimer (especially ε-viniferin, 8) into additional frameworks under appropriate conditions to create an initial base of architectural and stereochemical diversity., Whether enzymes are involved in these processes is unknown, though the participation of some chiral entity at some stage seems reasonable given that many of these materials are isolated in an optically active form.
O., Synthesis of new heterocyclic fatty compounds.
From these staging areas, further oligomerization can occur in a second synthesis stage, with one seemingly prevalent mode being the addition of new resveratrol units to generate dihydrofuran rings. As indicated by the representative structures shown for compounds 16–20- derived from the pallidol (12) and ampelopsin F (14) cores, these new ring systems are added with inconsistent regio- and stereospecificity. Though it is unknown the degree to which a given plant species can dictate the synthetic distribution of these variants (and again whether enzymes are even involved in such processes), from a global perspective the possibility of concurrently garnering such diversity is likely advantageous since it affords a broader range of architectures and potential biochemical properties. Indeed, initial screens have shown that activity is correlated with both size and stereochemistry. For example, while resveratrol (4) possesses broad spectrum activity in murine models (and is implicated in the “French paradox” in humans),, the addition of increasing numbers of resveratrol units affords compounds with greater specificity and potency.,, Similarly, while ampelopsin H (17) and nepalensinol B (20) have the same cores, their stereochemical differences lead to different mechanisms of anti-cancer activity.,
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