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Radical Coupling Reactions in Lignin Synthesis: A …

Boerjan W, Ralph J and Baucher M (2003) Lignin biosynthesis. Annual Reviews in Plant Biology 54: 519–549.

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13/04/2012 · Radical Coupling Reactions in Lignin ..

Lignins, complex and irregular polymers present in the cell walls of vascular plants, are built from three basic monolignols. An understanding of their nature is evolving as a result of detailed structural investigations aided by improvements in analytical methodologies and the availability of mutant and transgenic plants. Oxidative phenolic coupling reactions, where monomers primarily couple endwise with the growing chain, generate the polymer. The combinatorial linkage synthesis, the random generation of new optical centres each time a monolignol couples via its sidechain, and the inclusion of monomers other than the monolignols, cascade to create polymers with enormous variation in primary structure. Lignification is a strategic process that has evolved to allow plants considerable flexibility in dealing with various environmental stresses. The malleability offers significant opportunities to engineer the structures of lignins beyond the limits explored to date.

Whetten R and Sederoff R (1995) Lignin Biosynthesis. Plant Cell 7: 1001–1013.

We compute reaction enthalpies for the initial self- and cross-coupling reactions of these monolignol radicals to form dimeric intermediates via six major linkages observed in natural lignin.

2010_Faravelli_ThermalDegradationOfLignin

For selected recent examples of intermolecular radical addition reactions in the total synthesis of terpenoids, see:

Further demonstrating the scope and value of organometallic chemistry are the novel examples of lactone and lactam syntheses based on organoiron complexes described by S.

Sigano provide impressive illustrations of this strategy in which the synthetic utility of carbenoid chemistry is coupled serially to a variety of pericyclic and metal-mediated reactions.

Lignin Biosynthesis and Structure | Plant Physiology

REDUCTIVE DEGRADATION OF LIGNIN IN SUPERCRITICAL SOLVENT AND APPLICATION IN PHENOLIC RESIN SYNTHESIS[J].

The interplay of biology, chemistry, medicine, and synthesis that attends much of natural products chemistry is also very much in evidence in this issue in exciting accounts of studies on the structurally and biochemically novel ellagitannins and pumiliotoxins covered by S.

The synthesis was enabled by a novel catalytic, enantioselective prototropic shift/furan Diels–Alder (IMDAF) cascade to construct the ACD tricyclic core.

Freudenberg K and Neish AC (1968) Constitution and Biosynthesis of Lignin. Berlin‐Heidelberg‐New York: Springer‐Verlag.
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    Radical Coupling Reactions in Lignin Synthesis: A Density Functional Theory Study Amandeep K

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    Radical Coupling Reactions in Lignin Synthesis: A Density Functional Theory Study

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lignin biodegradation with laccase-mediator ..

Resiniferatoxin (1) belongs to a daphnane diterpenoid family and has strong agonistic effects on TRPV1, a transducer of noxious temperature and chemical stimuli. The densely oxygenated -fused 5/7/6-tricarbocycle (ABC-ring) of 1 presents a daunting challenge for chemical synthesis. Here we report the development of a novel radical-based strategy for assembling 1 from three components: A-ring 9, allyl stannane 18b, and C-ring 17b. The 6-membered 17b, prepared from -ribose derivative 19, was designed to possess the caged orthoester structure with α-alkoxy selenide as a radical precursor. Upon treatment of 17b with 18b, 9, and V-40, the potently reactive α-alkoxy bridgehead radical was generated from 17b and then sequentially coupled with 9 and 18b to yield 16b. This first radical reaction formed the hindered C9,10-linkage between the A and C-rings and extended the C4-chain on the A-ring in a stereoselective fashion. After derivatization of 16b into 15, the remaining 7-membered B-ring was cyclized in the presence of -Bu3SnH and V-40 by utilizing the xanthate on the C-ring as the radical precursor and the allylic dithiocarbonate as the terminator. The second radical reaction thus enabled not only the 7- cyclization but also construction of the C8-stereocenter and the C6- olefin. Tricycle 14 was elaborated into the targeted 1 by a series of highly optimized chemoselective reactions. The present total synthesis of 1 demonstrates the advantages of radical reactions for linking hindered bonds within carbocycles without damaging preexisting functionalities, thereby offering a new strategic design for multistep target-oriented synthesis.

Mannich Reaction - Organic Chemistry Portal

Shigeru Yamago received his B.S. and Ph.D in chemistry from Tokyo Institute of Technology in 1986 and 1991, respectively, under the supervision of Professor Eiichi Nakamura. During that time, he joined Professor Peter Vollhardt’s group at U.C. Berkeley as a summer student (1988). He became an assistant professor at Tokyo Institute of Technology in 1991 in the group of Professor Eiichi Nakamura and then moved to Kyoto University in 1995 in the group of Professor Jun-ichi Yoshida. He was a Visiting Scientist in Dr. Chryssostomos Chatgilialoglu’s group at Consiglio Nazionale delle Ricerche in Bologna (2000). In 2003, he was appointed Professor of Osaka City University. He had been a Research Fellow of PRESTO program in the Japan Science and Technology Agency from 2002 to 2006. In 2006, he joined Institute for Chemical Research at Kyoto University where he holds Professorship. He received the Incentive Award in Synthetic Organic Chemistry from the Society of Synthetic Organic Chemistry, Japan, in 2001. His research interests include synthetic organic and polymer chemistry, radical chemistry, and element chemistry.

Cascade Radical Reactions in Organic Synthesis: ..

This breadth is reflected in part in the 24 reviews in this issue which include studies on reactive intermediates, organometallic chemistry, photochemistry, natural products chemistry, catalysis, solid-phase synthesis, chemical libraries, electrochemistry, novel materials, enzyme-mediated transformations, biochemistry, medicinal chemistry, biology, and virology.

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