Natural heterocyclic polymers chemistry

Olefin metathesis reaction that reorganizes carbon-carbon double bonds provides fundamentally new strategies for natural product synthesis and polymer chemistry. Hilvert and coworkers built up an artificial metalloenzyme by covalently tethering a Grubbs-Hoveyda-type Ru complex to a protein scaffold [78]. An /V-heterocyclic carbene (NHC) ligand, which has been reported as a suitable ligand for a number of water-soluble ruthenium-based metathesis catalysts, was derivatized with an electrophilic bromoacetamide. The Ru carbene complex (27 in Figure 10.16) was then attached by site-selective alkylation of the cysteine... 

After an inordinately long induction period, organopalladium chemistry has finally been embraced by synthetic organic chemists. Currently, it is being utilized across the spectrum of organic synthesis, from applications to complex natural product syntheses to the synthesis of polymers. A substantial portion of organopalladium methodology has been developed in the context of heterocyclic chemistry and applications to heterocyclic syntheses abound. 

Saturated six-membered heterocyclic rings can be found in various fields of chemistry, e.g., natural products, drugs and polymers. Representative molecules are cyclohexane derivatives in which ring methylenes are either substituted by alkyl or other functional groups or replaced by one or more heteroatoms (mainly nitrogen, oxygen, and sulfur). 

Whereas natural monomers like terpenes and sugars constitute building blocks for a limited number of macromolecular structures, associated with their own peculiar chemical features, the realm of furan polymers bears a qualitatively different connotation in that it resembles the context of petrol refinery, that is, it is open to a whole domain of monomers, whose only specificity is the fact that they all incorporate the furan heterocycle in their structure. This state of affairs stems from the fact that, as in petroleum chemistry, saccharide-based renewable resources are used to produce two first-generation furan derivatives, which constitute the substrates capable of being converted into a vast array of monomers and hence a correspondingly large number of macromolecular structures associated with materials possessing different properties and applications [34]. 

The chemistry of oxazoles continues to be an important focus of academic and industrial laboratories around the world. Indeed, this small-ring heterocycle has elicited extraordinary creativity from medicinal and process chemists, polymer chemists, materials scientists, photographic dye chemists, and natural products chemists engaged in basic and applied research. 

Indole is perhaps the most visible heterocycle in all of chemistry. Since Adolf von Baeyer proposed the structure of indole as a heteroaromatic compound 140 years ago, indole has embodied a myriad of natural products, pharmaceutical agents, and a growing list of polymers. In the human body, serotonin modulates 5-hydroxytryptamine (5-HT), a monoamine neurotransmitter primarily found in the gastrointestinal (GI) tract and central nervous system (CNS), and modulates vasoconstriction and many brain activities. Melatonin regulates circadian rhythms, most noticeably, sleep. Tryptamine is closely related to melatonin and the amino acid tryptophan. 

Furan derivatives are ubiquitous in nature in a wide variety of structures, but all of them appear in very modest amounts within specific vegetable and animal (including human) species. The interest of these compounds is mostly relevant to phytochemists and other natural product practitioners [1]. The chemistry associated with the furan heterocycle has been the subject of extensive studies over the last century and is sill a very active field of research because of its important repercussions in areas such as synthons, pharmaceuticals and other fine chemicals [2], liquid crystals [3], as well as polymer science and technology [4]. The classic treatise by Dunlop and Peters [5], which placed furan chemistry in a highly visible perspective, was followed by a number of comprehensive reviews and monographs which progressively updated the state of the art [1-4]. 

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