Chemical Synthesis synthesizing

The chemical syntheses of l,24(R),25-trihydroxy-vitamiQ [56142-94-0] and l,24(3),25-trihydroxy-vitamiQ D [56142-95-1] were reported (131,132) ki 1975. The chemical synthesis of 25,26-dihydroxy-vitamin [29261 -12-9] has also been described, and it has been determined that the biologically occurring epimer is 25(R),26-dihydroxy-vitamin (117,133—135). The 23,25-dihydroxy-24-oxo metabohte has been isolated (136) as well. 1 a-Hydroxycalcitroic acid (l-hydroxy-24-nor-9,10-secochola-5,7-10(19)-ttien-23-oic acid) [71204-89-2], 25-hydroxy-26,23-lactone vitamin [71203-34-6],... 

Nucleic acids are the molecules of the genetic apparatus. They direct protein biosynthesis in the body and are the raw materials of genetic technology (see Genetic engineering). Most often polynucleotides are synthesized microbiologicaHy, or at least enzymatically, but chemical synthesis is possible. 

Chemically Synthesized Powders. Chemical synthesis provides a means of produciag powders for manufacturiag advanced ceramics. Disadvantages of chemically synthesized raw materials are expense and difficulties ia scale-up and availabihty. Additionally, ultrafine particle-size powders produced by chemical synthesis pose some unresolved processiag problems ia the areas of handling and mixing. 

A quick scan of the collection of structures in Part Three will confirm the high level of activity and accomplishment which has been associated with the field of chemical synthesis over the past three decades. Upon closer inspection, it becomes apparent that the rate of achievement of successful syntheses has been increasing steadily with time. As of this writing (1988) there are many laboratories in which outstanding work on multistep synthesis of complex molecules is being carried out. One consequence of this intense effort is that the problem of keeping track of the literature of synthesis has become a difficult one for investigators and students. The... 

There are a large number of naturally occurring molecules which have not yet been obtained by chemical synthesis. A convenient source of information on such compounds is The Dictionary of Organic Compounds, Fifth Addition (1982) and Supplements 1-5, published as a multivolume series by Chapman and Hall, New York and London J. Buckingham, Executive Editor. This compendium contains references to syntheses which are not included in this collection, especially those involving simpler target structures. 

There are many reasons for carrying out the laboratory synthesis of an organic compound. In the pharmaceutical industry, new organic molecules are designed and synthesized in the hope that some might be useful new drugs. In the chemical industry, syntheses are done to devise more economical routes to known compounds. In academic laboratories, the synthesis of complex molecules is... 

The term vitamin E describes a family of eight antioxidants, four tocopherols, alpha (a), beta ((3), gamma (y) and delta (8), and four tocotrienols (also a, (3, y, and 8). a-Tocopherol is present in nature in only one form, RRR a-tocopherol. The chemical synthesis of a-tocopherol results in eight different forms (SRR, SSR, SRS, SSS, RSR, RRS, RSS, RRR), only one of which is RRR a-tocopherol. These forms differ in that they can be right (R) or left (S) at three different places in the a-tocopherol molecule. RRR a-tocopherol is the only form of vitamin E that is actively maintained in the human body and is therefore the form of vitamin E found in the largest quantities in the blood and tissue. A protein synthesized in the liver (a-TTP alpha-tocopherol transfer protein) preferentially selects the natural form of vitamin E (RRR a-tocopherol) for distribution to the tissues. However, the mechanisms for the regulation of vitamin E in tissues are not known... 

The raw materials from which di-D-fructose dianhydrides can be obtained in appreciable yield are readily available from comparatively inexpensive agricultural feedstocks. Thus, these compounds are attractive as chiral-starting materials for chemical synthesis. Their stability to acid and heat, and their relative rigidity, because of the conformational constraints covered here, are also features that might be exploited during syntheses.119 A series of variously substituted di-D-fructose dianhydrides has been prepared,119 starting from 6,6 -dideoxy-6,6 -di-halosucroses. The properties of these and other derivatives of di-D-fructose dianhydrides are summarized in Tables XIV-XX. Two of these derivatives, 48 and 56, exhibit thermotropic liquid-crystal properties.119... 

Both the metal-atom and matrix techniques have many applications (91) in the study of complexes having such classical, inorganic ligands as CO, N2, O2, or phosphines. From a metal-atom point of view, novel complexes have been synthesized that have not been readily accessible via normal, chemical-synthesis techniques. The entrapment of such species permits both a rationalization of their spectroscopic and chemical properties and an evaluation of their stability. 

The automated chemical synthesis of moderately long oligonucleotides (about 100 nucleotides) of precise sequence is now a routine laboratory procedure. Each synthetic cycle takes but a few minutes, so an entire molecule can be made by synthesizing relatively short segments that can then be ligated to one another. Oligonucleotides are now indispensable for DNA se-... 

Li Q, Walter EC, van der Veer WE, Murray BJ, Newberg JT, Bohannan EW, Switzer JA, Hemminger JC, Penner RM (2005) Molybdenum disulfide nanowires and nanoribbons by electrochemical/chemical synthesis. J Phys Chem B 109 3169-3182 Tenne R, Homyonfer M, Feldman Y (1998) Nanoparticles of layered compounds with hollow cage structures (inorganic fuUerene-like structures). Chem Mater 10 3225-3238 Shibahara T (1993) Syntheses of sulphur-bridged molybdenum and tungsten coordination compounds. Coord Chem Rev 123 73-147... 

After identification of A9-THC as the major active compound in Cannabis and its structural elucidation by Mechoulam and Gaoni in 1964 [66], a lot of work was invested in chemical synthesis of this substance. Analogous to the biosynthesis of cannabinoids, the central step in most of the A9-THC syntheses routes is the reaction of a terpene with a resorcin derivate (e.g., olivetol). Many different compounds were employed as terpenoid compounds, for example citral [67], verbenol [68], or chrysanthenol [69]. The employment of optically pure precursors is inevitable to get the desired (-)-trans-A9-THC. 

Recent developments in DNA/RNA chemical synthesis have allowed us to attach some functional groups covalently to nucleic acids, thus permitting the introduction of a functionality or properties not normally present in the native biomolecule The use of non-nucleosidic linkers is probably the most popular approach for the 5 -terminal modification of chemically synthesized nucleic acid oligonucleotides and a number of such linkers are commercially available. The linker shown in Fig. 2 is designed as a phosphoramidate derivative so that it can be incorporated into the 5 -terminus of the sequence as the last... 

There is no other vitamin which exemplifies the interdependence between the human race and microorganisms better than Vitamin B12. Mankind still relies for its very existence upon the capability of a few species of bacteria to synthesize this fascinating coordination complex. A concerted effort is being made in a number of laboratories to determine procedures for the chemical synthesis of this vitamin. However, even the most talented synthetic chemists would have to admit that the organic chemist s lament is applicable to Vitamin B12 ... 

Lenhert and Hodgkin (15) revealed with X-ray diffraction techniques that 5 -deoxyadenosylcobalamin (Bi2-coenzyme) contained a cobalt-carbon o-bond (Fig. 3). The discovery of this stable Co—C-tr-bond interested coordination chemists, and the search for methods of synthesizing coen-zyme-Bi2 together with analogous alkyl-cobalt corrinoids from Vitamin B12 was started. In short order the partial chemical synthesis of 5 -de-oxyadenosylcobalamin was worked out in Smith s laboratory (22), and the chemical synthesis of methylcobalamin provided a second B 12-coenzyme which was found to be active in methyl-transfer enzymes (23). A general reaction for the synthesis of alkylcorrinoids is shown in Fig. 4. 

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