Steps involved in synthesis

The book contains examples from recently published research work to illustrate the important steps involved in synthesis. The discussion is organized by the conditions under which the reaction is executed rather than by the types of mechanisms as is the case in most textbooks at the graduate level. 

FIG. 9 Reaction steps involved in synthesis of decyl sulfonate using phase transfer catalysis. 

The following short descriptions of the steps involved in the synthesis of a tripeptide will demonstrate the complexity of the problem amino acid units. In the later parts of this section we shall describe actual syntheses of well defined oligopeptides by linear elongation reactions and of less well defined polypeptides by fragment condensation. 

Show the steps involved in the synthesis of Ala-Leu from alanine and leucine using benzyloxycarbonyl and benzyl ester protecting groups and DCCI-promoted peptide bond formation. 

The steps involved in automated oligonucleotide synthesis illustrate the current use of protective groups in phosphate chemistry (Scheme 1). Oligonucleotide synthesis involves the protection and deprotection of the 5 -OH, the amino groups on adenine, guanine, and cytosine, and -OH groups on phosphorus. 

Show the steps involved in a synthesis of Phe-Ala-Val using the Merrifield procedure. 

A variety of compounds, including several antibiotics, inhibit protein synthesis by affecting one or more of the steps involved in protein synthesis. 

Scheme 2 The steps involved in the synthesis of the 5-HTia receptor ligands reported hy Paluchowska et al. (2002) [63], 1 PhsP, NBS, EtsN, CH2CI2, 0-25 °C 11 BOP, EtsN, CH3CN, rt 111 20% K2CO3 - CHCI3, rt IV xylene, reflux V pyridine, reflux... 

The tricyclic compound 20-C, a potential intermediate for alkaloid synthesis, has been prepared by an intramolecular Diels-Alder reaction of the ketone obtained by deprotection and oxidation of 20-B. Compound 20-B was prepared from 20-A using alkyne-ethene metathesis chemistry. Show the mechanistic steps involved in conversion of 20-A to 20-B. 

In preparation for scale-up of the strigol synthesis described by Sih (8), efforts were made to improve the yield of some of the seven steps involved in the scheme. Of these steps, nine are satisfactory from the standpoint of yield and experimental conditions. For three of the steps, we have improved the yield and/or experimental conditions such that the yield of (+ )-strigol would be raised to 2.85% overall from citral rather than 1.53% based on Sih s procedure and reported yields. Improvements were developed preparation of a-cyclocitral (III), the oxidation of the hydroxyaldehyde (V) to the ketoacid (VII), and for the preparation of the hydroxybutenolide (XVII). For the remaining five steps, our attempts to change experimental conditions have failed to improve, and in most cases to even obtain, the yields reported in the literature (8). We have considered the preparation of strigol analogs and determined the conditions and limitations for the preparation of a series of alkoxybutenolides (XVI) and a butenolide dimer (XVIII). Modification of the literature procedure (11) to eliminate the use of the mesylate (XX) and the use of polar aprotic solvents gave better yields of the 2-RAS (XXI). 

Synthesis and Characterization. Tris(trimethylsilylpropyl)tin fluoride (PTF) and tris(trimethylsilylmethyl)tin fluoride (MTF) were synthesized according to scheme A (Figure 1) while scheme B (Figure 1) was followed in the synthesis of dibutyl-(trimethylsilylpropyl)tin fluoride (BTF). MTF has been reported in the literature (6) however, it was synthesized to compare its solution properties with the other two novel compounds. The steps involved in these syntheses were straight-forward and thus need no elaboration. In the synthesis of BTF, the unsymmetrical triorganotin fluoride, bromination of tetraorganotin compound resulted... 

The steps involved in the synthesis are as follows D-glucose (XXII) was converted to l,2,3,4-tetraacetyl-6-trityl-D-glucose (XXIII) which by... 

The microspheres—synthesised via a two-step process (acid-catalysed hydrolysis and condensation of 3-mercaptopropyltrimethoxysilane (MPS) in aqueous solution, followed by condensation catalysed by triethanolamine)—have a narrow size distribution (Figure 5.16) and are considerably more stable than polystyrene divinylbenzene microspheres as shown in phosphoramidite oligonucleotide synthesis by the excellent retention of fluorescence intensity in each of the reagent steps involved in phosphoramidite DNA synthesis (Figure 5.17, in which the organo-silica microsphere free thiol groups are derivatized with ATTO 550 maleimide coupled to the entrapped dye). 

This chapter discusses the steps involved in the development and design of a new S02 oxidation catalyst VK69, which was introduced to the market in 1996 by Haldor Topsoe. The strategy and many of the methods are generally applicable to heterogeneous fixed bed catalysts, partly to fluid and slurry bed catalysts, and less relevant for homogeneous catalysts as found in organic synthesis and enzymatic reactions. 

Figure 3.25 Polymerase chain reaction. The steps involved in the chain reaction are as follows (i) Incubation of the DNA at a temperature above 90 °C in order to separate the two strands of the DNA duplex, (ii) Cooling of the solution to about 50 °C to allow annealing of the primers to the template (i.e. the nucleotides bind to the template DNA according to the basepairing rules), (iii) Finally, addition of the polymerase and Mg ions to extend the nucleotide primer and complete the synthesis of the complementary DNA, which takes place at about 70 °C. (iv) The sequence (i) to (iii) is repeated to allow another extension to occur many repetitions can be carried out which results in enormous multiplication of the DNA strands. NTPs - deoxyri-bonucleoside triphosphates.

Steps involved in the synthesis and metabolic degradation of serotonin. 

Fluorocorticoids are produced on the ton-scale (e.g., 1.1 tons of fluticasone in 2001). The industrial production of fluorocorticosteroids has been a triple chemical challenge availability of the starting material, use of hazardous and toxic fluorination reagents, and a large number of chemical or biotechnological steps involved in the synthesis, as highlighted by the synthesis of dexamethasone (Figure 8.45). 

The synthesis of allyl-functionalized octa-arm stars was achieved by a one-pot two-step procedure [64]. Scheme 6 shows the steps involved in the synthe-... 

The chemical steps involved in this synthetic scheme are somewhat similar to the ones described in a previous synthesis of 19-nor steroids.9... 

Other Claisen condensations are involved in synthesis of fatty acids and polyketides217 (Chapter 21) and in formation of 3-hydroxy-3-methylglutaryl-CoA, the precursor to the polyprenyl family of compounds (Chapter 22). In these cases the acetyl group of acetyl-CoA is transferred by a simple displacement mechanism onto an -SH group at the active site of the synthase to form an acetyl-enzyme.218 219 The acetyl-enzyme is the actual reactant in step b of Eq. 17-5 where this reaction, as well as that of HMG-CoA lyase, is illustrated. 

The Thil gene, which encodes aother sulfurtransferase protein, is also needed.3743 The enzymology of the insertion of this sulfur into the thiazole is uncertain but may resemble that involved in synthesis of biotin, lipoic acid, and molybdopterin.374 Linkage of the two parts of the thiamin molecule (step d, Fig. 25-21) is catalyzed by thiamin phosphate synthase, evidently via an SN2 type reaction.377-37713... 

Indicate the steps involved in the following synthesis of bicyclo[4.2.0]-2,4,6-octatriene (benzocyclobutene) ... 

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