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Laccase-Mediated Synthesis of Novel Antibiotics and Amino Acid Derivatives
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
The mechanism underlying the whole reaction is likely to be an intermediate laccase-catalyzed formation of the corresponding quinones and subsequent non-enzymatic amination with amines by Michael addition (Niedermeyer et al., 2005). The components of a Michael addition reaction include an activated a,ß-unsaturated molecule (acceptor; e.g., quinones) and a nucleophile (donor; e.g., amino groups of ß-lactam antibiotics) (Zhang and Mohanty, 2006). The carboxyl, the ester or amide groups of 2,5-dihydroxybenzoic acid and its derivatives draw electrons away from the quinone ring of the quinone intermediate corresponding to the -I- and -M-effect of carbonyl groups. In this way the quinone rings are activated towards nucleophiles, and the reaction rate of amination is high. Because of this these activated quinoid intermediates react fast with amino groups of ß-lactam antibiotics to heteromolecular products and transient quinoid intermediates have not been analyzed. In contrast, the carboxyl or the ester groups of 2,5-dihydroxyphenylacetic acid and its derivatives has a much lower electron withdrawing effect on the quinone ring. The quinone ring is much less activated towards nucleophiles, the reaction rate of amination is low, and the quinones of 2,5-dihydroxyphenylacetic acid methyl and ethyl ester have been detected as stable end products. The quinone of 2,5-dihydroxyphenylacetic acid is barely sufficiently activated to react with nucleophiles, e.g., amino groups of ß-lactam antibiotics to yield heteromolecular products.
Controlled Polymerization
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
As a specific example of a divergent synthesis, we will consider the formation of the polyamidoamine (PAMAM) system. In this case, there are two monomers to be added sequentially in each generation, rather than one addition and one deprotection step. The core molecule and one of the monomers is typically ethylene diamine and the other monomer is methyl acrylate. The first step is addition of four methyl acrylate molecules to ethylene diamine in a solvent such as methanol. The Michael addition-type mechanism involves nucleophilic attack of the electron pair on the nitrogen to the double bond of the acrylate, which is activated by the electron-withdrawing character of the ester group:
Enolate Anions and Condensation Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Michael addition is another term for 1,4-addition or conjugate addition of a nucleophile with a conjugated (α,β-unsaturated) ketone or aldehyde (usually a ketone) where the nucleophile adds to the π-bond of the alkene rather than to the carbonyl carbon. What is the initial product when a nucleophile reacts with methyl vinyl ketone?
Acetyl-protected cytosine and guanine containing acrylics as supramolecular adhesives
Published in The Journal of Adhesion, 2019
Keren Zhang, Gregory B Fahs, Evan Margaretta, Amanda G Hudson, Robert B Moore, Timothy E. Long
Michael addition serves as a versatile synthetic method in polymer chemistry for monomer synthesis, post-functionalization of polymers, or chemical cross-linking.[48] Michael addition of thymine or adenine with a diacrylate afforded regioselective synthesis of adenine/thymine acrylate monomers.[9] However, Michael addition of guanine with 1,4-butanediol diacrylate proved unsuccessful due to challenging solubility of guanine in common solvents. Acetyl protecting groups on the primary amines of cytosine and guanine increased their solubility, and subsequent Michael addition of acetyl-protected cytosine and guanine with excess diacrylate yielded N4-acetylcytosine acrylate (ACyA) and N2-acetylguanine acrylate (AGuA) (Figure 1), respectively. In both Michael addition reactions, the nucleobase suspension in DMSO turned clear as the Michael addition reached equilibrium with the majority of nucleobase converted to their acrylic monomers with enhanced solubility in most organic solvents. The disubstituted byproduct was removed during column chromatography. Protected guanine reacted with diacrylate on both the 7- and 9- position due to tautomerization.[49,50] The 9-AGuA isomer proves more polar than 7-AGuA, due to reduced steric effects of the acrylate group on the hydrogen bonding sites, while DNA only contains 9-substituted guanine.