ABSTRACT
The synthesis and conformational analysis of a new type of conformationally restricted alpha-amino acid analogue of the amino acid antibiotic furanomycin is presented. The restriction involves the cis-fused cyclobutane and tetrahydrofuran units, generating the unusual 2-oxabicyclo[3.2.0]heptane core, which is found in a great number of biologically active natural products. The synthetic strategy is based on a formal [2 + 2] cycloaddition between 2-(acylamino)acrylates as acceptor alkenes and 2,3-dihydrofuran as a donor alkene, promoted by bulky aluminum-derived Lewis acids, particularly by methylaluminoxane (MAO). Additionally, following the same strategy, the synthesis of furanomycin analogues incorporating the 2-oxabicyclo[4.2.0]octane is reported.
Subject(s)
Aluminum Compounds/chemistry , Amino Acids/chemistry , Amino Acids/chemical synthesis , Cyclobutanes/chemical synthesis , Catalysis , Crystallography, X-Ray , Cyclization , Cyclobutanes/chemistry , Magnetic Resonance Spectroscopy , Molecular Conformation , Stereoisomerism , Structure-Activity RelationshipABSTRACT
Quantitative NMR can be used to monitor several processes that take place in the transformation of the must of wine grapes. The study described here focused attention on monitoring of the malic and lactic acid levels during the alcoholic and malolactic fermentation processes. The method allows the simultaneous quantification of both acids through a range of 1-3.2 mmol/L. The effectiveness of each process was assessed and compared by carrying out precise analyses using enzymatic methods.
Subject(s)
Fermentation , Lactic Acid/analysis , Magnetic Resonance Spectroscopy , Malates/analysis , Vitis/chemistry , Wine/analysis , Kinetics , Lactic Acid/metabolism , Malates/metabolismABSTRACT
A formal [2 + 2] cycloaddition of 2-amidoacrylates with monosubstituted donor olefins, including its asymmetric version, is described. The stereoselectivity of this reaction can be modulated by the use of sterically hindered aluminum aryloxides or methylaluminoxane as Lewis acids. The reaction was applied to the synthesis of both stereoisomers of 2-benzyloxycyclobutane-alpha-amino acid, which are protected serine analogues c(4)Ser(OBn).
Subject(s)
Amino Acids/chemical synthesis , Serine/analogs & derivatives , Serine/chemical synthesis , Alkenes/chemistry , Aluminum/chemistry , Amino Acids/chemistry , Molecular Structure , Serine/chemistry , StereoisomerismABSTRACT
In this paper, we describe a thermal [2 + 2] cycloaddition involving 2-acylaminoacrylates as electron-poor acceptor alkenes, a reaction that involves a Michael-Dieckmann-type process. The reaction gives rise to a new substituted cyclobutane skeleton that can be transformed into amino acid derivatives. For example, a number of transformations were carried out to give the two pairs of stereoisomers of the 2-hydroxycyclobutane-alpha-amino acid serine analogue (c(4)Ser); compounds 22 and 23. This synthesis covers a gap in knowledge in the broad field of restricted amino acids.
Subject(s)
Cyclobutanes/chemical synthesis , Serine/analogs & derivatives , Serine/chemical synthesis , Catalysis , Cyclobutanes/chemistry , Indicators and Reagents , Magnetic Resonance Spectroscopy , Molecular Structure , Stereoisomerism , ThermodynamicsABSTRACT
The reactivity of 2-acylaminoacrylates with ketene diethyl acetal can be modulated by means of thermal conditions to yield cyclobutanes for the preparation of protected beta-hydroxycyclobutane-alpha-amino acids, or catalytic conditions that yield cyclohexanes by tandem condensations to obtain interesting building blocks that are alternatives to Danishefsky's diene.