ABSTRACT
[Structure: See text] Double asymmetric [3 + 2]-annulation reactions of chiral beta-silyloxyallylsilanes with chiral 2-tetrahydrofuranyl carboxaldehydes have been studied, leading to the stereocontrolled synthesis of six diastereomeric bis-tetrahydrofuran structures corresponding to the core subunits of members of the Annonaceous acetogenin family of natural products. Transition-state models are proposed to account for the stereoselectivity of the double-stereodifferentiating [3 + 2]-annulation reactions.
Subject(s)
Aldehydes/chemistry , Allyl Compounds/chemistry , Fatty Alcohols/chemistry , Furans/chemical synthesis , Lactones/chemistry , Silanes/chemistry , Acetogenins , Chelating Agents , Furans/chemistry , Indicators and Reagents , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular ConformationABSTRACT
[reaction: see text] A total synthesis of (+)-bullatacin has been accomplished via a diastereoselective [3+2] annulation reaction of the highly enantiomerically enriched allylsilane 3 and racemic aldehyde 4, which provides the key bis-tetrahydrofuran fragment 15 with > or = 20:1 ds.
Subject(s)
Aldehydes/chemistry , Alkenes/chemistry , Furans/chemical synthesis , Silanes/chemistry , Boron/chemistry , Furans/chemistry , Hydroxylation , Kinetics , Molecular Structure , StereoisomerismABSTRACT
[reaction: see text] The protiodesilylation of unactivated C(sp3)-SiMe2Ph bonds proceeds efficiently by treatment with tetrabutylammonium fluoride in wet DMF or THF via isolable dimethylsilanol intermediates.
Subject(s)
Furans/chemistry , Quaternary Ammonium Compounds/chemistry , Silanes/chemistry , Molecular Structure , Structure-Activity RelationshipABSTRACT
In an effort to construct non-natural bases to be used in triplex-based antigene DNA recognition strategies, a uriedo-isoindolin-1-one homo-N-nucleoside base was designed to bind the cytosine-guanine (CG) base pair. An organic soluble analogue of this base was shown to effectively complex CG (K(assoc)=740M(-1)) in chloroform through formation of three hydrogen bonds (Mertz, E.; Mattei, S.; Zimmerman, S. C. Org. Lett. 2000, 2, 2931-2934). The novel nucleoside base was synthesized and successfully incorporated into oligonucleotides which were used in triple helix melting temperature studies. Low melting temperatures were observed when the isoindolin-1-one base was paired opposite CG as well as GC, TA, and AT, thus indicating that despite favorable recognition in model studies, the artificial base did not effectively recognize duplex DNA to form pyrimidine-purine-pyrimidine type triple helices.
Subject(s)
Cytosine/chemistry , DNA/chemistry , Guanine/chemistry , Indoles/chemical synthesis , Nucleic Acid Conformation , Oligonucleotides/chemistry , Oligonucleotides/chemical synthesis , Purine Nucleosides/chemistry , DNA/metabolism , Indoles/chemistry , Oligonucleotides/metabolism , Purines/chemistry , Pyrimidines/chemistry , ThermodynamicsABSTRACT
[reaction: see text] (Trifluoroacetyl)azobenzene dyes were previously employed as amine reporter groups (chemosensors) in a dendrimer-based monomolecular imprinting system. Kinetic and binding studies with a range of amines and diamines show that the highly selective signaling observed for alkane diamines by these imprinted dendrimers arises from a kinetic effect due to intramolecular general base-catalyzed carbinolamine formation with the dye itself. The relationship between diamine structure and carbinolamine stability and rate of formation is described.
Subject(s)
Amines/chemistry , Azo Compounds/chemistry , Diamines/chemistry , Hydrocarbons, Fluorinated/chemistry , Dimerization , Kinetics , Magnetic Resonance Spectroscopy/methods , Molecular Structure , Spectrophotometry/methods , ThermodynamicsABSTRACT
The integration of a chromogenic reporter group into the recently reported (Zimmerman, S. C.; Wendland, M. S.; Rakow, N. A.; Zharov, I.; Suslick, K. S. Nature 2002, 418, 399-403) monomolecular imprinting approach is described. The resulting highly cross-linked, macromolecular hosts show rapid, selective, high affinity, two-point binding of straight-chain diamine guests. Over longer times, the hosts are more promiscuous, binding a broader range of diamines. A rigorous test of imprinting was performed wherein the cross-reactivities of two dendrimers derived from different templates are compared. The test reveals a guest-dependent kinetic binding effect masquerading as evidence of a highly selective two-point imprinting process.
