60 research outputs found
Pyridines from azabicyclo[3.2.0]hept-2-en-4-ones through a proposed azacyclopentadienone
Pyridines have been formed by heating azabicyclo[3.2.0]hept-2-en-4-ones in toluene. The generation of a 3-azacyclopentadienone intermediate via a [2+2]-cycloreversion is proposed as the key step. A Diels-Alder reaction of a styrene, extrusion of carbon monoxide and loss of hydrogen then gives the pyridine. The process parallels the well-known synthesis of benzenes from cyclopentadienones. The azabicyclo[3.2.0]hept-2-en-4-ones were synthesized from the reaction between readily available cyclopropenones and 1-azetines, in which the cyclopropenones behave as all-carbon 1,3-dipolar equivalents
Fluorescein Analogue Xanthene-9-Carboxylic Acid: A Transition-Metal-Free CO Releasing Molecule Activated by Green Light
Cyclopropenone-caged Sondheimer diyne (dibenzo[a,e]cyclooctadiyne): a photoactivatable linchpin for efficient SPAAC crosslinking
Enhancement of the Reactivity of Photochemically Generated Enediynes via Keto−Enol Tautomerization
Fluorophore Targeting to Cellular Proteins via Enzyme-Mediated Azide Ligation and Strain-Promoted Cycloaddition
Methods for targeting of small molecules to cellular
proteins can
allow imaging with fluorophores that are smaller, brighter, and more
photostable than fluorescent proteins. Previously, we reported targeting
of the blue fluorophore coumarin to cellular proteins fused to a 13-amino
acid recognition sequence (LAP), catalyzed by a mutant of the Escherichia coli enzyme lipoic acid ligase (LplA).
Here, we extend LplA-based labeling to green- and red-emitting fluorophores
by employing a two-step targeting scheme. First, we found that the
W37I mutant of LplA catalyzes site-specific ligation of 10-azidodecanoic
acid to LAP in cells, in nearly quantitative yield after 30 min. Second,
we evaluated a panel of five different cyclooctyne structures and
found that fluorophore conjugates to aza-dibenzocyclooctyne (ADIBO)
gave the highest and most specific derivatization of azide-conjugated
LAP in cells. However, for targeting of hydrophobic fluorophores such
as ATTO 647N, the hydrophobicity of ADIBO was detrimental, and superior
targeting was achieved by conjugation to the less hydrophobic monofluorinated
cyclooctyne (MOFO). Our optimized two-step enzymatic/chemical labeling
scheme was used to tag and image a variety of LAP fusion proteins
in multiple mammalian cell lines with diverse fluorophores including
fluorescein, rhodamine, Alexa Fluor 568, ATTO 647N, and ATTO 655
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