Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Abstract

Two novel derivatives of 2,3-diazabicyclo[2.2.2]oct-2-ene were synthesized, carrying a carboxyl (4) and a methylcarboxyl (5) substituent at the bridgehead position. The photodecomposition quantum yields (51% for 4 and 2.9% for 5) and fluorescence lifetimes (29 ns for 4 and 345 ns for 5) in water were determined. The higher photoreactivity and fluorescence quenching for 4 was attributed to its higher propensity to undergo photochemical elimination of nitrogen as a consequence of the presence of the radical-stabilizing carboxyl group in the α-position. The absolute photodecomposition rate constants of 4 became faster upon protonation (e.g., at pH 2), which contrasted anticipated substituent effects on the C-N bonds strengths. ) which was attributed to reduced Coulomb attractions as a consequence of the 1,3-alternate conformation which this host adopts in water. The binding constants towards β-cyclodextrin were also low at pH 7.0 (< 120 M -1 ), which was attributed to the low hydrophobicity of the anionic form of the guests; in line with this interpretation, the binding constants with β-cyclodextrin increased at pH 2.0, by about one order of magnitude.

Single-Label Kinase and Phosphatase Assays for Tyrosine Phosphorylation Using Nanosecond Time-Resolved Fluorescence Detection

“…DBO has been subject to extensive photophysical investigations, − and has recently found diverse applications in supramolecular − and biomolecular chemistry, ,,,,,,− including its use in peptides 21-23,32,38,46-53 and enzyme assays. ,,,, The DBO chromophore stands alone due to its exceedingly long fluorescence lifetime of up to 1 μs in the gas phase and 320 ns in aerated water, ,,,, which enables the efficient suppression of background fluorescence 22 and an increased differentiation of product vs substrate by Nano-TRF detection . In essence, the fluorescence can be measured after a sufficiently long time delay in the nanosecond range, e.g., after 150 or 500 ns.…”

“…DBO has been subject to extensive photophysical investigations, [28][29][30][31][32][33][34][35][36][37] and has recently found diverse applications in supramolecular [37][38][39][40][41][42][43][44][45] and biomolecular chemistry, 20,21,29,35,36,40,[43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] including its use in peptides [21][22][23]32,38,[46][47][48][49][50][51]…”

Theoretical Analysis of Reactivity Patterns in Diels–Alder Reactions of Cyclopentadiene, Cyclohexadiene, and Cycloheptadiene with Symmetrical and Unsymmetrical Dienophiles

“…The hetero-Diels–Alder reactions of both N -phenyl-1,2,4-triazolin-3,5-dione (PTAD) and nitrosobenzene with all three cyclic dienes, however, occur readily under mild conditions, as shown in Scheme . − …”

1,3-Cyclohexadien-1-Als: Synthesis, Reactivity and Bioactivities

“…Oxidation of the aldehyde group in 1,3-cyclohexadien-1-carboxaldehyde to the carboxylic acid has been achieved with silver hydroxide prepared in situ ( Scheme 47 ) [ 78 ]. Compound 203 was used in the cycloaddition reaction with 4- N -methyl-1,2,4-triazolin-3,5-dione 204 .…”

“…Oxidation of the aldehyde group in 1,3-cyclohexadien-1-carboxaldehyde to the carboxylic acid has been achieved with silver hydroxide prepared in situ (Scheme 47) [78]. Compound 203 was used in the cycloaddition reaction with 4-N-methyl-1,2,4-triazolin-3,5dione 204. depicts a (4 + 2) and (3 + 3) cycloaddition of α,β-unsaturated aldehydes mediated by Lproline 131 or pyrrolide 129/acetic acid (AcOH) to afford the cyclohexadiene carboxaldehyde intermediate that was not isolated and spontaneously oxidize or directly submitted to oxidation reaction conditions with MnO2 or DDQ for the formation of the aromatic compound [62].…”