Conformationally rigid pyrazoloquinazoline α-amino acids: one- and two-photon induced fluorescence

Abstract

Conformationally rigid unnatural α-amino acids bearing a pyrazoloquinazoline ring system that are amenable to both one- and two-photon excitation have been developed as new fluorescent probes.

Highly Fluorescent Dyes Containing Conformationally Restrained Pyrazolylpyrene (Pyrazoolympicene) Chromophore

“…Therefore, we became interested in the synthesis of conformationally restrained and planarized analogs of these compounds with the aim of batochromically shifting their emission maxima and improving their emission quantum yields. The bathochromic shift of the absorption and emission bands and the increase in the emission efficiency of the fluorophore resulting from the structural prevention of intramolecular rotations have already been demonstrated for various classes of dye [23][24][25] Herein, we disclose the synthesis of dyes 3 and 4 (Scheme 1), along with the study of their structures and optical properties, in comparison to those of 1 and 2.…”

Synthesis and Fluorescent Properties of Alkynyl- and Alkenyl-Fused Benzotriazole-Derived α-Amino Acids

“…The reaction mixture was stirred at room temperature for 0.5 h and concentrated in vacuo. Purification by trituration with chloroform gave (2S)-2-amino-3-{5′-[(4‴-dimethylaminophenyl)ethynyl]-1H-benzo [d][1.2.3]triazol-1′-yl}propanoic acid hydrochloride (12c) as a yellow oil (0.0300 g, 88%); IR (neat) 3406,2920,2361,1740,1694,1508,1211,1130,841 (d,1H,J = 8.5 Hz),7.93 (d,2H,J = 8.5 Hz),3H),2H) To a dry microwave vial containing zinc (0.0470 g, 0.720 mmol) and bis(triphenylphosphine)palladium(II) dichloride (0.0337 g, 0.0480 mmol), under argon, was added a solution of methyl (2S)-2-[(tertbutoxycarbonyl)amino]-3-[5′-(phenylethynyl)-1H-benzo [d][1.2.3]triazol-1′-yl]propanoate (11a) (0.100 g, 0.240 mmol) in tetrahydrofuran (1.2 mL). A 1 M solution of zinc iodide (0.240 mL, 0.240 mmol) in tetrahydrofuran was added and then the reaction mixture was degassed, purged with hydrogen, and stirred at 40 °C for 20 h. The reaction mixture was allowed to cool to room temperature and diluted with ethyl acetate (40 mL), washed with water (3 × 20 mL), dried (MgSO 4 ), and concentrated in vacuo.…”

Miniaturized Chemical Tags for Optical Imaging

“…[51] Alternative scaffolds have been successfully employed to prepare fluorescent amino acids with suitable properties for in vitro biomolecular and bioimaging studies (Figure 4). These include xanthone-based amino acids for studying peptide folding by triplet-triplet energy transfer, [52] acridon-2ylalanines for lifetime and Förster resonance energy transfer studies, [53] conformationally rigid pyrazoloquinazoline αamino acids for two-photon NIR excitation, [54] phospholyl and benzotriazoles amino acids with large Stokes shifts (> 160 nm), [55] and solvatochromic amino acids containing βpyridyl [56] or phthalimide groups for the preparation of environmentally sensitive peptides retaining bioactivity (e.g., transmembrane fragments of the epidermal growth factor receptor). [57] The miniaturized size of fluorescent amino acids has also been exploited to utilise the machinery of living cells for sitespecific labeling of proteins under physiological conditions.…”