Orthogonally Protected Diaminoterephthalate Scaffolds: Installation of Two Functional Units at the Chromophore

Abstract

The 2,5-diaminoterephthalate structural motif is a powerful chromophore with remarkable fluorescence properties. Containing two carboxylate and two amino functions, it defines a colored molecular scaffold which allows for orthogonal functionalization with different functional units. Therefore, different applications in life sciences and materials science could be addressed. In this study, the two amino functions were alkylated by reductive amination with side chains carrying amino (orthogonally protected as Boc or Alloc) and carboxylate functions (orthogonally protected as tBu or allyl ester). After sequential deprotections, functional units were introduced by amidation reactions. As three examples, the chromophore was coupled with retinoic acid and fullerene C in order to obtain a triad for studying photoinduced electron transfer processes. Furthermore, cyclooctyne and azide moieties were introduced as functional units, allowing for ligation by click reactions. These two clickable groups were applied in combination with maleimide units which are reactive toward thiol residues. The latter dyes define so-called "turn on" probes, since the fluorescence quantum yields increased by one order of magnitude upon reaction with the molecular target.

Electron Transfer and Electron Excitation Processes in 2,5‐Diaminoterephthalate Derivatives with Broad Scope for Functionalization

“…The preparation of products 3 and 4 started from compound 12 (Scheme ), which was accessed from compound 8 in two steps (reductive amination with N ‐Alloc‐3‐aminopropanal and subsequent N ‐Boc‐deprotection) as reported recently . Reductive amination with trifluoromethylated benzaldehyde 9 was accomplished as above and furnished product 4 in 93 % yield.…”

“…Complete synthetic procedures as well as spectroscopic characterization can be found in the Electronic Supporting Information (ESI). The preparation of starting materials 8 and 12 was recently reported …”

Diaminoterephthalate–α-lipoic acid conjugates with fluorinated residues

“…In order to achieve a bathochromic shift of absorption and emission bands, the DAT and ALA moieties should be electronically decoupled by introduction of a propylene spacer. Therefore, we started the synthesis with compound 5 (Scheme 2), which was accessed from compound 1 in two steps by reductive amination with N -Alloc-3-aminopropanal and subsequent N -Boc deprotection as reported recently [44]. Reductive amination with trifluoromethylated benzaldehyde was accomplished as described for compound 2 and furnished product 6 in 91% yield.…”

“…UV–vis spectra were recorded with a Shimadzu UV-1800, fluorescence spectra with a Shimadzu RF-5301PC spectrometer. Compounds 1 [41] and 5 [44] were prepared according to literature procedures. All other starting materials were commercially available.…”

“…Diethyl 2-( tert -butoxycarbonyl)amino-5-[4-(trifluoromethyl)benzylamino]terephthalate (2): In a similar manner as described in [44], a solution of DAT 1 (0.567 mmol, 200 mg, 1.0 equiv) in CH 2 Cl 2 (3 mL) was added dropwise to a cooled (ice-water bath) suspension of 4-(trifluoromethyl)benzaldehyde (0.850 mmol, 148 mg, 1.5 equiv) in CH 2 Cl 2 (3 mL). After stirring the mixture for 15 min at ambient temperature, it was cooled (ice-water bath) and ZnCl 2 (0.23 mmol, 39 mg, 0.5 equiv) and NaBH 3 CN (0.85 mmol, 53 mg, 1.5 equiv) were added.…”