The first example of a polyhedral boron derivative of gadolinium(III) phthalocyaninate as a promising prototype of a theranostic agent

Abstract

We report the first synthesis of a polyhedral boron derivative of gadolinium(III) phthalocyaninate. Initially, reaction of 4-nitrophthalonitrile with 4-formylphenol in the presence of base was carried out to give 4-(4-formylphenoxy)phthalonitrile. This compound was then converted to 4-(4-hydroxymethylphenoxy)phthalonitrile using sodium tris-acetoxy borohydride in THF. Sequential cyclotetramerisation of this semiproduct in the presence of magnesium acetate, treatment of the resulting complex with trifluoroacetic acid, and complexation with gadolinium(III) acetate afforded gadolinium(III) phthalocyanine containing four hydroxymethylphenoxy groups at the peripheral (β) positions. Then, a nucleophilic addition reaction of this complex with acetonitrilium derivative of [B10H10]2- anion afforded gadolinium(III) phthalocyaninate decorated with four closo-decaborate units in good/satisfactory yield. The new product was characterised by various techniques (CHN analysis, MALDI-TOF mass spectrometry and UV–Vis spectroscopy). The boron content in this product is 21.5 wt% (40 atoms), and the r1 relaxivity of the conjugate 6.1 ± 0.7 mM-1s−1 (at 3.0 T, 20 °C in water), which makes it a promising prototype for theranostic agents for MRI-guided BNC therapy in future investigations.