A practical approach for the preparation of monofunctional azulenyl squaraine dye

✍ Scribed by Wellington Pham; Ralph Weissleder; Ching-Hsuan Tung

• Book ID: 104253572
• Publisher: Elsevier Science
• Year: 2003
• Tongue: French
• Weight: 150 KB
• Volume: 44
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(03)00819-0

✦ Synopsis

The synthesis of monofunctional azulenyl squaraine dye NIRQ(700) is described. The essential azulene intermediate 3, 1-(methoxycarbonyl)-2-methylazulene, was achieved via [8+2] cycloaddition between lactone 2, 2H-3-methoxycarbonyl-cyclohepta[b]furan-2-one, and the in situ generated vinyl ethers under high temperature and pressure conditions. Methylation on the cycloheptatriene ring of 2-methyl azulene 6 via Meisenheimer-type intermediate following Schrott's method formed the carboxylic acid intermediate 9, 3-(2-methyl-azulen-4-yl)-propionic acid. Condensation of 9 with squaric acid provided the title compound NIRQ(700) at moderate yields. The non-fluorescent squaraine dye NIRQ(700) absorbed in a 600-700 nm range and potentially can be used to quench a number of available NIR fluorochromes in order to extend the spectrum of biological quenching assays.