8th International Electronic Conference on Synthetic Organic Chemistry. ECSOC-8. 1-30 November 2004. http://www.lugo.usc.es/~qoseijas/ECSOC-8/  

[A018]

SYNTHESIS OF FLUORESCENT BENZO[a]PHENOXAZINES

 

Vânia H. J. Frade, M. Sameiro T. Gonçalves* and João C.V.P. Moura

 

Centro de Química, Universidade do Minho, Gualtar, 4710-057 Braga, Portugal

[email protected]

 

Introduction

         Among the applications of fluorescent synthetic dyes in biology, labelling of important molecules such as DNA, proteins and drugs has seen a remarkable growth in research interest and technical importance.1-5

         Fluorescence spectroscopy is an extremely sensitive technique. Although there are large number of fluorescent dyes commercially available, few are long-wavelength light-emiting dyes (600-1000 nm), a highly requiring operating region where there is minimum interference from absorption scattering and from the sample’s natural auto fluorescence of biological molecules.6

         Having this in mind, the present work reports the efficient synthesis of several benzo[a]phenoxazines dyes 1 with visible absorption in the 500-638 nm region and fluorescence with emission wavelength higher than 600 nm.

 

 

Results and Discussion

   Benzo[a]phenoxazine  dyes 1 were prepared according to classical method7 by the reaction of 5-alkylamino-2-nitrosophenol hydrochloride 2, with N-alkylated-naphthylamine 3 in acidic medium (Scheme 1). The required 5-alkylamino-2-nitrosophenol  hydrochloride 2 was synthesised by usual procedure involving treatment of the 3-alkylaminophenol with sodium nitrite in acid solution. N-Alkyl-naphthylamines 3a-b were prepared by acylation of 1-naphthylamine with chloropropionic acid and 3-ethyl-3-bromopropionate, respectively. After purification by dry chromatography, these compounds were obtained as off-white solid (3a, 48%) and oil (3b, 45%) and characterised by high resolution mass spectrometry, IR and NMR (1H and 13C) spectroscopy. The presence of the carbonyl group is confirmed by IR, which shows a strong band at 1717 (3a) and 1725 (3b) cm-1. In the 13C NMR, signals at d 164.4 and 172.5 ppm were assigned to the functional group.

         When compound 2a reacted with 3a, reflux in methanol, benzo[a]phenoxazine 1a was isolated by dry chromatography purification as the major product (77%). Although esterification occurred, the carboxylic acid derivative (1b) was also obtained in 22%. Starting with 5-diethyl-2-nitrosophenol hydrochloride (2b) both dyes 1c and 1d were obtained in 64 and 7% yield, respectively. Reaction of compounds 2b and 2c with alkylated naphthylamine 3b and under the same conditions reported above led to benzo[a]phenoxazine 1e (97%) and 1f (90%) (Table 1).

           

Scheme 1

        

All dyes were obtained as blue materials and were fully characterised by elemental analysis or high resolution mass spectrometry, IR, NMR (1H and 13C) and visible spectroscopy.

         The visible spectra of compounds 1 showed absorption peaks between 500 (1a) and 638 (1c) nm with e values ranging from 12075 (1b) to  43030 (1c)  (Table 1). 

 

 

Table 1. Yields and Vis data for compounds 1.

Compound

Yield/ %

Visa/ lmax[nm] (e)

1a

77

500 (24667)

1b

22

625 (12075)

1c

64

638 (43030)

1d

7

635 (22458)

1e

97

633 (22615)

1f

90

630 (29798)

aSpectra were run in absolute ethanol.

 

Studies of the fluorescent properties of the novel benzo[a]phenoxazine are on the way and preliminary results showed that all compounds exhibit fluorescence with emission wavelength higher than 600 nm.

         Considering the visible absorption and the potential fluorescence and also their water solubility these compounds are expected to be good probes for biological applications.

 

Acknowledgments

We thank the Fundation for Science and Technology (Portugal) for financial support to the Centro de Química (University of Minho).

 

References

1. Y. Lin, T. Chiu, H. Chang, J. Chromatogr. B, 2003, 793, 37-48.

2. S. Mittoo, L.E. Sundstrom and M. Bradley, Anal. Biochem., 2003, 319, 234-238.

3. R. Gatti, M.G. Gioia, P. Andreatta and G. Pentassuglia, J. Pharm. Biomed. Anal., 2004, 35, 339-348.

4. J.Z. Yang, K.C. Bastian, R.D. Moore, J.F. Stobaugh and R.T. Borchardt, J. Chromatogr. B, 2002, 780, 269-281.

5. R. Gatti, M.G. Gioia and A.M. Di Pietra, Anal. Chim. Acta, 2002, 474, 11-20.

6. R.P. Haugland, Handbook of Fluorescent Probes and Research Products, 9th ed., Molecular Probes, Eugene, OR, 2002.

7. M.L. Crossley, P.F. Dreisbach, C.M. Hofmann and R.P. Parker, J. Am. Chem. Soc., 1952, 74 (5), 573-578.