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Short Note

Rhodamine B Pentyl Ester and its Methyl, Ethyl, Propyl, and Butyl Homologues

by
Justin A. Ross
1,*,
Benjamin P. Ross
2,3,
Kelly L. Cosgrove
2,
Halina Rubinsztein-Dunlop
1 and
Ross P. McGeary
2,3
1
ACentre for Biophotonics and Laser Science, School of Physical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
2
School of Molecular and Microbial Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
3
School of Pharmacy, The University of Queensland, Brisbane, Queensland 4072, Australia
*
Author to whom correspondence should be addressed.
Molbank 2006, 2006(6), M515; https://doi.org/10.3390/M515
Submission received: 22 June 2006 / Accepted: 11 August 2006 / Published: 1 December 2006
Browse Figure
Versions Notes

Molbank 2006 m515 g001
The rhodamines are a highly fluorescent class of compound used in many different fields of research, from the lasing medium in dye lasers to biological stains and markers for cellular drug resistance [1,2,3]. We are interested in the influence of lipophilicity on the transport of esters of rhodamine in multidrug resistance transporter assays. Herein we describe the synthesis of the novel compound rhodamine B pentyl ester (2), and deposit the spectral data of the known methyl (3), ethyl (4), propyl (5), and butyl (6) homologues [4]. Ester 2 was prepared by a slightly modified facile method [5] that utilizes anhydrous hydrogen chloride generated in situ by the addition of AcCl to a mixture of the rhodamine B free acid (1) and n-pentanol.

Rhodamine B pentyl ester (2)

N-[6-(Diethylamino)-9-[2-(pentyloxycarbonyl)phenyl]-3H-xanthen-3-ylidene]-N-ethylethanaminium chloride

Acetyl chloride (1.25 mL, 17.6 mmol) was added dropwise to a stirred mixture of rhodamine B (1, 100 mg, 0.21 mmol) and n-pentanol (25 mL), and the reaction was heated at 50°C under an atmosphere of argon. After 2 days the reaction was ~ 90% complete by TLC, and additional acetyl chloride (250 µL, 3.52 mmol) was added to drive the reaction to completion. After a further 24 h TLC indicated no remaining rhodamine B (1) and the solution was evaporated in vacuo (water bath temperature < 50 °C to avoid degradation of the product) to afford rhodamine B pentyl ester (2), which was contaminated with a small amount of n-pentanol. The molar ratio of rhodamine B pentyl ester (2):n-pentanol was ~ 3:1 by 1H NMR. To separate the ester (2) from residual alcohol, the crude product was dissolved in water (100 mL) and washed with ethyl acetate (3 × 50 mL). Acetonitrile (35 mL) was added to the aqueous layer and this solution was lyophilised to afford the title compound (2), a hygroscopic amorphous solid (85%).
TLC Rf 0.41 (silica gel 60 F254 aluminum sheets, n-butanol:water:ethanol 9:2:1).
ES-MS, m/z: 513 [M+H]+.
1H NMR (500 MHz, d6-DMSO) δ 8.24 (1H, dd, J = 7.9 and 1.2 Hz), 7.91 (1H, dt, J = 7.5 and 1.3 Hz), 7.85 (1H, dt, J = 7.7 and 1.3 Hz), 7.51 (1H, dd, J = 7.5 and 1.1 Hz), 7.11 (2H, dd, J = 9.6 and 2.4 Hz), 7.02-6.99 (4H, m), 3.89 (2H, t, J = 6.2 Hz), 3.65 (8H, br q, J = 7.1 Hz), 1.20 (12H, br t, J = 7.0 Hz) overlapping with ~1.18-1.13 (2H, m), 1.06 (2H, sextet, J = 7.4 Hz), 0.88-0.82 (2H, m), 0.71 (3H, t, J = 7.4 Hz).
13C NMR (100 MHz [6], d6-DMSO) δ 165.1, 157.6, 157.1, 155.1, 133.0, 132.7, 131.0, 130.9, 130.5, 130.4, 129.9, 114.6, 112.9, 95.9, 65.2, 45.3, 27.5, 27.4, 21.7, 13.6, 12.4.
UV-visible (H2O): λmax 559 nm.
HRMS calcd for [M+H]+ 513.3117, found 513.3122.
The methyl (3), ethyl (4), propyl (5) and butyl (6) homologues of 2 were synthesized by the same method except that evaporation of the solution in vacuo afforded the ester (3-6) pure, without the need for partitioning between water and ethyl acetate. Previously these compounds were isolated as the bromide, iodide or perchlorate salts, and their spectra were recorded in CDCl3 [4]. Herein we deposit the spectra of the chloride salts (3-6) recorded in d6-DMSO.

Rhodamine B methyl ester (3)

N-[6-(Diethylamino)-9-[2-(methoxycarbonyl)phenyl]-3H-xanthen-3-ylidene]-N-ethylethanaminium chloride

TLC Rf 0.35 (silica gel 60 F254 aluminum sheets, n-butanol:water:ethanol 9:2:1).
ES-MS, m/z: 457 [M+H]+.
1H NMR (500 MHz, d6-DMSO) δ 8.27 (1H, dd, J = 7.9 and 1.2 Hz), 7.92 (1H, dt, J = 7.6 and 1.3 Hz), 7.84 (1H, dt, J = 7.7 and 1.3 Hz), 7.51 (1H, dd, J = 7.5 and 1.1 Hz), 7.08 (2H, dd, J = 9.6 and 2.5 Hz), 6.99-6.97 (4H, m), 3.65 (8H, br q, J = 7.02 Hz), 3.60 (3H, s), 1.21 (12H, br t, J = 7.0 Hz).
13C NMR (75 MHz, d6-DMSO) δ 165.0, 157.9, 157.1, 155.1, 133.4, 133.3, 130.8, 130.8, 130.5, 130.5, 129.2, 114.6, 112.8, 95.9, 52.5, 45.3, 12.5.
UV-visible (H2O): λmax 558 nm.
HRMS calcd for [M+H]+ 457.2491, found 457.2481.

Rhodamine B ethyl ester (4)

N-[6-(Diethylamino)-9-[2-(ethoxycarbonyl)phenyl]-3H-xanthen-3-ylidene]-N-ethylethanaminium chloride

TLC Rf 0.37 (silica gel 60 F254 aluminum sheets, n-butanol:water:ethanol 9:2:1).
ES-MS, m/z: 471 [M+H]+.
1H NMR (500 MHz, d6-DMSO) δ 8.25 (1H, dd, J = 7.9 and 1.1 Hz), 7.91 (1H, dt, J = 7.6 and 1.4 Hz), 7.84 (1H, dt, J = 7.7 and 1.2 Hz), 7.52 (1H, dd, J = 7.6 and 1.1 Hz), 7.09 (2H, dd, J = 9.6 and 2.5 Hz), 7.01-6.99 (4H, m), 3.98 (2H, q, J = 7.1 Hz), 3.65 (8H, br q, J = 7.0 Hz), 1.21 (12H, br t, J = 7.0 Hz), 0.90 (3H, t, J = 7.1 Hz).
13C NMR (75 MHz, d6-DMSO) δ 164.7, 157.7, 157.1, 155.1, 133.1, 133.0, 130.9, 130.7, 130.5, 130.4, 129.7, 114.6, 112.9, 95.9, 61.0, 45.4, 13.4, 12.4.
UV-visible (H2O): λmax 559 nm.
HRMS calcd for [M+H]+ 471.2648, found 471.2643.

Rhodamine B propyl ester (5)

N-[6-(Diethylamino)-9-[2-(propoxycarbonyl)phenyl]-3H-xanthen-3-ylidene]-N-ethylethanaminium chloride

TLC Rf 0.39 (silica gel 60 F254 aluminum sheets, n-butanol:water:ethanol 9:2:1).
ES-MS, m/z: 485 [M+H]+.
1H NMR (500 MHz, d6-DMSO) δ 8.25 (1H, dd, J = 7.8 and 1.2 Hz), 7.91 (1H, dt, J = 7.6 and 1.3 Hz), 7.85 (1H, dt, J = 7.7 and 1.2 Hz), 7.52 (1H, dd, J = 7.5 and 1.0 Hz), 7.09 (2H, dd, J = 9.6 and 2.5 Hz), 7.02-6.99 (4H, m), 3.89 (2H, t, J = 6.4 Hz), 3.65 (8H, br q, J = 7.0 Hz), 1.29 (2H, sextet, J = 6.9 Hz), 1.20 (12H, br t, J = 7.0 Hz), 0.62 (3H, t, J = 7.4 Hz).
13C NMR (75 MHz, d6-DMSO) δ 164.9, 157.7, 157.1, 155.1, 133.1, 132.9, 130.9, 130.8, 130.5, 130.4, 129.8, 114.6, 112.9, 95.9, 66.7, 45.4, 21.1, 12.4, 10.0.
UV-visible (H2O): λmax 559 nm.
HRMS calcd for [M+H]+ 485.2804, found 485.2801.

Rhodamine B butyl ester (6)

N-[6-(Diethylamino)-9-[2-(butoxycarbonyl)phenyl]-3H-xanthen-3-ylidene]-N-ethylethanaminium chloride

TLC Rf 0.40 (silica gel 60 F254 aluminum sheets, n-butanol:water:ethanol 9:2:1).
ES-MS, m/z: 499 [M+H]+.
1H NMR (500 MHz, d6-DMSO) δ 8.24 (1H, dd, J = 7.9 and 1.2 Hz), 7.91 (1H, dt, J = 7.5 and 1.4 Hz), 7.84 (1H, dt, J = 7.7 and 1.4 Hz), 7.51 (1H, dd, J = 7.6 and 1.1 Hz), 7.10 (2H, dd, J = 9.6 and 2.5 Hz), 7.02-7.00 (4H, m), 3.91 (2H, t, J = 6.2 Hz), 3.65 (8H, br q, J = 7.2 Hz), 1.21 (12H, br t, J = 7.0 Hz) overlapping with ~1.20-1.15 (2H, m), 0.94 (2H, sextet, J = 7.6 Hz), 0.68 (3H, t, J = 7.4 Hz).
13C NMR (75 MHz, d6-DMSO) δ 165.0, 157.5, 157.1, 155.1, 133.0, 132.7, 130.9, 130.7, 130.4, 130.3, 129.8, 114.6, 112.8, 95.8, 64.9, 45.3, 29.8, 18.4, 13.4, 12.4.
UV-visible (H2O): λmax 559 nm.
HRMS calcd for [M+H]+ 499.2961, found 499.2973.

Supplementary materials

Supplementary File 1Supplementary File 2Supplementary File 3

Acknowledgments

We thank Mr. Graham MacFarlane (School of Molecular and Microbial Sciences, The University of Queensland) for accurate mass measurements. This work was supported by funds from the Centre for Biophotonics and Laser Science, School of Physical Sciences, The University of Queensland.

References

  1. Zollinger, H. Color Chemistry : Syntheses, Properties, and Applications of Organic Dyes and Pigments, 2nd rev. ed.; VCH: Weinheim, 1991. [Google Scholar]
  2. Gordon, P. F.; Gregory, P. Organic Chemistry in Colour; Springer-Verlag: New York, 1983. [Google Scholar]
  3. Abrahart, E.N. Dyes and Their Intermediates, 2nd ed.; Edward Arnold: London, 1977. [Google Scholar]
  4. Ramos, S. S.; Vilhena, A. F.; Santos, L.; Almeida, P. Magn. Reson. Chem. 2000, 38, 475–478.
  5. Ross, J. A.; Ross, B. P.; Rubinsztein-Dunlop, H.; McGeary, R. P. Synth. Commun. 2006, 36, 1745–1750.
  6. The 13C NMR spectra of 3-6 were run at 75 MHz whereas the 13C NMR spectrum of 2 was recorded at 100 MHz to enable resolution of the resonances which appeared at 27.46 and 27.43 ppm in the 100 MHz spectrum.

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MDPI and ACS Style

Ross, J.A.; Ross, B.P.; Cosgrove, K.L.; Rubinsztein-Dunlop, H.; McGeary, R.P. Rhodamine B Pentyl Ester and its Methyl, Ethyl, Propyl, and Butyl Homologues. Molbank 2006, 2006, M515. https://doi.org/10.3390/M515

AMA Style

Ross JA, Ross BP, Cosgrove KL, Rubinsztein-Dunlop H, McGeary RP. Rhodamine B Pentyl Ester and its Methyl, Ethyl, Propyl, and Butyl Homologues. Molbank. 2006; 2006(6):M515. https://doi.org/10.3390/M515

Chicago/Turabian Style

Ross, Justin A., Benjamin P. Ross, Kelly L. Cosgrove, Halina Rubinsztein-Dunlop, and Ross P. McGeary. 2006. "Rhodamine B Pentyl Ester and its Methyl, Ethyl, Propyl, and Butyl Homologues" Molbank 2006, no. 6: M515. https://doi.org/10.3390/M515

APA Style

Ross, J. A., Ross, B. P., Cosgrove, K. L., Rubinsztein-Dunlop, H., & McGeary, R. P. (2006). Rhodamine B Pentyl Ester and its Methyl, Ethyl, Propyl, and Butyl Homologues. Molbank, 2006(6), M515. https://doi.org/10.3390/M515

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