Dihalogen and Solvent-Free Preparation of syn-Bimane

Abstract

Fluorescent bimanes are low molecular weight and low toxicity molecules with applications ranging from biology to LASER dyes. The widespread use of these molecular probes has presumably been stalled by the hazards involved in their current synthetic preparation which involve handling of dangerous halogens like chlorine (gas) and bromine (liq.). The accessibility achieved by the simple and safe dihalogen and solvent-free methodologies described here open the floodgates to additional future practical applications of bimanes.

Key words

bimane - fluorescent - monobromo-bimane - molecular economy - easy and safe synthesis

• References and Notes

• 1 Kosower EM. Pazhenchevsky B. Hershkowitz E. J. Am. Chem. Soc. 1978; 100: 6516
• 2 Kosower EM. Pazhenchevsky B. J. Am. Chem. Soc. 1980; 102: 4983
• 3 Radkowsky AE. Kosower ED. J. Am. Chem. Soc. 1986; 108: 4527
• 4 Lau CM. Thangaraj K. Kumar G. Ramakrishnan VT. Stevens ED. Boyer JH. Politzer IR. Pavlopoulos TG. Heteroat. Chem. 1990; 1: 195
• 5a Mansoor SE. Farrens DL. Biochemistry 2004; 43: 9426
• 5b Skjold-Jørgensen J. Vind J. Svendsen A. Bjerrum MJ. Eur. J. Lipid Sci. Technol. 2016; 118: 1644
• 6a Sosa-Peinado A. González-Andrade M. Biochemistry 2005; 44: 15083
• 6b Nicholas GM. Kováč P. Bewley CA. J. Am. Chem. Soc. 2002; 124: 3492
• 7a Smirnova I. Kasho V. Sugihara J. Kaback HR. Proc. Natl. Acad. Sci. U.S.A. 2013; 110: 8876
• 7b Chaudhuri A. Venkatesh Y. Behara KK. Singh ND. P. Org. Lett. 2017; 19: 1598
• 8 Lapidot I. Baranes D. Pinhasov A. Gellerman G. Albeck A. Grynszpan F. Shatzmiller SE. Med. Chem. 2016; 12: 48
• 9 Das PJ. Diskin-Posner Y. Firer M. Montag M. Grynszpan F. Dalton Trans. 2016; 45: 17123
• 10 Carpino LA. J. Am. Chem. Soc. 1958; 80: 599
• 11 Canadian Centre for Occupational Health & Safety, https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/chlorine.html.
• 12 De Luca L. Giacomelli G. Nieddu G. Synlett 2005; 223
• 13 Mintz J. Walling C. Org. Synth., Coll. Vol. V 1973; 148
• 14 Synthesis of 3,4-Dimethyl-4-chloro-2-pyrazolin-5-one (2) by Chlorination of 3,4-Dimethyl-2-pyrazolin-5-one (1) Using tert-Butyl Hypochlorite 3,4-Dimethyl-2-pyrazoline-5-one (1, 0.49 g, 4.37 mmol) was dissolved in 8 mL of CCl₄ under a nitrogen atmosphere. The solution was cooled to 0 °C. tert-Butyl hypochlorite (0.49 mL, 4.37 mmol, CAS 507-40-4) was slowly added to the reaction mixture dropwise. The reaction mixture was stirred at rt. After stirring for 8 h, the solvent was removed using under reduced pressure at 40 °C, yielding 0.60 g the product 2 (93% yield). ¹H NMR (CDCl₃, 400 MHz): δ = 1.68 (s, 3 H), 2.12 (s, 3 H) ppm. ¹³C NMR (CDCl₃, 100 MHz): δ = 12.6, 21.7, 60.0, 159.9, 173.8 ppm. ESI-MS: m/z calcd for C₅H₈ClN₂O: 147.0325 [MH⁺]; found: 147.0352.
• 15 Synthesis of 3,4-Dimethyl-4-chloro-2-pyrazolin-5-one (2) by Chlorination of 3,4-Dimethyl-2-pyrazolin-5-one (1) Using N-Chlorosuccinimide 3,4-Dimethyl-2-pyrazoline-5-one (1, 0.5 g, 4.45 mmol) was dissolved in 10 mL of DCM. The solution was cooled to 0 °C. NCS (0.59 g, 4.45 mmol, CAS 128-09-6) was added to the reaction mixture over a period of 30 min. The reaction mixture was stirred at rt. After stirring for 12 h. The solvent was removed using under reduced pressure at 40 °C. The resulting residue was dissolved in CCl₄, and filtered to remove solid succinimide and yielding a filtrate. The solvent was removed from the filtrate yielding 0.52 g the product 2 (80% yield). ¹H NMR (CDCl₃, 400 MHz): δ = 1.68 (s, 3 H), 2.12 (s, 3 H) ppm. ¹³C NMR (CDCl₃, 100 MHz): δ = 12.6, 21.7, 60.0, 159.9, 173.8 ppm.
• 16 Synthesis of 3,4-Dimethyl-4-chloro-2-pyrazolin-5-one (2) by Chlorination of 3,4-Dimethyl-2-pyrazolin-5-one (1) Using 1,3-Dichloro-5,5-dimethylhydantoin 3,4-Dimethyl-2-pyrazoline-5-one (1, 0.5 g, 4.45 mmol) was dissolved in 10 mL of CCl₄. The solution was cooled to 0 °C. 1,3-Dichloro-5,5-dimethylhydantoin (0.44 g, 2.22 mmol, CAS 118-52-5) was slowly added to the reaction mixture over a period of 30 min. The reaction mixture was stirred at rt. After stirring for 12 h, a solid precipitate was observed. The precipitate was removed by filtration. The solvent was removed under reduced pressure at 40 °C, yielding 0.50 g the product 2 (76% yield). ¹H NMR (CDCl₃, 400 MHz): δ = 1.68 (s, 3 H), 2.12 (s, 3 H) ppm. ¹³C NMR (CDCl₃, 100 MHz): δ = 12.6, 21.7, 60.0, 159.8, 173.9 ppm.
• 17 Synthesis of 3,4-Dimethyl-4-chloro-2-pyrazolin-5-one (2) by Chlorination of 3,4-Dimethyl-2-pyrazolin-5-one (1) Using Trichloroisocyanuric Acid 3,4-Dimethyl-2-pyrazoline-5-one (1, 0.5 g, 4.45 mmol) was dissolved in 10 mL of DCM. The solution was cooled to 0 °C. Trichloroisocyanuric acid (0.34 g, 1.48 mmol, CAS 87-90-1) was slowly added to the reaction mixture over a period of 30 min. The reaction mixture was stirred at rt. After stirring for 12 h, a solid precipitate of cyanuric acid was observed. The cyanuric acid precipitate was removed by filtration. The solvent was removed under reduced pressure at 40 °C, yielding 0.54 g the product 2 (82% yield). ¹H NMR (CDCl₃, 400 MHz): δ = 1.68 (s, 3 H), 2.12 (s, 3 H) ppm. ¹³C NMR (CDCl₃, 100 MHz): δ = 12.6, 21.7, 60.0, 159.9, 173.8 ppm.
• 18 Trost BM. Science 1991; 254: 1471
• 19 Solvent-Free Synthesis of 3,4-Dimethyl-4-chloro-2-pyrazolin-5-one (2) by Chlorination of 3,4-Dimethyl-2-pyrazolin-5-one (1) Using Trichloroisocyanuric Acid 3,4-Dimethyl-2-pyrazoline-5-one (1, 0.2 g, 1.78 mmol) was finely ground by mortar and pestle. Trichloroisocyanuric acid (0.14 g, 0.59 mmol, CAS 87-90-1) was added to the fine powder and grinding was continued. The progress of the reaction was monitored by TLC. The reaction reached its completion after 15 min. Then, DCM was added to the reaction mixture. The insoluble cyanuric acid was removed by filtration. The solvent was removed under reduced pressure at 40 °C, yielding 0.18 g 3,4-dimethyl-4-chloro-2-pyrazolin-5-one (2, 69% yield). ¹H NMR (CDCl₃, 400 MHz): δ = 1.68 (s, 3 H), 2,12 (s, 3 H) ppm. ¹³C NMR (CDCl₃, 100 MHz): δ = 12.6, 21.7, 60.0, 159.8, 173.9 ppm. ESI-MS: m/z calcd for C₅H₈ClN₂O: 147.0325 [MH⁺]; found: 147.0352.
• 20 Solvent-Free Synthesis of 9,10-Dioxa-syn-(Me,Me)bimane (3) 3,4-Dimethyl-4-chloro-2-pyrazolin-5-one (0.2 g, 1.36 mmol) was melted and added to a scintillation vial containing K₂CO₃·1.5 H₂O (0.945 mg, 5.71 mmol). The two components were rapidly mixed with a spatula at rt. The progress of the reaction was monitored by TLC. The reaction reached completion after 15 min. DCM was added to the reaction mixture in five portions and the combined organic extract was evaporated under reduced pressure. The reaction mixture was purified by column chromatography eluting with hexane/ethyl acetate (1:3). The desired 9,10-dioxa-syn-(Me,Me)bimane (3) was isolated (0.096 g, 73% yield). ¹H NMR (CDCl₃, 400 MHz): δ = 1.80 (s, 3 H), 2.29 (s, 3 H) ppm. ESI-MS: m/z calcd for C₁₀H₁₃N₂O₂: 193.0977 [MH⁺]; found: 193.0992.
• 21 Kosower NS. Kosower EM. Methods Enzymol. 1987; 143: 76
• 22 Synthesis of Monobromobimane (5) by Bromination of syn-(Me,Me)bimane (3) Using NBS syn-(Me,Me)bimane (3, 0.5 g, 2.6 mmol) was dissolved in 50 mL acetonitrile. The reaction mixture was cooled to 0 °C. Recrystallized NBS (0.46 g, 2.6 mmol, CAS. 128-08-5) was slowly (pinchwise) added to the cooled reaction mixture over a period of 30 min. After the addition of N-bromosuccinimide was complete, the reaction mixture was stirred at rt for 12 h. The solvent was then removed under reduced pressure. The residue was purified using flash chromatography eluted with hexane/ethyl acetate (1:1). The product 5 (0.35 g, 50% yield) was isolated. ¹H NMR (CDCl₃, 400 MHz): δ = 1.84 (s, 3 H), 1.89 (s, 3 H), 2.45 (s, 3 H), 4.32 (s, 2 H) ppm. ¹³C NMR (CDCl₃, 100 MHz): δ = 6.9, 11.5, 17.8, 113.2, 115.4, 144.2, 146.0, 159.8, 160.7 ppm. ESI-MS: m/z calcd for C₁₀H₁₂BrN₂O₂: 271.0082 [MH⁺]; found: 271.0067.
• 23 Neogi I. Das PJ. Grynszpan F. US provisional patent application 62/597,448, filed December 12, 2, 2017