1. of novel 1,2,3-triazolyl appended L-ascorbic acid derivatives
Continuous flow-ultrasonic synergy in click reactions for the synthesis
of novel 1,2,3-triazolyl appended L-ascorbic acid derivatives
Andrijana Meščić,1 Anita Šalić,2 Tomislav Gregorić,1 Bruno Zelić2 and Silvana Raić-Malić1
University of Zagreb, Faculty of Chemical Engineering and Technology: 1Department of Organic Chemistry, Marulićev trg 20, HR Zagreb, Croatia
2Department of Reaction Engineering and Catalysis, Savska cesta 16, HR Zagreb, Croatia.
INTRODUCTION
Flow chemistry technique performs a chemical reaction in a continuously flowing stream in a network of interconnecting tubes. Although click reactions are traditionally conducted in batch process, the progress toward increased sustainability that requires novel approaches with reduced environmental impact opened up in recent years continuous-flow as a novel alternative to conventional batch-based synthesis. Microreactor technology has the potential to revolutionize the pharmaceutical industry because the number of potential drug candidates that can be prepared and screened can be considerably increased, hence the likelihood of developing new drugs is considerably enhanced.[1]
Realizing the benefits of flow chemistry and in continuation of our study towards the synthesis of 1,2,3-triazole-containing heterocycle pharmacophores [2, 3], we report herein the first Cu(I)-catalyzed 1,3-dipolar cycloaddition of azido functionalized L-ascorbic acid derivative and selected alkynes to provide target 1,2,3-triazolyl appended 4,5-didehydro-5,6-dideoxy-L-ascorbic acid library (2a-2n), as molecules with unique biological properties, using innovative ultrasound and continuous flow hybrid system.
SYNTHESES
FLOW CHEMISTRY VS BATCH METHODS
Triazolyl appended 4,5-unsaturated L-ascorbic acid derivatives 2a–2n were obtained through the a reaction of C-6 azido L-ascorbic acid derivative 1 and versetile terminal alkynes (Scheme 1).
In order to investigate the advantages of flow chemistry over batch methods, the Cu(I)-catalyzed click reactions of the azido derivative 1 and alkynes were performed in a microreactor system.
Two enabling technologies, micro-flow chemistry (Figure 1) and ultrasound irradiation have been combined and compared to batch mode synthesis (Table 1).
Table 1. A comparison of continuous micro-flow and batch approaches for the synthesis of 1,2,3-triazolyl appended 4,5-unsaturated L-ascorbic acid library.
Figure 1. The microreactor system used for the synthesis of compd. 2a-2n. The microreactor is directly immersed in the ultrasonic bath.
The yields were dependent on the C-8 substituents at the 1,2,3-triazole scaffold.
The effects of the C-8 substituents in continuous micro-flow and batch syntheses were similar.
The ultrasonic-assisted flow method gave better yields.
Scheme 1. Synthesis of novel 1,4-disubstituted-1,2,3-triazole-L-ascorbic acid derivatives 2a-2n.
ANTITUMORAL ACTIVITIES
Table 2. The growth-inhibition effects in vitro of compounds 2a-2n on selected tumor cell lines and normal fibroblasts.
CONCLUSIONS
New hybrids of L-ascorbic acid and 1,2,3-triazole units were obtained in batch and via synergistic use of microreactor technology and ultrasonic irradiation.
Implementation of ultrasound with flow chemistry:
1. accelerated hour-scale reaction conditions in batch to the minute range in micro-flow device
2. considerably improved the yields.
Comp. 2c and 2e with a p-bromo- and p-pentylphenyl substituents showed the most significant antitumoral activities on all tested cell lines.
LITERATURE
[1] P. Watts and S. J. Haswell, Drug Discov. Today, 8 (2003) 586–593.
[2] S. Raić-Malić and A. Meščić, Curr. Med. Chem. 22 (2015) 1462–1499.
[3] A. Meščić, A. Šalić, T. Gregorić, B. Zelić and S. Raić-Malić, RSC Adv. 7 (2017) 791–800.
Financial support from the Croatian Science Foundation under the project No