In the Laboratory
Microwave-Assisted Hydantoins Synthesis on Solid Support Thibault Coursindel, Jean Martinez, and Isabelle Parrot* D epartement de Chimie, Faculte des Sciences, Universit e Montpellier 2, Place Eug ene Bataillon, 34095 Montpellier Cedex 5, France *
[email protected] This laboratory activity was designed to expose students to the powerful combination of the solid-phase (1-5) and microwave technologies (6). In a teaching laboratory, a library of heterocycles can be synthesized using commercially available preloaded resins with protected amino acids. We propose a simple three-step strategy, involving an original cyclative-cleavage pathway. Hydantoin (glycolylurea or imidazolidine-2,4-dione) (1, Figure 1) is a heterocyclic structure that can be thought of as the product of a cyclic double-condensation reaction involving glycolic acid and urea. Hydantoins (2, Figure 1) are small heterocycle scaffolds involved in several drug structures such as the wellknown anticonvulsant drugs used in epileptic treatment (for example, phenytoin in Figure 1). This moiety is found in many compounds active against a broad range of pharmacological targets (7) with herbicidal, fungicidal, antifungal, antibacterial, antiviral, anti-inflammatory, neuroprotective, analgesic, antiarrhytmic, or antihypertensive properties as well as diuretic activities (8-17). Small variations on either or both R1 and R2 may affect the biological activity of the parent compound. Structure-activity relationship studies are conventional practices in medicinal chemistry and are important in the search of new biologically active compounds. By altering the chemical structure or inserting new chemical groups into the original biomedical compound, medicinal chemists evaluate the modifications for their biological effects. Because hydantoins are valuable pharmacophoric moieties, the desire to prepare libraries for biological tests quickly and efficiently has resulted in the design of various solid-phase approaches. Polymer-supported strategies, in particular, possess a number of obvious advantages; the most important is the ease of workup. By developing a cyclative-cleavage process (9, 18-23) that allows both cyclization and release from the resin in one step, the disadvantage of the supplementary cleavage reaction, usually required in solid-phase strategies, was circumvented (Scheme 1). By adding a microwave component to the solidphase technique, libraries of hydantoins can be prepared with reaction times in minutes instead of hours. Using a microwave oven strictly designed for research laboratory, experiments can be performed with laboratory glassware with good to excellent yields and purities. Experiment Design The experiment was designed for students who have acquired theoretical knowledge in solid-phase synthesis and are 640
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familiar with the properties of the different polymeric supports; the diversity of linkers; the strategies and problems to transpose a synthesis in solution to solid support; the analytical strategies used on solid supports; and the combinatorial chemistry strategies, parallel, split, and mix. The experiment has been tested and is suitable for a one-day organic chemistry laboratory classroom. A simple three-step synthesis of hydantoins was designed starting from commercially available resins preloaded with the first protected amino acid (Scheme 2). In the first step, the protecting group, either 9H-fluoren-9-ylmethoxycarbonyl (Fmoc) or tert-butyloxycarbonyl (Boc), is removed from the amino acid of the preloaded resin (6) at room temperature in 30 min. The completeness of the deprotection is assessed using the Kaiser colorimetric test (24) to confirm the presence of free amines. In the second step, the additive coupling of phenylisocyanate to the resin (7) occurs in 10 min using the microwave oven to afford the linear urea derivative (8). In the third step, the cyclative release step in a triethylamine media in 15 min using the microwave oven produces the desired 3,5-disubstituted hydantoin (9). The purity of the crude hydantoin can be estimated by TLC and HPLC. Structure of the hydantoin can be confirmed by LC-MS, ESI-MS as well as 1H NMR. At each step of the synthesis, IR spectra can be obtained on a KBr pellet to visualize and characterize specific IR bands such as the urea band at 1656 cm-1. Prelab Literature articles about the solid-phase and the microwave technologies with advantages and drawbacks can be handed out by the instructor (25-27). As a prelab or during a tutorial session, the students can read the publication of Park and Kurth that reports the synthesis of hydantoin on two different resins at reflux or room temperature in 22 h (22). Organization The class follows a general procedure and the experiment is conducted over one day. Two teaching strategies can be considered. In the first strategy, the instructor provides the commercially available preloaded resins and gives the structures of the final hydantoins to be obtained. In the second strategy, students are more independent and are asked to choose which substituted hydantoin they would like to synthesize using the commercially available starting materials. In the latter strategy, the students select
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In the Laboratory Table 1. Resins and Reagents Used To Produce the Hydantoins
Figure 1. General formula of hydantoins (1), 3,5-disubstituted hydantoins (2), and examples of hydantoins with biological activity. Scheme 1. General Scheme To Illustrate the Cyclative Cleavage
Scheme 2. Three-Step Hydantoin Synthesisa
a
Note that the phenyl group from the phenylisocyanate acts as the R2 group in Figure 1 and Table 1.
(i) the appropriate polymeric support such as PS, PEG, Tentagel (TGA), and so forth (ii) a preloaded resin connected via a linker to the first protected amino acid, such as a Wang or a Merrifield's linker (iii) the type of amino acid, such as Phe, Gly, Ala, and so forth (iv) a suitable isocyanate derivative, such as phenylisocyanate
In both teaching strategies, the class is divided in two groups: one group works on the influence of the polymer or linker and the other group works on the influence of the preloaded amino
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a Yields are determined by weighing of crude sample (the purity is determined by HPLC analysis) (9). b The connectivity with proline is slightly different than shown in the table. The R1 group is also attached to the N to form the 5-membered proline ring.
acids by comparing the yields of the various hydantoins they have built. Moreover, the small library of hydantoins synthesized
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(Table 1) by all of the students can be compared to demonstrate a combinatorial parallel synthesis (28, 29). The yield is calculated for the three steps based on the initial quantity of the preload resin (9). The experimental process, organization, and the choice of resins can be introduced during a tutorial session. Another tutorial session can be dedicated to sharing results among the students and to make conclusions. Hazards Piperidine, triethylamine, THF, methanol, and pyridine are flammable. Poisoning may occur from ingestion, inhalation, or percutaneous absorption of methanol, piperidine, phenyl isocyanate, dichloromethane, DMF, phenol, THF, potassium cyanide, pyridine, and ninhydrin. Phenyl isocyanate and triethylamine are also lachrymators. Triethylamine and phenol are corrosive and may damage the skin. Potassium cyanide is dangerous to the environment. Students must wear a lab coat, safety glasses, and protective gloves and work in a fume hood. Pedagogical Benefits for Students A simple and short procedure to obtain a library of hydantoins that takes advantage of the solid-phase and the microwave tools is described. In this experiment, several theoretical and experimental notions are developed: (i) introduction to modern technologies such as microwave-assisted synthesis and the concept of solid-phase organic synthesis (SPOS) (30); (ii) selection of a resin according to its application; (iii) introduction to conventional protecting groups employed in amino acid chemistry; (iv) realization of a colorimetric test on solid support or IR to check the completion of a reaction (24); (v) familiarization with analytical techniques such as analytical HPLC, LC-MS, ESI-MS, 1H NMR, and so forth; (vi) interpretation of the results pooled by the class and integration to a parallel strategy; and (vii) elaboration of a plausible mechanism for the cyclative cleavage. Acknowledgment We gratefully acknowledge the support of the IBMM and the Departement d'Enseignement de Chimie de l'Universite Montpellier 2, France. We also wish to thank the students of the Professionnal M.Sc. “Strategies de Decouverte de Molecules Bio-actives” for their active participation while trying this new experimental classroom. Literature Cited 1. Dai, W. M.; Shi, J. Y. Comb. Chem. High Throughput Screening 2007, 10, 837. 2. Gordon, K.; Balasubramanian, S. J. Chem. Technol. Biotechnol. 1999, 74, 835. 3. Jung, N.; Wiehn, M.; Brase, S. In Combinatorial Chemistry on Solid Supports, 2007; Vol. 278, 1. 4. Kirin, S. I.; Noor, F.; Metzler-Nolte, N.; Mier, W. J. Chem. Educ. 2007, 84, 108.
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5. Hailstone, E.; Huther, N.; Parsons, A. F. J. Chem. Educ. 2003, 80, 1444. 6. Musiol, R.; Tyman-Szram, B.; Polanski, J. J. Chem. Educ. 2006, 83, 632. 7. Meusel, M.; Gutschow, M. Org. Prep. Proc. Int. 2004, 36, 391. 8. Brouillette, W. J.; Jestkov, V. P.; Brown, M. L.; Akhtar, M. S.; Delorey, T. M.; Brown, G. B. J. Med. Chem. 1994, 37, 3289. 9. Colacino, E.; Lamaty, F.; Martinez, J.; Parrot, I. Tetrahedron Lett. 2007, 48, 5317. 10. Kuang, R. Z.; Epp, J. B.; Ruan, S.; Chong, L. S.; Venkataraman, R.; Tu, J.; He, S.; Truong, T. M.; Groutas, W. C. Bioorg. Med. Chem. 2000, 8, 1005. 11. Kuang, R. Z.; Epp, J. B.; Ruan, S. M.; Yu, H. Y.; Huang, P.; He, S.; Tu, J.; Schechter, N. M.; Turbov, J.; Froelich, C. J.; Groutas, W. C. J. Am. Chem. Soc. 1999, 121, 8128. 12. Matsugi, T.; Kageyama, M.; Nishimura, K.; Giles, H.; Shirasawa, E. Eur. J. Pharmacol. 1995, 275, 245. 13. Ohta, H.; Jikihara, T.; Wakabayashi, K.; Fujita, T. Pest. Biochem. Physiol. 1980, 14, 153. 14. Osz, E.; Somsak, L.; Szilagyi, L.; Kovacs, L.; Docsa, T.; Toth, B.; Gergely, P. Bioorg. Med. Chem. Lett. 1999, 9, 1385. 15. Schelkun, R. M.; Yuen, P. W.; Serpa, K.; Meltzer, L. T.; Wise, L. D.; Whittemore, E. R.; Woodward, R. M. J. Med. Chem. 2000, 43, 1892. 16. Scicinski, J. J.; Barker, R. D.; Murray, P. J.; Jarvie, E. M. Bioorg. Med. Chem. Lett. 1998, 8, 3609. 17. Stilz, H. U.; Guba, W.; Jablonka, B.; Just, M.; Klingler, O.; Konig, W.; Wehner, V.; Zoller, G. J. Med. Chem. 2001, 44, 1158. 18. Dewitt, S. H.; Kiely, J. S.; Stankovic, C. J.; Schroeder, M. C.; Cody, D. M. R.; Pavia, M. R. Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 6909. 19. Boeijen, A.; Kruijtzer, J. A. W.; Liskamp, R. M. J. Bioorg. Med. Chem. Lett. 1998, 8, 2375. 20. Hanessian, S.; Reinhold, U.; Ninkovic, S. Tetrahedron Lett. 1996, 37, 8967. 21. Kim, S. W.; Ahn, S. Y.; Koh, J. S.; Lee, J. H.; Ro, S.; Cho, H. Y. Tetrahedron Lett. 1997, 38, 4603. 22. Park, K. H.; Kurth, M. J. Tetrahedron Lett. 2000, 41, 740. 23. Stadlwieser, J.; Ellmerer-Muller, E. P.; Tako, A.; Maslouh, N.; Bannwarth, W. Angew. Chem., Int. Ed. 1998, 37, 1402. 24. Kaiser, E.; Colescot., Rl; Bossinge, Cd; Cook, P. I. Anal. Biochem. 1970, 34, 595–598. 25. Kappe, C. O. Angew. Chem., Int. Ed. 2004, 43, 6250. 26. Microwaves in Organic Synthesis; Loupy, A., Ed.; Wiley-VHC: Weinheim, 2002. 27. Biotage Home Page. http://www.biotage.com/ (accessed Mar 2010). 28. Miles, W. H.; Gelato, K. A.; Pompizzi, K. M.; Scarbinsky, A. M.; Albrecht, B. K.; Reynolds, E. R. J. Chem. Educ. 2001, 78, 540. 29. Wolkenberg, S. E.; Su, A. I. J. Chem. Educ. 2001, 78, 784. 30. Scott, P. J. H.; Steel, P. G. Eur. J. Org. Chem. 2006, 2251.
Supporting Information Available Instructions for the students (including experimental procedure); notes to the instructor; reaction mechanisms and liquid chromatography; ESI-MS, 1H NMR, and 13C NMR spectra. This material is available via the Internet at http://pubs.acs.org.
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