Use of biomimetic diversity-oriented synthesis to discover galanthamine-like molecules with biological properties beyond those of the natural product.

Discover Galanthamine-Like Molecules with Biological Properties beyond Those of the Natural Product Henry E. Pelish,1,2 Nicholas J. Westwood,1,2 Yan Feng,2 Tomas Kirchhausen,2,3 and Matthew D. Shair*,1,2 Department of Chemistry and Chemical Biology HarVard UniVersity, Cambridge Massachusetts 02138 Institute of Chemistry and Cell Biology Department of Cell Biology, and Center for Blood Research HarVard Medical School, Boston, Massachusetts 02115 ReceiVed April 26, 2001 ReVised Manuscript ReceiVed May 31, 2001 Natural products are central to biology and medicine, serving as pharmaceutical leads, drugs,4 and powerful reagents for studying cell biology.5 To date, libraries based upon natural products have been synthesized primarily for the purpose of improving the known biological and pharmacokinetic properties of the parent natural products.6,7 In contrast, we have used diversity-oriented synthesis to construct a library based on a natural product, galanthamine (2, Figure 1), with the goal of discovering molecules that exhibit biological effects beyond those previously associated with the natural product. Although 2 is a potent acetylcholinesterase inhibitor,8 our aim was not to improve this activity. Galanthamine was selected because it offered a range of functionality for diversity-generating reactions, it presented a rigid polycyclic core that might lower the potential entropy penalty associated with protein binding, and it allowed for the use of powerful biomimetic reactions in the synthesis.9 In this communication, we report a biomimetic solid-phase synthesis of 2527 molecules based on the alkaloid natural product galanthamine and the identification of a molecule from the library that perturbs the secretory pathway in mammalian cells10sa process unrelated to the acetylcholinesterase inhibitory activity of 2. Our library synthesis strategy took advantage of efficient biomimetic reactions (3 f 4),11 paralleling the biosynthesis of the natural product (1 f 2).12 Following biomimetic solid-phase synthesis of the core structure 4, four diversity-generating reactions were performed to complete the library synthesis (Figure 1). The library synthesis commenced with attachment of a tyrosine derivative to 500-600μm high capacity (1.43 mmol/g) polystyrene beads through a Si-O bond to generate 5 upon deprotection (Scheme 1).13 Reductive amination14 and protecting-group adjustments produced 7. Exposure of 7 to PhI(OAc)2 afforded 8 which was then converted to 9 via Pd-mediated deprotection and spontaneous cyclization. For the library synthesis, building blocks were selected that reacted in >80% yield and as a group possessed diverse physical characteristics. (Figure 2). The first diversity step was accomplished by coupling the phenol of 9 with five primary alcohols to afford 10 (Scheme 1).16 Treatment of 10 with thiols in the presence of nBuLi afforded 11 as a single diastereomer.17 The nitrogen of 11 was either acylated or alkylated, providing compounds that would be neutral or positively charged, respectively, at physiological pH. The last diversification step involved treatment of 12 with hydrazines and hydroxylamines, generating 13.18 The library was prepared as a single copy (1 bead per library member), arrayed in 384-well plates (1 bead per well), and detached from the solid-support with HF-pyridine (13 f 14). Following completion of the synthesis, the presence of 2527 out of 2946 (86%) potential compounds was confirmed by mass spectrometry.19 Evaporation of the cleavage reaction solution and resuspension in 7 μL of DMSO afforded 2527 stock solutions for biological screening. * Towhomcorrespondenceshouldbeaddressed.Email: [email protected]. (1) Department of Chemistry and Chemical Biology, Harvard University. (2) Institute of Chemistry and Cell Biology (ICCB), Harvard Medical School. (3) Department of Cell Biology, and Center for Blood Research, Harvard Medical School. (4) Newman, D. J.; Cragg, G. M.; Snader, K. M. Nat. Prod. Rep. 2000, 17, 215-234. (5) Schreiber, S. L. Chem. Eng. News 1992 (October 26), 22-32. (6) Hall, D. G.; Manku, S.; Wang, F. J. Comb. Chem. 2001, 3(2), 125150. (7) (a) Nicolaou, K. C.; Vourloumis, D.; Li, T.; Pastor, J.; Winssinger, N.; He, Y.; Ninkovis, S.; Sarabia, F.; Vallberg, H.; Roschanger, F.; King, N. P.; Finlay, R. V.; Giannakakou, P.; Verdier-Pinard, P.; Hamel, E. Angew. Chem., Int. Ed. Engl. 1997, 36, 2097-2103. (b) Nicolaou, K. C.; Winssinger, D.; Vourloumis, D.; Ohshima, T.; Kim, S.; Pfefferkorn, J.; Xu, J.-Y.; Li, T. J. Am. Chem. Soc. 1998, 120, 10814-10826. (c) Lee, K. J.; Angulo, A.; Ghazal, P.; Janda, K. D. Org. Lett. 1999, 1, 1859-1862. (d) Xu, R.; Greiveldinger, G.; Marenus, L. E.; Cooper, A.; Ellman, J. A. J. Am. Chem. Soc. 1999, 121, 4898-4899. (e) Wipf, P.; Reeves, J. T.; Balachandran, R.; Giuliano, K. A.; Hamel, E.; Day, B. W. J. Am. Chem. Soc. 2000, 122, 9391-9395. (f) Boger, D. L.; Fink, B. E.; Hedrick, M. P. J. Am. Chem. Soc. 2000, 122, 6382-6394. (g) Nicolaou, K. C.; Pfefferkorn, J. A.; Barluenga, S.; Mitchell, H. J.; Roecker, A. J.; Cao, G.-Q. J. Am. Chem. Soc. 2000, 122, 9968-9976 and references therein. (8) Coyle, J.; Kershaw, P. Biol. Psychiatry 2001, 49(3), 289-299. (9) Lindsley, C. W.; Chan, L. K.; Goess, B. C.; Joseph, R.; Shair, M. D. J. Am. Chem. Soc. 2000, 122, 422-423. (10) Lippincott-Schwartz, J.; Roberts, T. H.; Hirschberg, K. Annu. ReV. Cell DeV. Biol. 2000, 16 557-589. (11) Biomimetic syntheses of galanthamine: (a) Barton, D. H. R.; Kirby, G. W. J. Chem. Soc. 1962, 806-817. (b) Shimizu, K.; Tomioka, K.; Yamada, S.; Koga, K. Chem. Pharm. Bull. 1978, 26, 3765-3771. (c) Kita, Y.; Arisawa, M.; Gyoten, M.; Nakajima, M.; Hamada, R.; Tohma, H.; Takada, T. J. Org. Chem. 1998, 63, 6625-6633. (12) Barton, D. H. R.; Cohen, T. Festschrift A. Stoll; Birkhauser: Basel, 1957. (13) Tallarico, J. A.; Depew, K. M.; Pelish, H. E.; Westwood, N. J.; Lindsley, C. W.; Shair, M. D.; Schreiber, S. L.; Foley, M. A. J. Comb. Chem., 2001, 3, 312-318. (14) Look, G. C.; Murphy, M. M.; Campbell, D. A.; Gallop, M. A. Tetrahedron Lett. 1995, 36, 2937-2940. (15) For the use of hypervalent iodine(III) reagents in similar oxidations, see Krihna, K. V. R.; Sujatha, K.; Kapil, R. S. Tetrahedron Lett. 1990, 31, 1351-1352. Kita, Y.; Takada, T.; Gyoten, M.; Tohma, H.; Zenk, M. H.; Eichhorn, J. J. Org. Chem. 1996, 61, 5857-5864 and references therein. (16) “Skip codon” (Figure 2) refers to the absence of a building block which renders the core structure functionality a diversity element. (17) Observed by NMR and correlated with molecular modeling. See Supporting Information. (18) All combinations of 11 were synthesized in parallel for quality control. Following a pool step, R3 and R4 building blocks were incorporated in parallel to generate 13. See Supporting Information. Figure 1. Biomimetic diversity-oriented synthesis parallels the biosynthesis of galanthamine. 6740 J. Am. Chem. Soc. 2001, 123, 6740-6741