molecules Article Synthesis and Evaluation of Novel Iminosugars Prepared from Natural Amino Acids Alejandro Puet 1, Gema Domínguez 1, Francisco Javier Cañada 2,3 and Javier Pérez-Castells 1,* 1 Department of Chemistry and Biochemistry, Facultad de Farmacia, Universidad San Pablo-CEU, CEU Universities, Urbanización Montepríncipe, Boadilla del Monte, 28660 Madrid, Spain; [email protected] (A.P.); [email protected] (G.D.) 2 Centro de Investigaciones Biológicas Margarita Salas, CSIC, Ramiro de Maetzu 9, 28040 Madrid, Spain; [email protected] 3 CIBER de Enfermedades Respiratorias (CIBERES) Avda, Monforte de Lemos 3-5, 28029 Madrid, Spain * Correspondence: [email protected]; Tel.: +34-913724700 Abstract: Cyclopropanated iminosugars have a locked conformation that may enhance the inhibitory activity and selectivity against different glycosidases. We show the synthesis of new cyclopropane- containing piperidines bearing five stereogenic centers from natural amino acids L-serine and L- alanine. Those prepared from the latter amino acid may mimic L-fucose, a natural-occurring monosac- charide involved in many molecular recognition events. Final compounds prepared from L-serine bear S configurations on the C5 position. The synthesis involved a stereoselective cyclopropanation reaction of an α,β-unsaturated piperidone, which was prepared through a ring-closing metathe- sis. The final compounds were tested as possible inhibitors of different glycosidases. The results, although, in general, with low inhibition activity, showed selectivity, depending on the compound and enzyme, and in some cases, an unexpected activity enhancement was observed. Keywords: piperidine iminosugars; glycosidase inhibition; metathesis; sulfur ylide cyclopropanation Citation: Puet, A.; Domínguez, G.; Cañada, F.J.; Pérez-Castells, J. Synthesis and Evaluation of Novel Iminosugars Prepared from Natural 1. Introduction Amino Acids. Molecules 2021, 26, 394. Natural or synthetic polyhydroxylated piperidines are iminosugars able to act as https://doi.org/10.3390/molecules biomimetics of their corresponding pyranose analogs. For instance, nojirimycin, its epimers, 26020394 and their deoxyanalogs have been used as lead molecules to design glycosidase and glycosyl transferase inhibitors and modulators [1–3]. Some iminosugars such as miglitol Academic Editor: Narciso M. Garrido (Glyset®)[4], migalastat (Galafold®)[5], and miglustat (Zavesca®)[6] are commercially Received: 16 December 2020 available, and others are actually in different clinical phases (Figure1). The interaction Accepted: 10 January 2021 with glycosidases is generally attributed to a structural similarity to diverse conformational Published: 13 January 2021 oxocarbenium transition states formed during the hydrolysis of carbohydrates [7]. There are important variations in these transition states for different glycosidases [8,9]. Thus, Publisher’s Note: MDPI stays neu- there is a great interest in designing conformationally restricted inhibitors in order to tral with regard to jurisdictional clai- ms in published maps and institutio- achieve selective inhibition and adequate metabolic stability. nal affiliations. Our group engaged in the synthesis of novel piperidine iminosugars fused to a cyclo- propane ring, resulting in structures with a locked conformation [10,11]. The cyclopropane renders a twist-like conformation to the piperidine ring that is found, as preferred for interactions with certain glycosidases [12,13]. We expect these compounds to be starting Copyright: © 2021 by the authors. Li- points for the finding of products of pharmacological interest (Figure2). The possibility of censee MDPI, Basel, Switzerland. variations in the substitution pattern of the cyclopropane allows different configurations This article is an open access article that could direct their selectivity to different glycosidases. Although the development distributed under the terms and con- of synthetic routes to iminosugars has received much attention in the synthetic commu- ditions of the Creative Commons At- nity [14,15], the preferred chiral pools are carbohydrates, which are transformed using tribution (CC BY) license (https:// reductive aminations [16,17], or other transformation strategies [18]. In our case, we devel- creativecommons.org/licenses/by/ oped synthetic approaches from natural amino acids, which have less precedents [19,20]. 4.0/). Molecules 2021, 26, 394. https://doi.org/10.3390/molecules26020394 https://www.mdpi.com/journal/molecules Article Synthesis and Evaluation of Novel Iminosugars Prepared from Natural Amino Acids Alejandro Puet 1, Gema Domínguez 1, Francisco Javier Cañada 2,3 and Javier Pérez-Castells 1,* 1 Department of Chemistry and Biochemistry, Facultad de Farmacia, Universidad San Pablo-CEU, CEU Universities, Urbanización Montepríncipe, 28660 Boadilla del Monte, Madrid, Spain; [email protected] (A.P.); [email protected] (G.D.) 2 Centro de Investigaciones Biológicas Margarita Salas, CSIC, Ramiro de Maetzu 9, 28040 Madrid, Spain; [email protected] 3 CIBER de Enfermedades Respiratorias (CIBERES) Avda, Monforte de Lemos 3-5, 28029 Madrid, Spain * Correspondence: [email protected]; Tel.: +34-913724700 Abstract: Cyclopropanated iminosugars have a locked conformation that may enhance the inhibi- tory activity and selectivity against different glycosidases. We show the synthesis of new cyclopro- pane-containing piperidines bearing five stereogenic centers from natural amino acids L-serine and L-alanine. Those prepared from the latter amino acid may mimic L-fucose, a natural-occurring mon- osaccharide involved in many molecular recognition events. Final compounds prepared from L- serine bear S configurations on the C5 position. The synthesis involved a stereoselective cyclopro- panation reaction of an α,β-unsaturated piperidone, which was prepared through a ring-closing metathesis. The final compounds were tested as possible inhibitors of different glycosidases. The results, although, in general, with low inhibition activity, showed selectivity, depending on the com- pound and enzyme, and in some cases, an unexpected activity enhancement was observed. Keywords: piperidine iminosugars; glycosidase inhibition; metathesis; sulfur ylide cyclopropana- Citation: Puet, A.; Domínguez, G.; tion Cañada, F.J.; Pérez-Castells, J. Synthesis and evaluation of novel iminosugars prepared from natural amino acids. Molecules 2021, 26, x. 1. Introduction https://doi.org/10.3390/xxxxx Natural or synthetic polyhydroxylated piperidines are iminosugars able to act as bi- omimetics of their corresponding pyranose analogs. For instance, nojirimycin, its epimers, MoleculesAcademic 2021 Editor:, 26 Narciso, x M. Ga- 2 of 19 rrido and their deoxyanalogs have been used as lead molecules to design glycosidase and gly- MoleculesReceived:2021 16 December, 26, 394 2020 cosyl transferase inhibitors and modulators [1–3]. Some iminosugars such as miglitol2 of 19 Accepted: 10 January 2021 (Glyset®) [4], migalastat (Galafold®) [5], and miglustat (Zavesca®) [6] are commercially Published: 13 January 2021 available,Our groupand others engaged are actually in the synthesisin different of clinicalnovel piperidine phases (Figure iminosugars 1). The interaction fused to a cy- withclopropane glycosidases ring, resultingis generally in stattributedructures withto a structurala locked conformationsimilarity to diverse [10,11]. conforma- The cyclopro- Publisher’s Note: MDPI stays neu- Othertionalpane renders asymmetricoxocarbenium a twist-like or transition biocatalyzed conformation states approaches formed to the during havepiperidine the been hydrolysis used ring [21that of]. Incarbohydratesis ourfound, previous as preferred [7]. work, tral with regard to jurisdictional startingTherefor interactions are from important natural with variations certain amino glycosidases acid in these L-serine, transi [12,13].tion we synthesizedstates We expect for different these iminosugars compounds glycosidases bearing to [8,9]. be the start- R claims in published maps and insti- configurationThus,ing points there for is a onthe great thefinding interest carbon of inproducts adjacent designing of to pharmacologicalco nitrogen,nformationally which restrictedinterest was supposed (Figure inhibitors to2). mimic Thein order possibil- C5 in tutional affiliations. naturaltoity achieve of variations carbohydrates selective in inhibitionthe and substitution iminosugars. and adequate pattern metabolic of the cyclopropane stability. allows different configu- rations that could direct their selectivity to different glycosidases. Although the develop- HO Copyright: © 2021 by the authors. ment ofOH synthetic routes to iminosugars has received much attention in the synthetic com- Licensee MDPI, Basel, Switzerland. munityHO [14,15], the preferredHO chiral poolsOH arHOe carbohydrates, whichHO are transformed using NH N NH N This article is an open access article reductive aminations [16,17], or other transformation strategies [18]. In our case, we de- OH OH OH distributed under the terms and con- velopedHO synthetic approachesHO from naturalHO amino acids, whichHO have less precedents ditions of the Creative Commons At- [19,20].OH Other asymmetric orOH biocatalyzed approachesOH have been used [21].OH In our previous tribution (CC BY) license (http://cre- work, startingI from naturalII amino acid L-serine, weIII synthesized iminosugars IV bearing the ativecommons.org/licenses/by/4.0/). FigureFigureR configuration 1. Structures on of of nojirimycinthe nojirimycin carbon ( I