Ignacio Alfonso

Asymmetric Organic Synthesis with Enzymes

METHODOLOGY Medium Engineering: Directed evolution: The search for new enzymes: SYNTHETIC APPLICATIONS Dynamic Kinetic Resolutions: Deracemization and Enantioconvergent Processes: Transesterification and hydrolysis of carboxylic acid derivatives, alcohols and epoxides Aminolysis and ammonolysis of carboxylic acid derivatives: Reduction Reactions: Oxidation Reactions: Making and breaking C-C bonds:

Update 1 of: Enantioselective Enzymatic Desymmetrizations in Organic Synthesis

Update 1 of: Enantioselective Enzymatic Desymmetrizations in Organic Synthesis Eduardo García-Urdiales, Ignacio Alfonso, and Vicente Gotor* Departamento de Química Org anica e Inorg anica, Facultad de Química, Universidad de Oviedo, Juli an Clavería, 8, 33006 Oviedo, Spain, and Departamento de Química Biol ogica y Modelizaci on Molecular, Instituto de Química Avanzada de Catalu~na (IQAC, CSIC), Jordi Girona, 18-26, 08034, Barcelona, Spain This is a Chemical Reviews Perennial Review. The root paper of this title was published in Chem. Rev. 2005, 105 (1), 313 354, DOI: 10.1021/cr040640a; Published (Web) December 17, 2004. Updates to this text appear in red type.

Supramolecular Control for the Modular Synthesis of Pseudopeptidic Macrocycles through an Anion-Templated Reaction

The anion-templated synthesis of different pseudopeptidic macrocycles has been studied in detail by using a multidisciplinary approach. The reaction between an open-chain pseudopeptidic diamine and the appropriate dialdehyde is highly affected by the presence of the best fitting anionic template. The formation of the corresponding macrocyclic tetraimino-template supramolecular complex is demonstrated by NMR (ROESY and PGSE) and mass spectrometry (ESI-TOF). These supramolecular complexes can be easily reduced to the corresponding more stable tetraamine macrocycles. Accordingly, we have used this reaction to efficiently synthesize a family of new pseudopeptidic macrocycles in a one-pot two-steps anion-templated reductive amination reaction, which comprises a multicomponent macrocyclization through the selective formation of four chemical bonds to yield a unique macrocyclic structure. Different variables like the aliphatic spacer between amino acidic moieties, geometry of the dialdehyde, and structure of the amino acid side chains were thoroughly studied, and their effect in the formation and stability of the supramolecular complexes discussed. The conformational preorganization induced by the template has been monitored by circular dichroism, reflecting the differences observed in the isolated yields, as well as by NMR spectroscopy. This effect has been also supported by molecular modeling. All the experimental and theoretical techniques were strongly consistent and reflected the same trends by comparing the different structural variables introduced in the system.

Biocatalytic and biomimetic aminolysis reactions: useful tools for selective transformations on polyfunctional substrates

Aminolysis is a deeply studied reaction, but the development of new catalysts for this process is still an emerging area of organic and bioorganic chemistry. Two different approaches are reviewed in this article: the biomimetic de novo designed synthetic catalysts and the use of natural enzymes. Brief mechanistic considerations are discussed. Some important aspects like chemo-, regio- and stereoselectivity towards the substrates are highlighted on selected examples with synthetic applications.

A Ferromagnetic [Cu3(OH)2]4+ Cluster Formed inside a Tritopic Nonaazapyridinophane: Crystal Structure and Solution Studies†

Chemists working in coordination and/or supramolecular chemistry find a continuous source of inspiration in biomolecules and enzyme active sites. In this respect, trinuclear Cu centers have attracted a lot of interest due to their resemblance to multicenter blue copper oxidases like ascorbate oxidase, ceruloplasmin, lacase oxidase, and particulate methane monooxygenase. These enzymes contain at least four copper centers, which are necessary for four-electron reduction of molecular oxygen to water. For instance, the high-resolution structure of ascorbate oxidase shows that the mononuclear electron-transfer copper site of type 1 (T1) is connected to the trinuclear site through a patch formed by a cysteine residue from which two histidine residues diverge to bind the T3 copper ions. In the oxidized form of the enzyme, the T3 Cu atoms, apart from the imidazole moiety of the histidine residues of the patch, are coordinated by another two imidazole units and by an OH group that bridges the two atoms, which are 3.71 far apart from each other. The geometry around each metal ion can be best described as a trigonal bipyramid with a vacant equatorial position oriented towards the T2 copper atom, which completes the trinuclear center. In the T2 site the Cu center is coordinated in a very particular T-shaped geometry by two histidine residues and a monodentate hydroxo group or a water molecule. The mechanism by which these centers catalyze the fourelectron reduction of molecular dioxygen to water and the magnetic properties of these particular arrangements of copper ions have attracted great interest from both the biochemical and magnetochemical points of view. Therefore, small-molecule studies aimed at mimicking their properties are of great relevance in this respect.

From salts to ionic liquids by systematic structural modifications: a rational approach towards the efficient modular synthesis of enantiopure imidazolium salts.

This paper reports a simple and robust modular synthetic strategy that leads to a large variety of configurationally and structurally diverse imidazole-based chiral ionic liquids (CILs) by lipase-catalyzed resolution. The intimate microscopic interactions of the supramolecular ionic network of these imidazolium chiral salts at the molecular level are investigated both spectroscopically (NMR, FT-IR-ATR) and theoretically, and a topological analysis of the experimental electron densities obtained by X-ray diffraction of single crystals is performed. Our results support the key role played by the relative configuration of the -OR group on the hydrogen-bonding pattern and its strong influence on the final physical properties of the imidazolium salt. We also obtained a reasonable correlation between the observed melting point and the non-covalent interactions. The spectroscopic data and the topological analysis reflect the key role played by hydrogen bonds between the OH and imidazolium C2H groups in both cation-anion and cation-cation interactions, with the presence of an OH group leading to an additional inter-cation interaction. This interaction significantly affects the properties of stereoisomeric salts. Even more interestingly, we also studied the effect of the chirality by comparing enantiopure CILs with their racemic mixtures and found that, with the exception of trans-Cy6-OH-Im-Bn-Br, the melting points of the racemic mixtures are higher than those of the corresponding enantiomerically pure forms. For stereoisomeric examples, we have successfully explained the differences in melting temperatures in light of the corresponding structural data. Chirality should therefore be taken into account as a highly attractive design vector in the preparation of ILs with specifically desired properties.

Optically active dioxatetraazamacrocycles: chemoenzymatic syntheses and applications in chiral anion recognition

Two new C2 and D2 symmetrical dioxatetraaza 18-membered macrocycles [(R,R)-1 and (S,S,S,S)-2] are efficiently synthesized in enantiomerically pure forms by a chemoenzymatic method starting from (+/-)-trans-cyclohexane-1,2-diamine. The protonation constants and the binding constants with different chiral dicarboxylates are determined in aqueous solution by means of pH-metric titrations. The triprotonated form of (S,S,S,S)-2 shows moderate enantioselectivity with malate and tartrate anions (deltadeltaG=0.62 and 0.66 kcal mol(-1), respectively), being the strongest binding observed in both cases with the L enantiomer. Good enantiomeric discrimination is obtained with tetraprotonated (R,R)-1 and N-acetyl aspartate, the complex with the D-enantiomer being 0.92 kcalmol(-1) more stable than its diastereomeric counterpart. Despite the lack of enantioselectivity of tri- and tetraprotonated (R,R)-1 for the tartrate anion, a very good diastereopreference for meso-tartrate is found. All these experimental results allow us to propose a model for the host-guest structure based on coulombic interactions and hydrogen bonds.

Biological activity of synthetic ionophores: ion transporters as prospective drugs?

The control of ion transport and homeostasis is a critical function of living organisms. In this perspective, an overview of different synthetic systems capable of facilitating the transmembrane transport of ions along with the biological activity exerted by these compounds is presented. Examples of both cation selective and anion selective transporters are highlighted. The potential future applications of these systems in the treatment of conditions derived from the dysregulation of natural ion transport mechanisms and the development of new antimicrobials and anticancer drugs are discussed.

Sequential biocatalytic resolution of (±)-trans-cyclohexane-1,2-diamine. Chemoenzymatic synthesis of an optically active polyamine

Candida antarctica lipase-catalysed double monoaminolysis of dimethyl malonate by (±)-trans-cyclohexane-1,2-diamine allows the sequential resolution of the latter compound, affording an enantiopure bis(amidoester), (R,R)-3, which is subsequently transformed into an optically active polyamine, (R,R)-9.

Polyhydroxylated Bicyclic Isoureas and Guanidines Are Potent Glucocerebrosidase Inhibitors and Nanomolar Enzyme Activity Enhancers in Gaucher Cells

Four diastereomeric series of N-alkylated [6+5] bicyclic isoureas having hydroxyl substituents mimicking glucose hydroxyl groups have been synthesized as potential β-glucocerebrosidase (GCase) inhibitors with the aim of developing pharmacological chaperones for enzyme deficiency in Gaucher disease (GD). The bicyclic compounds differ either by the configuration of the ring fusion carbon atoms or by the nature of the N-alkyl substituents. When assayed for effects on GCase activity, the isoureas displayed selective inhibition of GCase with low micromolar to nanomolar IC(50)s in isolated enzyme experiments. One of the series of isoureas, a family having a specific cis ring fusion, exhibited strong inhibition of recombinant GCase activity with K(i) values in the 2-42 nM range. In addition, the [6+5] bicyclic guanidine derivatives with a substitution pattern analogous to the most active isoureas were also found to be potent inhibitors of GCase with K(i) values between 3 and 10 nM. Interestingly, the active bicyclic isoureas and guanidines also behaved as GCase inhibitors in wild-type human fibroblasts at nanomolar concentrations. The potential of these compounds as pharmaceutical chaperones was determined by analyzing their capacity for increasing GCase activity in GD lymphoblasts derived from N370S and L444P variants, two of the most prevalent Gaucher mutations. Six compounds were selected from the different bicyclic isoureas and guanidines obtained that increased GCase activity by 40-110% in N370S and 10-50% in L444P cells at low micromolar to nanomolar concentrations following a 3 day incubation. These results describe a promising series of potent GCase ligands having the cellular properties required for pharmacological chaperones.