Papers by Ricardo Riguera
Current Chemical Biology, Mar 31, 2015
Journal of Natural Products, Sep 17, 2003
Bacterial strains CF-20 (CECT5719) and C-148 (CECT5718), isolated from cultures of larvae of moll... more Bacterial strains CF-20 (CECT5719) and C-148 (CECT5718), isolated from cultures of larvae of molluscs, are shown to produce substances 1-5 with strong antibiotic activity against Vibrio anguillarum (MIC: 0.03-0.07 mug/mL) and identified as the dd-diketopiperazines cyclo(d)-Pro-(d)-Phe (1), cyclo(d)-Pro-(d)-Leu (2), cyclo(d)-Pro-(d)-Val (3), cyclo(d)-Pro-(d)-Ile (4), and cyclo-trans-4-OH-(d)-Pro-(d)-Phe (5). Comparison with other stereoisomers indicates that inhibition of V. anguillarum is associated with the presence of at least one d-amino acid in the diketopiperazine system. This is the first time a series of dd-diketopiperazines has been isolated from a single natural source and their inhibitory activity against V. anguillarum described.
The methodology for the determination of the absolute stereochemistry of chiral compounds by 1 H ... more The methodology for the determination of the absolute stereochemistry of chiral compounds by 1 H and/or 13 C nuclear magnetic resonance (NMR) of their ( R )- and ( S )-arylmethoxyacetic acid derivatives (MPA, MTPA, BPG, 2-NTBA, 9-AMA, and 9-AHA) is presented. It has been applied to secondary and primary alcohols, aldehyde and ketone cyanohydrins, thiols, amines, carboxylic acids, diols, amino alcohols, and triols.
Oxford University Press eBooks, Jul 9, 2015
Nuclear magnetic resonance spectroscopy (NMR spectroscopy) is a research technique that uses the ... more Nuclear magnetic resonance spectroscopy (NMR spectroscopy) is a research technique that uses the magnetic properties of atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained. Proton NMR (1H NMR) is a technique that applies NMR spectroscopy specifically to the hydrogen-1 nuclei within the molecules of a substance, in order to determine the structure of that substance's molecules. The use of 1H NMR for the assignment of absolute configuration of organic compounds is a well-established technique. Recent research describes the technique's application to mono-, bi- and trifunctional compounds. In addition, several new auxiliary reagents, mono- and biderivatization procedures, on-resin methodologies and more recently, the use of 13C NMR, have been introduced to the field. In The Assignment of the Absolute Configuration by NMR Using Chiral Derivatizing Agents: A Practical Guide, eminent Professor of Organic Chemistry Ricardo Riguera organizes this cutting-edge NMR research. Professor Riguera offers a short and usable guide that introduces the reader to the research with a plethora of details and examples. The book briefly explains the theoretical aspects necessary for understanding the methodology, dedicating most of its space to covering the practical aspects of the assignment, with examples and spectra taken from the authors' own experiments. Upper-level undergraduates, graduate students, and chemical researchers will find this guide useful for their studies and practice.
Tetrahedron-asymmetry, Jun 1, 1997
The asymmetric synthesis of the methyl ester of the natural 13-amino acid of Onchidin (2S,3S)-met... more The asymmetric synthesis of the methyl ester of the natural 13-amino acid of Onchidin (2S,3S)-methyl-3-amino-2-methyl-7-octynoate and its enantiomer is described. The preparation of an enantiomerically pure ~-hydroxy acid through an enantioselective aldol condensation reaction and an intramolecular nucleophilic displacement to form a [3-1actam intermediate are the key steps. (~) 1997 Elsevier Science Ltd
Current Chemical Biology, 2019
Polymer Chemistry, 2017
Polyion complex (PIC) micelles incorporating PEG-dendritic copolymers display an unprecedented st... more Polyion complex (PIC) micelles incorporating PEG-dendritic copolymers display an unprecedented stability towards ionic strength that is amplified via hydrophobic interactions. The tridimensional orientation of peripheral hydrophobic linkers between charged groups and the globular/rigid dendritic scaffold maximizes this stabilization compared to PIC micelles from linear polymers. As a result, micelles stable at concentrations higher than 3 M NaCl are obtained, which represents the highest saline concentration attained with PIC micelles. Advantage of this stabilizing dendritic effect has been taken for the design of a robust, pH-sensitive micelle for the controlled intracellular release of the anticancer drug doxorubicin. This micelle displays a slightly higher toxicity, and distinctive mechanisms of cell uptake and intracellular trafficking relative to the free drug. The preparation of mixed PIC micelles by combining differently functionalized PEG-dendritic block copolymers has allowed to fine-tune their stability, paving the way towards the facile modulation of properties like biodegradability, drug loading, or the response to external stimuli.
Journal of Organic Chemistry, Nov 1, 1998
ChemInform, Mar 27, 1990
ChemInform Abstract (two rotamers, rotation barrier ca. 18 kcal/mol).
Organic Letters, Aug 10, 2000
Oxford University Press eBooks, Jul 9, 2015
The nuclear magnetic resonance (NMR) spectra of two enantiomers are identical. Thus, the first st... more The nuclear magnetic resonance (NMR) spectra of two enantiomers are identical. Thus, the first step in using NMR to distinguish between two enantiomers should be to produce different spectra that eventually can be associated with their different stereochemistry (i.e., the assignment of their absolute configuration). Therefore, it is necessary to introduce a chiral reagent in the NMR media. There are two ways to address this problem. One is to use a chiral solvent, or a chiral agent, that combines with each enantiomer of the substrate to produce diastereomeric complexes/associations that lead to different spectra. This is the so-called chiral solvating agent (CSA) approach; it will not be further discussed here [33–34]. The second approach is to use a chiral auxiliary reagent [13–15] (i.e., a chiral derivatizing agent; CDA) that bonds to the substrate by a covalent linkage. Thus, in the most general method, the two enantiomers of the auxiliary CDA react separately with the substrate, giving two diastereomeric derivatives whose spectral differences carry information that can be associated with their stereochemistry. The CDA method that employs arylalcoxyacetic acids as auxiliaries is the most frequently used. It can be applied to a number of monofunctionals [14–15] (secondary alcohols [35–43], primary alcohols [44–46], aldehyde [47] and ketone cyanohydrins [48–49], thiols [50–51], primary amines [52–56], and carboxylic acids [57–58]), difunctional [13] (sec/sec-1,2-diols [59–61], sec/sec-1,2-amino alcohols [62], prim/sec-1,2-diols [63–65], prim/sec-1,2-aminoalcohols, and sec/prim-1,2-aminoalcohols [66–68]), and trifunctional (prim/sec/sec-1,2,3-triols [13, 69–70]) chiral compounds. Its scope and limitations are well established, and its theoretical foundations are well known, making it a reliable tool for configurational assignment. Figure 1.1 shows a summary of the steps to be followed for the assignment of absolute configuration of a chiral compound with just one asymmetric carbon and with substituents that, for simplicity, are assumed to resonate as singlets. Step 1 (Figure 1.1a): A substrate of unknown configuration (?) is separately derivatized with the two enantiomers of a chiral auxiliary reagent, (R)-Aux and (S)-Aux, producing two diastereomeric derivatives.
Chemischer Informationsdienst, Nov 8, 1977
Isoquinoline Alkaloids. Part 2. Preparation of d,l-Glaucine 1.5 Phosphate from d,l-Laudanosoline ... more Isoquinoline Alkaloids. Part 2. Preparation of d,l-Glaucine 1.5 Phosphate from d,l-Laudanosoline Hydrobromide.-A high-yield, commercially viable synthesis of the title alkaloid (V). times. 1.5H3PO4 is described starting from the compound (I). This process is optimized by methylation of the free base (II), precipitating (III) with HBr in high yield after recrystallization to remove the by-product.-(GORALSKI, C. T.; HASHA,
Current Chemical Biology, Nov 14, 2019
Chemischer Informationsdienst, May 21, 1985
Die antimikrobielle Aktivität der Verbindungen (IV) wurde an 16 Mikroorganismen getestet.
ChemInform, Aug 23, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform, Aug 3, 2010
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Papers by Ricardo Riguera