Enantioselective addition of diethylzinc to aldehydes catalyzed by titanium(IV) complexes of N-sulfonylated beta-amino alcohols with four stereogenic centers

An N-sulfonylated beta-amino alcohol (R,S,S,R)-9 with four stereogenic centers is prepared. The titanium complex of 9 is an effective catalyst to induce excellent enantioselectivities for diethylzinc addition to aromatic aldehydes with ee values up to 99%. The feature of doubling the quantity of Ti(O-i-Pr)4 required relative to the catalytic system of the Ti complex of bidentate N-sulfonylated beta-amino alcohols suggests that the two N-sulfonylated beta-amino alcohol moieties in 9 behave as two independent bidentate ligands in the catalytic system. The results obtained using ligand 15 having one N-sulfonylated beta-amino alcohol blocked support the argument of two independent active bidentate moieties in 9.     

Alternative synthetic route to chiral N-substituted camphor-derived beta-amino alcohols

An alternative route from (1R)-(+)-camphor to chiral N-substituted camphor-derived beta-amino alcohol (4b-e) consists of four steps with a total yield of 28%. N-Alkylation of camphor-derived beta-amino alcohol (4a) involves condensation and hydride reduction in one pot without isolation of intermediates. Condensation of 4a with aldehydes or ketones generates a mixture of 1,3-oxazolidines (6) and imino-alcohols (7), which are reduced to 4b-e by NaBH(4).     

Enantioselective addition of diethylzinc to aldehydes catalyzed by optically active C2-symmetrical bis-beta-amino alcohols

The syntheses of new optically active C(2)-symmetrical bis-beta-amino alcohols 1-6 from (S)-2-(1-hydroxy-1,1-diphenylmethyl)-pyrrolidine are described. Especially attention is focused on bridges, which link the two beta-amino alcohol units. These new chiral ligands have been successfully applied in the catalytic enantioselective addition of diethylzinc to aldehydes to give sec-alcohols in good yields with up to 95% enantiomeric excess.     

L-proline-catalyzed enantioselective one-pot cross-Mannich reaction of aldehydes

This protocol describes a procedure for the synthesis of syn-beta-amino alpha-substituted aldehydes, versatile intermediates in synthetic organic chemistry, via asymmetric, direct, one-pot, three-component, cross-Mannich reaction of two different aldehydes. The reaction consists of two steps; one is the formation of imine by the reaction of aldehyde and p-anisidine in the presence of Pro, and the second step is the enantioselective addition reaction of enamine generated from the other aldehyde and Pro with the imine generated in the first step. As the aldehyde easily racemizes, gamma-amino alcohol was isolated and characterized after reduction. The yield and diastereo- and enantioselectivities are generally excellent. It will take approximately 26 h to complete the protocol: 0.5 h to set up the reaction, 20.5 h for the reaction and 5 h for the isolation and purification.     

Synthesis of tetrazole analogs of gamma- and delta-amino acids.

N-benzyloxycarbonyl-protected alpha- or beta-amino alcohols, easily prepared from alpha- and beta-amino acids, were converted into aldehydes and directly reacted with (triphenyl phosphoranylidene) acetonitrile, leading to unsaturated nitriles. Treatment of nitriles with NaN(3) and ZnBr(2) produced unsaturated gamma- and delta-amino tetrazoles, which were deprotected and converted to the corresponding saturated compounds by catalytic hydrogenation. For the case of delta-amino tetrazole, the methylation of the acidic moiety occurred after treatment with CH(2)N(2), leading to the N(1)- and N(2)-methylated constitutional isomers, which were separated by column chromatography and hydrogenated.     

Synthesis and application of chiral beta-amino disulfides as ligands for the enantioselective addition of diethylzinc to aldehydes

A new class of chiral beta-amino disulfides was synthesized from readily available and inexpensive starting materials by a straightforward method and their abilities as ligands were examined in the enantioselective addition of diethylzinc to aldehydes. Enantiomeric excesses of up to 99% have been obtained using 0.5 mol % of the chiral catalysts.     

Copper(I)/TEMPO-catalyzed aerobic oxidation of primary alcohols to aldehydes with ambient air

This protocol describes a practical laboratory-scale method for aerobic oxidation of primary alcohols to aldehydes, using a chemoselective Cu(I)/TEMPO (TEMPO = 2,2,6,6-tetramethyl-1-piperidinyloxyl) catalyst system. The catalyst is prepared in situ from commercially available reagents, and the reactions are performed in a common organic solvent (acetonitrile) with ambient air as the oxidant. Three different reaction conditions and three procedures for the isolation and purification of the aldehyde product are presented. The oxidations of eight different alcohols, described here, include representative examples of each reaction condition and purification method. Reaction times vary from 20 min to 24 h, depending on the alcohol, whereas the purification methods each take about 2 h. The total time necessary for the complete protocol ranges from 3 to 26 h.     

Oxime-based linker libraries as a general approach for the rapid generation and screening of multidentate inhibitors

The described oxime-based library protocol provides detailed procedures for the linkage of aminooxy functionality with aldehyde building blocks that result in the generation of libraries of multidentate inhibitors. Synthesis of inhibitors for protein tyrosine phosphatases (PTPs) and antagonists directed against the human tumor susceptibility gene 101 (TSG101) are shown as examples. Three steps are involved: (i) the design and synthesis of aminooxy platforms; (ii) tethering with aldehydes to form oxime-based linkages with sufficient purity; and (iii) direct in vitro biological evaluation of oxime products without purification. Each coupling reaction is (i) performed in capped microtubes at room temperature (20-23 °C); (ii) diluted for inhibitory evaluation; and (iii) screened with targets in microplates to provide IC(50) or K(d) values. The synthesis of the aminooxy platforms takes 3-5 d; tethering with the aldehydes takes 24 h; and inhibition assay of enzymes and protein-protein interactions takes 30 min and 2 h, respectively.     

Polystyrene-supported N-sulfonylated amino alcohols and their applications to titanium(IV) complexes catalyzed enantioselective diethylzinc additions to aldehydes

Crosslinked polystyrene-supported resins 4, 7a, and 7b containing N-sulfonylated beta-amino alcohol in 98, 20, and 40% loadings are prepared. Asymmetric diethylzinc additions to benzaldehyde employing titanium complexes of 10 mol % resins 4, 7a, or 7b are examined and the best performed 7a/Ti(O-i-Pr)4 catalytic system applies to various aldehydes to afford desired secondary alcohols in excellent enantioselectivities up to 95% ee. The resin 7a is reused five times, giving the product with enantioselectivities >or=86% ee and an 81% ee is obtained when the resin is used the sixth time. The used resin 7a is refreshed with 1 M HCl and the asymmetric reaction employing the regenerated resin 7a gives the product in 88% ee.     

Secondary structure inducing potential of beta-amino acids: torsion angle clustering facilitates comparison and analysis of the conformation during MD trajectories

While numerous examples of beta-peptides--exclusively composed of beta-amino acids--have been investigated during the past decade, there are only few reports on the conformational preference of a single beta-amino acid when incorporated into a cyclopeptide. The conformational bias of beta-amino acids on the secondary structure of cyclopeptides has been investigated by NMR spectroscopy in combination with distance geometry (DG) and molecular dynamics (MD) calculations using experimental constraints. The atomic coordinate RMSD criterion usually employed for clustering of conformations after DG and MD calculations does not necessarily group similar peptide conformations, as there is an insufficient correlation between atomic coordinates and torsion angles. To improve on this shortcoming and to eliminate any arbitrary decisions during this process, a torsion angle clustering procedure has been implemented. For the cyclic pentapeptides cyclo-(-Val-beta-Hala-Phe-Leu-Ile-) 1 and cyclo-(-Ser-Pro-Leu-beta-Hasn-Asp-) 3, the beta-amino acid is found in the central position of an extended gamma-turn (pseudo gamma-turn, Psigamma-turn), while the beta-Hpro residue in the cyclic hexapeptide cyclo-(-Ser-beta-Hpro-Leu-Asn-Ile-Asp-) 5 preferentially occupies position i+1 of a pseudo beta-turn (Psibeta-turn). These results further corroborate the hypothesis of beta-amino acids being reliable inducers of secondary structure in cyclic penta- and hexapeptides. They can be employed in the de novo design of biologically active cyclopeptides in pharmaceutical research, since the three-dimensional presentation of pharmacophoric groups in the side chains can be tailored by incorporation of beta-amino acids in strategic sequential positions.     

Liquid chromatographic direct resolution of beta-amino acids on a doubly tethered chiral stationary phase containing N--H amide linkage based on (+)-(18-crown-6)- 2,3,11,12-tetracarboxylic acid

A doubly tethered chiral stationary phase (CSP) prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to doubly tethered primary aminoalkyl silica gel was used for the resolution of various beta-amino acids. All the beta-amino acids tested were resolved quite well, the separation (alpha) and the resolution factors (RS) being in the ranges 1.34-2.09 and 2.52-7.45, respectively, with a mobile phase of methanol-water (50:50, v/v) containing 10 mM acetic acid. The chiral recognition efficiency of the doubly-tethered CSP was found to be generally superior to that of the corresponding singly-tethered CSP in the resolution of beta-amino acids. The chiral recognition behaviors for the resolution of beta-amino acids on the doubly tethered CSP were examined by varying the type and content of organic and acidic modifiers in the aqueous mobile phase and the column temperature.     

Asymmetric aldol reaction using boron enolates

The protocol for the preparation of boron enolates and their subsequent reaction with aldehydes is described, providing convenient access to beta-hydroxy ketones in good yields and with high stereoselectivities. The reaction consists of three steps: first, the ketone is rapidly converted to the corresponding boron enolate, by exposure to a chlorodialkylborane and tertiary amine base, which is then reacted in situ with the aldehyde. Finally, oxidative workup of the resultant boron aldolate provides aldol adduct. The reaction procedure requires approximately 28 h to complete over a 2-d period, consisting of 5 h to set up the reaction, whereupon the reaction mixture is left at -20 degrees C overnight (16 h), followed by 7 h for workup and purification.     

Beta-amino acid scan of a class I major histocompatibility complex-restricted alloreactive T-cell epitope

An HLA-B27-restricted self-octapeptide known to react with an alloreactive T-cell receptor has been modified by systematic substitution of a beta-amino acid for the natural alpha-amino acid residue, over the whole length of the parent epitope. All modified peptides were shown to bind to recombinant HLA-B*2705 and induce stable major histocompatibility complex-peptide complexes, but with some variation depending on the position of the beta-amino acid on the peptide sequence. Alteration of the natural peptide sequence at the two N-terminal positions (positions 1 and 2) decreases binding affinity and thermodynamic stability of the refolded complex, but all other positions (from position 3 to the C-terminal residue) were insensitive to the beta-amino acid substitution. All modified peptides were recognized by an alloreactive T-cell clone specific for the parent epitope with decreased efficiency, to an extent dependent of the position that was modified. Furthermore, the introduction of a single beta-amino acid at the first two positions of the modified peptide was shown to be sufficient to protect them against enzymatic cleavage. Thus, beta-amino acids represent new interesting templates for alteration of T-cell epitopes to design either synthetic vaccines of T-cell receptor antagonists.     

The twists and turns of beta-peptides.

Recently, it has been discovered that peptides composed of beta-amino acids are capable of adopting novel secondary structures demonstrating that peptides composed of alpha-amino acids are not unique in their ability to fold into well-defined structures. Cyclic as well as acyclic peptides composed of beta-amino acid residues adopt turn, helical, and sheet-like conformations. Here, we discuss the synthesis and conformational preferences of individual, substituted beta-amino acids as well as the structures that peptides composed of these residues, beta-peptides, may adopt.     

A Protocol for the secure linking of registries for HPV surveillance

Introduction

In order to monitor the effectiveness of HPV vaccination in Canada the linkage of multiple data registries may be required. These registries may not always be managed by the same organization and, furthermore, privacy legislation or practices may restrict any data linkages of records that can actually be done among registries. The objective of this study was to develop a secure protocol for linking data from different registries and to allow on-going monitoring of HPV vaccine effectiveness.

Methods

A secure linking protocol, using commutative hash functions and secure multi-party computation techniques was developed. This protocol allows for the exact matching of records among registries and the computation of statistics on the linked data while meeting five practical requirements to ensure patient confidentiality and privacy. The statistics considered were: odds ratio and its confidence interval, chi-square test, and relative risk and its confidence interval. Additional statistics on contingency tables, such as other measures of association, can be added using the same principles presented. The computation time performance of this protocol was evaluated.

Results

The protocol has acceptable computation time and scales linearly with the size of the data set and the size of the contingency table. The worse case computation time for up to 100,000 patients returned by each query and a 16 cell contingency table is less than 4 hours for basic statistics, and the best case is under 3 hours.

Discussion

A computationally practical protocol for the secure linking of data from multiple registries has been demonstrated in the context of HPV vaccine initiative impact assessment. The basic protocol can be generalized to the surveillance of other conditions, diseases, or vaccination programs.     

Peterson olefination from alpha-silyl aldehydes

A procedure for the stereoselective synthesis of substituted alkenes from alpha-silyl aldehydes, via the Peterson reaction, is described. The protocol for the preparation of alpha-silyl aldehydes is also included. Organometallic addition to the alpha-silyl aldehyde gives erythro-beta-hydroxysilanes in high yields (85-90%), which undergo elimination on treatment with potassium hydride (KH) or boron trifluoride to afford respectively Z- o E-alkenes (87-90%). The method described has been carried out using alpha-silyl aldehydes bearing the tert-butyldiphenylsilyl group. This bulky group increases the stability of the silyl aldehyde, enhances the stereoselectivity of the formation of the beta-hydroxysilanes and favors the stereocontrol of the elimination step, thus providing high yields of stereo-defined alkenes. Here we describe a two-step protocol for the synthesis of Z-1-phenyl-1-hexene from 2-tert-butyldiphenylsilyl-2-phenylethanal and n-butyllithium, followed by elimination of the resulting (1S*,2R*)-1-tert-butyldiphenylsilyl-1-phenylhexan-2-ol with KH. The total time for the synthesis, purification and isolation of the alkene is 2 days.     

Aldehyde volatiles emitted in succession from mechanically damaged leaves of poplar cuttings

Plant aldehydes are volatiles necessary to defenses against environmental stress. To explore their emissions in response to wounding, we performed gas chromatography-mass spectrometry (GC-MS) on cuttings from poplar (Populus simonii×P. pyramidalis ‘Opera 8277’) that were mechanically damaged to mimic herbivore attack. We detected 16 aldehydes, including 11 linear saturated aldehydes, 3 linear unsaturated aldehydes, and 2 non-linear aldehydes. Emissions of these aldehydes were clearly enhanced by such treatment, and exhibited a similar pattern of change, i.e., increasing in the first 2 h, then sharply decreasing before rising again at about 12 h. Two release peaks for these aldehydes were observed. Therefore, we propose two pathways for the mediation of aldehyde emissions following damage. The first peak may represent emissions from plant storage pools, whereas the second release peak might result from greater formationde novo through an activated synthesis pathway.     

Synthesis of peptide macrocycles using unprotected amino aldehydes

This protocol describes a method for synthesizing peptide macrocycles from linear peptide precursors, isocyanides and aziridine aldehydes. The effects of the reaction components on the efficiency of the process are discussed. Macrocyclization is exemplified by the preparation of a nine-membered ring peptide macrocycle. The product is further functionalized by nucleophilic opening of the aziridine ring with a fluorescent thiol. This transformation constitutes a useful late-stage functionalization of a macrocyclic peptide molecule. The experimental section describes the selection of the required starting materials, and the preparation of a representative aziridine-2-carboxaldehyde dimer. The synthesis and isolation of the peptide macrocycle can be accomplished in 6 h, and the ring-opening requires approximately 6-8 h. The aziridine-2-carboxaldehyde reagent is commercially available or can be synthesized from readily available starting materials in approximately 4 d. The strategy described is not limited to the specific peptide, isocyanide, aziridine aldehyde or nucleophile used in the representative synthesis.     

From beta-N-tert-butyloxycarbonyl N-carboxyanhydrides to beta-aminoacid derivatives.

beta-N-tert-butyloxycarbonyl-N-carboxyanhydrides are very reactive beta-amino acid derivatives. They react cleanly and smoothly with different nucleophiles like aminoesters, enolates, N-methyl-d-glucamine, amidoximes to afford in good to excellent yields peptides, beta-amino ketocompounds, beta-aminosugars and functionalized disubstituted 1,2,4-oxadiazoles.     

T cell determinants incorporating beta-amino acid residues are protease resistant and remain immunogenic in vivo

A major hurdle in designing successful epitope-based vaccines resides in the delivery, stability, and immunogenicity of the peptide immunogen. The short-lived nature of unmodified peptide-based vaccines in vivo limits their therapeutic application in the immunotherapy of cancers and chronic viral infections as well as their use in generating prophylactic immunity. The incorporation of beta-amino acids into peptides decreases proteolysis, yet its potential application in the rational design of T cell mimotopes is poorly understood. To address this, we have replaced each residue of the SIINFEKL epitope individually with the corresponding beta-amino acid and examined the resultant efficacy of these mimotopes. Some analogs displayed similar MHC binding and superior protease stability compared with the native epitope. Importantly, these analogs were able to generate cross-reactive CTLs in vivo that were capable of lysing tumor cells that expressed the unmodified epitope as a surrogate tumor Ag. Structural analysis of peptides in which anchor residues were substituted with beta-amino acids revealed the basis for enhanced MHC binding and retention of immunogenicity observed for these analogs and paves the way for future vaccine design using beta-amino acids. We conclude that the rational incorporation of beta-amino acids into T cell determinants is a powerful alternative to the traditional homologous substitution of randomly chosen naturally occurring alpha-amino acids, and these mimotopes may prove particularly useful for inclusion in epitope-based vaccines.