Proving and Probing the Presence of the Elusive C-H⋅⋅⋅O Hydrogen Bond in Liquid Solutions at Room Temperature.

Hydrogen bonds (H bonds) play a major role in defining the structure and properties of many substances, as well as phenomena and processes. Traditional H bonds are ubiquitous in nature, yet the demonstration of weak H bonds that occur between a highly polarized C-H group and an electron-rich oxygen atom, has proven elusive. Detailed here are linear and nonlinear IR spectroscopy experiments that reveal the presence of H bonds between the chloroform C-H group and an amide carbonyl oxygen atom in solution at room temperature.

Synthesis of the Aminovinylcysteine-Containing C-Terminal Macrocycle of the Linaridins.

-Phthalimido-d-cysteine allyl ester was -alkylated with 2-iodoethanol. The derived β-thioaldehyde was condensed with α-tetrachlorophthalimidovalinamide to afford a -thioenamide. Removal of the tetrachlorophthalimido protecting group and homologation with -Boc-l-leucine afforded the linear tripeptide.

Total Synthesis of Alloviroidin.

Alloviroidin is a cyclic heptapeptide, produced by several species of Amanita mushrooms, that demonstrates high affinity for F-actin as is characteristic of virotoxins and phallotoxins. Alloviroidin was synthesized via a [3 + 4] fragment condensation of Fmoc-d-Thr(OTBS)-d-Ser(OTBS)-(2 S,3 R,4 R)-DHPro(OTBS)-OH and H-Ala-Trp(2-SOMe)-(2 S,4 S)-DHLeu(5-OTBS)-Val-OMe to form bond A. The linear heptapeptide favored a turn conformation, facilitating cyclization between Val and d-Thr (position B).

Structural modification of the tripeptide KPV by reductive "glycoalkylation" of the lysine residue.

Peptides that exhibit enzymatic or hormonal activities are regulatory factors and desirable therapeutic drugs because of their high target specificity and minimal side effects. Unfortunately, these drugs are susceptible to enzymatic degradation, leading to their rapid elimination and thereby demanding frequent dosage. Structurally modified forms of some peptide drugs have shown enhanced pharmacokinetics, improving their oral bioavailability.

Influence of Sulfur on Acid-Mediated Enamide Formation.

The acid-mediated condensation of acetamide with butanal dimethylacetal and EtSCHCH(OMe), followed by dehydration, was investigated by electronic structure calculations that supported the prediction that the Z-geometry would be favored in the product. The reaction was investigated experimentally using suitably functionalized cysteine building blocks. Some side reactions and optimization of reaction conditions are reported, en route to identifying a mild, inexpensive Lewis acid that achieves a reasonable yield of (Z)-thioenamide 21 with high stereoselectivity.

Crystal Structure of Carboxyltransferase from Staphylococcus aureus Bound to the Antibacterial Agent Moiramide B.

The dramatic increase in the prevalence of antibiotic-resistant bacteria has necessitated a search for new antibacterial agents against novel targets. Moiramide B is a natural product, broad-spectrum antibiotic that inhibits the carboxyltransferase component of acetyl-CoA carboxylase, which catalyzes the first committed step in fatty acid synthesis. Herein, we report the 2.

Design, synthesis, and antibacterial properties of dual-ligand inhibitors of acetyl-CoA carboxylase.

There is an urgent demand for the development of new antibiotics due to the increase in drug-resistant pathogenic bacteria. A novel target is the multifunctional enzyme acetyl-CoA carboxylase (ACC), which catalyzes the first committed step in fatty acid synthesis and consists of two enzymes: biotin carboxylase and carboxyltransferase. Covalently attaching known inhibitors against these enzymes with saturated hydrocarbon linkers of different lengths generated dual-ligand inhibitors.

Conformational changes associated with post-translational modifications of Pro(143) in Skp1 of Dictyostelium--a dipeptide model system.

Prolyl hydroxylation and subsequent glycosylation of the E3(SCF) ubiquitin ligase subunit Skp1 affects its conformation and its interaction with F-box proteins and, ultimately, O2-sensing in the organism. Taking a reductionist approach to understand the molecular basis for these effects, a series of end-capped Thr-Pro dipeptides was synthesized, tracking the sequential post-translational modifications that occur in the protein. The conformation of the pyrrolidine ring in each compound was gauged via coupling constants ((3)JHα,Hβ) and the electronegativity of the Cγ-substituents by chemical shifts ((13)C).

Synthesis of oligomers of β-l-arabinofuranosides of (4R)-4-hydroxy-l-proline relevant to the mugwort pollen allergen, Art v 1.

An efficient, convergent solution phase synthesis of monomer, dimer, trimer and tetramer of the β-l-arabinofuranosylated hydroxyproline (β-l-Araf-Hyp) glycocluster is described. This motif constitutes the carbohydrate-specific epitope of Art v 1, the major allergen of mugwort pollen. While a single monomeric unit was proposed at the outset, poor yields for the seemingly trivial steps of end-capping to replace protecting groups with N-terminal acetamides and C-terminal methyl amides led to the introduction of N-terminal, central and C-terminal β-l-Araf-Hyp building blocks.

Synthesis of orthogonally protected (2S)-2-amino-adipic acid (α-AAA) and (2S,4R)-2-amino-4-hydroxyadipic acid (Ahad).

(2S,4R)-2-amino-4-hydroxyadipic acid (Ahad) building block 45 was synthesized in 11 steps and 6.5% overall yield from commercially available materials. Key steps in stereocontrol were an asymmetric conjugate addition employing a proline-based catalyst and a syn-selective intramolecular-conjugate addition of an oxygen nucleophile to an α,β-unsaturated ester.

Glycosides of hydroxyproline: some recent, unusual discoveries.

Glycosides of hydroxyproline (Hyp) in the plant cell wall matrix were discovered by Lamport and co-workers in the 1960s. Since then, much has been learned about these Hyp-rich glycoproteins. The intent of this review was to compare and contrast some less common structural motifs, in nontraditional roles, to uncover themes.

Evidence that thaxtomin C is a pathogenicity determinant of Streptomyces ipomoeae, the causative agent of Streptomyces soil rot disease of sweet potato.

Streptomyces ipomoeae is the causal agent of Streptomyces soil rot of sweet potato, a disease marked by highly necrotic destruction of adventitious roots, including the development of necrotic lesions on the fleshy storage roots. Streptomyces potato scab pathogens produce a phytotoxin (thaxtomin A) that appears to facilitate their entrance into host plants. S.

Synthesis of histidinoalanine: a comparison of β-lactone and sulfamidate electrophiles.

Previous syntheses of histidinoalanine (HAL) have led to mixtures of regioisomers and/or stereoisomers. For example, opening of N-Cbz-D-serine-β-lactone (6) with Boc-L-His-OMe (5) gave a 2:1 mixture of τ- and π-regioisomers. The sulfamidate 10, derived from N-benzyl-D-serine methyl ester (11), was reacted with Boc-L-His-OMe (5) to give the τ-HAL derivative 17 as a single isomer in 57% yield.

Requirements for Skp1 processing by cytosolic prolyl 4(trans)-hydroxylase and α-N-acetylglucosaminyltransferase enzymes involved in O₂ signaling in dictyostelium.

The social amoeba Dictyostelium expresses a hypoxia inducible factor-α (HIFα) type prolyl 4-hydroxylase (P4H1) and an α-N-acetylglucosaminyltransferase (Gnt1) that sequentially modify proline-143 of Skp1, a subunit of the SCF (Skp1/Cullin/F-box protein) class of E3 ubiquitin ligases. Prior genetic studies have implicated Skp1 and its modification by these enzymes in O(2) regulation of development, suggesting the existence of an ancient O(2)-sensing mechanism related to modification of the transcription factor HIFα by animal prolyl 4-hydroxylases (PHDs). To better understand the role of Skp1 in P4H1-dependent O(2) signaling, biochemical and biophysical studies were conducted to characterize the reaction product and the basis of Skp1 substrate selection by P4H1 and Gnt1.

Synthesis of a dimer of β-(1,4)-L-arabinosyl-(2S,4R)-4-hydroxyproline inspired by Art v 1, the major allergen of mugwort.

Nα-tert-Butoxycarbonyl-L-trans-4-hydroxyproline allyl ester (Boc-Hyp-OAll) was glycosylated with 2,3,5-tri-O-benzyl-L-arabinose p-cresylthioglycoside in 60% yield with 4:1 β:α stereoselectivity. Deprotection of N- and C-terminii independently gave a prolyl amine and prolyl carboxylate respectively that were coupled under standard conditions with 1-[bis-(dimethylamino)methylene]-1H-1,2,3-triazolo-[4,5,b]-pyridininium hexafluorophosphate 3-oxide (N-HATU) to give the dimer 1 in 46% yield. These results represent the first steps toward the production of homogeneous oligomers to determine the minimal epitope of the Art v 1 allergen.

Peptides containing gamma,delta-dihydroxy-L-leucine.

(+/-)-Dehydroleucine was prepared and resolved by porcine kidney acylase. Under the conditions of the Sharpless asymmetric dihydroxylation (SAD), employing AD-mix-alpha, N alpha-carbobenzyloxy-(2S)-4,5-dehydroleucine methyl ester (16) gave rise to a 6.5:1.

Beta-glycosides of hydroxyproline via an umpolung approach.

Reaction of 1,2-O-dibutylstannylene-3,4-6-tri-O-benzyl-beta-D-mannopyranose with Nalpha-fluorenylmethoxycarbonyl-cis-4-trifluoromethanesulfonyloxyproline allyl ester led to formation of a beta-mannoside of trans-4-hydroxyproline. Subsequent manipulation of the C2 hydroxy group gave rise to beta-D-Glc and beta-D-GlcNAc derivatives.

The impact of pyrrolidine hydroxylation on the conformation of proline-containing peptides.

[structure: see text] A series of eight dipeptides of the general formula Ac-Phe-Pro-NHMe was synthesized and the thermodynamics of the cis --> trans isomerization about the central amide bond were studied by NMR. Pro* represents the following prolines: l-proline (Pro), l-trans-4-hydroxyproline (Hyp), l-cis-4-hydroxyproline (hyp), l-cis-4-methoxyproline (hyp[OMe]), l-trans-3-hydroxyproline (3-Hyp), l-cis-3-hydroxyproline (3-hyp), l-2,3-trans-3,4-cis-3,4-dihydroxyproline (DHP), and l-2,3-cis-3,4-trans-3,4-dihydroxyproline (dhp). The conformation of the pyrrolidine ring in each case is discussed in light of previous structural studies, analysis of potential stereoelectronic effects, and NMR data.

Factors affecting conformation in proline-containing peptides.

[reaction: see text] NMR was used to study the thermodynamics of the cis --> trans isomerization for prolyl amide bonds in the compounds shown. The magnitude of K(t/c) for C-terminal esters is greater than for the corresponding amides, signifying stronger backbone stereoelectronic effects in esters. Increasing the steric bulk of the N-terminal residue from Ac- to Ac-Gly- favors the trans conformation.

Design, preparation, and characterization of mixed dimers of inducible nitric oxide synthase oxygenase domains.

A limitation of site-directed mutagenesis of homodimeric proteins is that both subunits will carry the same mutation. We have devised a way to prepare mixed dimers, in which only one chain bears a desired mutation, or each chain can bear a different mutation. Using the inducible nitric oxide oxygenase domain as a model, our strategy focused on the co-expression of two differentially tagged versions of the oxygenase domain, with isolation of the desired mixed dimer in two chromatography steps.

Glucofuranosylation with penta-O-propanoyl-beta-D-glucofuranose.

Readily available, crystalline penta-O-propanoyl-beta-D-glucofuranose is shown to be a suitable glycosylating agent for the acid-catalysed, direct synthesis of O-, S- and N-glucofuranosyl compounds. Beta-linked products are formed with good selectivity. Reaction with cyanotrimethylsilane gave the 1,2-O-(1-cyanopropylidene)acetal rather than the C-glycosyl cyanide.

Toward a general strategy for the synthesis of 3,4-dihydroxyprolines from pentose sugars.

A general strategy is proposed, wherein a pentose sugar gamma-lactone can be converted, via a series of nine reactions, to a 3,4-dihydroxyproline, suitably protected for use in peptide synthesis. Thus, D-ribonolactone (6) has been converted to N-fluorenylmethoxycarbonyl-3,4-di-O-tert-butyldimethylsilyloxy-D-2,3-cis-3,4-cis-proline (7) in 18.9% overall yield.

Synthesis of L-2,3-trans-3,4-cis-Dihydroxyproline Building Blocks for Peptide Synthesis.

L-2,3-trans-3,4-cis-N-Fluorenylmethoxycarbonyl-3,4-dihydroxy-3,4-O-isopropylidineproline (9) has been prepared from D-gulonolactone in nine steps and an overall yield of 22%. Compound 9 has been converted to its allyl ester 13. Compounds 9 and 13 were investigated as building blocks for the incorporation of dihydroxyproline into peptides, with compound 9 serving as a carboxyl component and compound 13 as a precursor to an amino component for peptide coupling reactions.