A structure-based design of a new generation of tumor-associated glycopeptides with improved affinity against two anti-MUC1 antibodies is described. These unique antigens feature a fluorinated ...proline residue, such as a (4S)-4-fluoro-l-proline or 4,4-difluoro-l-proline, at the most immunogenic domain. Binding assays using biolayer interferometry reveal 3-fold to 10-fold affinity improvement with respect to the natural (glyco)peptides. According to X-ray crystallography and MD simulations, the fluorinated residues stabilize the antigen–antibody complex by enhancing key CH/π interactions. Interestingly, a notable improvement in detection of cancer-associated anti-MUC1 antibodies from serum of patients with prostate cancer is achieved with the non-natural antigens, which proves that these derivatives can be considered better diagnostic tools than the natural antigen for prostate cancer.
Starting from commercially available (S)-isoserine and effectively accessible (S)-α-methylserine, enantiopure cyclic sulfamidates have been prepared as chiral building blocks for the synthesis of ...various S- and O-glycosylated amino acid derivatives, including unnatural variants of the Tn antigen, through highly chemo-, regio-, and stereoselective nucleophilic ring-opening reactions with carbohydrate C1-S- and C1-O-nucleophiles.
We synthesized and carried out the conformational analysis of several hybrid dipeptides consisting of an α-amino acid attached to a quaternary glyco-β-amino acid. In particular, we combined a ...S-glycosylated β(2,2)-amino acid and two different types of α-amino acid, namely, aliphatic (alanine) and aromatic (phenylalanine and tryptophan) in the sequence of hybrid α/β-dipeptides. The key step in the synthesis involved the ring-opening reaction of a chiral cyclic sulfamidate, inserted in the peptidic sequence, with a sulfur-containing nucleophile by using 1-thio-β-D-glucopyranose derivatives. This reaction of glycosylation occurred with inversion of configuration at the quaternary center. The conformational behavior in aqueous solution of the peptide backbone and the glycosidic linkage for all synthesized hybrid glycopeptides was analyzed by using a protocol that combined NMR experiments and molecular dynamics with time-averaged restraints (MD-tar). Interestingly, the presence of the sulfur heteroatom at the quaternary center of the β-amino acid induced θ torsional angles close to 180° (anti). Notably, this value changed to 60° (gauche) when the peptidic sequence displayed aromatic α-amino acids due to the presence of CH-π interactions between the phenyl or indole ring and the methyl groups of the β-amino acid unit.
A second generation of chiral bicyclic dehydroalanines easily accessible from serine has been developed. These scaffolds behaved as excellent S-Michael acceptors when ...tri-O-acetyl-2-acetamido-2-deoxy-1-thio-α-d-galactopyranose (abbreviated as GalNAc-α-SH) was used as a nucleophile. This addition proceeds with total chemo- and stereoselectivity, complete atom economy, quickly, and at room temperature, making it a true click reaction. The Michael adducts were easily transformed into S-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-l- and -d-cysteines, which can be regarded as mimics of the Tn antigen derived from l-Ser (α-d-GalNAc-l-Ser) and d-Ser (α-d-GalNAc-d-Ser), respectively.
This report describes the gram scale synthesis of (
S)- and (
R)-2,2,4-trimethyl-4-(hydroxymethyl)-1,3-dioxolanes using the Sharpless asymmetric dihydroxylation (AD) of the Weinreb amide of ...2-methyl-2-propenoic acid. The 2-methylglycerol acetonides resultant from protection of the AD products were used as starting materials in the synthesis of
O-benzyl ethers of the valuable C4-chiral building blocks (
S)- and (
R)-2-methylglycidol.
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Stereoselective sulfa-Michael addition of appropriately protected thiocarbohydrates to chiral dehydroalanines has been developed as a key step in the synthesis of biologically important cysteine ...derivatives, such as S-(β-d-glucopyranosyl)-d-cysteine, which has not been synthesized to date, and S-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-l-cysteine, which could be considered as a mimic of Tn antigen. The corresponding diamide derivative was also synthesized and analyzed from a conformational viewpoint, and its bound state with a lectin was studied.
The first examples of amino acid (Ser/Thr)-sp(2)-iminosugar glycomimetic conjugates featuring an α-O-linked pseudoanomeric linkage are reported. The key synthetic step involves the completely ...diastereoselective α-glycosylation of Ser/Thr due to strong stereoelectronic and conformational bias imposed by the bicyclic sp(2)-iminosugar scaffold. Mucin-related glycopeptides incorporating these motifs were recognized by the monoclonal antibody (mAb) scFv-SM3, with activities depending on both the hydroxylation pattern (Glc/Gal/GlcNAc/GalNAc) of the sp(2)-iminosugar and the peptide aglycone structure (Ser/Thr).
The reactivity of cyclic tertiary sulfamidates derived from α-methylisoserine strongly depends on the substitution at the C and N termini. These substrates are one of the very few examples able to ...undergo nucleophilic ring opening at a quaternary carbon with complete inversion of the configuration, as demonstrated both experimentally and computationally. When the sulfonamide is unprotected, the characteristic ring-opening reaction is completely silenced, which explains that the majority of the ring-opening reactions reported in the literature invoke N-alkyl or N-carbonyl-protected sulfamidates. Accumulation of negative charge at the NSO3 moiety in the transition state, especially when the sulfonamide NH is deprotonated, drastically raises the activation barrier for the nucleophilic attack. On the other hand, ester groups at the carboxylic position favor ring opening, whereas amides allow competition between the substitution and elimination pathways. Using pyridine as a nucleophilic probe, we have demonstrated both experimentally and computationally that a proper selection of the substitution scheme can enhance the synthetic scope of α-methylisoserine-derived sulfamidates, switching off and on the nucleophilic ring-opening in a controlled manner. This is particularly convenient for hybrid α/β-peptide synthesis, as demonstrated recently by our group.
A series of fluorescent d‐cysteines (Cys) has been synthesized and their optical properties were studied. The key synthetic step is the highly diastereoselective 1,4‐conjugate addition of aryl thiols ...to a chiral bicyclic dehydroalanine recently developed by our group. This reaction is fast at room temperature and proceeds with total chemo‐ and stereoselectivity. The Michael adducts were easily transformed into the corresponding amino acids to study their optical properties and, in some selected cases, into the corresponding N‐Fmoc‐d‐cysteine derivatives to be used in solid‐phase peptide synthesis (SPPS). To further demonstrate the utility of these non‐natural Cys‐derived fluorescent amino acids, the coumaryl and dansyl derivatives were incorporated into cell‐penetrating peptide sequences through standard SPPS and their optical properties were studied in different cell lines. The internalization of these fluorescent peptides was monitored by fluorescence microscopy.
Fluorescent d‐cysteines: The efficient synthesis of enantiopure and fluorescent d‐cysteines is reported by using highly chemo‐ and stereoselective S‐Michael additions of thiol‐containing dyes on a chiral bicyclic dehydroalanine. Their use as fluorescent labels was validated by incorporation into cell‐penetrating pentapeptides, which were treated with different HeLa cell lines, monitoring their internalization by fluorescence microscopy.
The Tn antigen (GalNAc-α-1- O -Thr/Ser) is a well-known tumor-associated carbohydrate determinant. The use of glycopeptides that incorporate this structure has become a significant and promising ...niche of research owing to their potential use as anticancer vaccines. Herein, the conformational preferences of a glycopeptide with an unnatural Tn antigen, characterized by a threonine decorated with an sp 2 -iminosugar-type α-GalNAc mimic, have been studied both in solution, by combining NMR spectroscopy and molecular dynamics simulations, and in the solid state bound to an anti-mucin-1 (MUC1) antibody, by X-ray crystallography. The Tn surrogate can mimic the main conformer sampled by the natural antigen in solution and exhibits high affinity towards anti-MUC1 antibodies. Encouraged by these data, a cancer vaccine candidate based on this unnatural glycopeptide and conjugated to the carrier protein Keyhole Limpet Hemocyanin (KLH) has been prepared and tested in mice. Significantly, the experiments in vivo have proved that this vaccine elicits higher levels of specific anti-MUC1 IgG antibodies than the analog that bears the natural Tn antigen and that the elicited antibodies recognize human breast cancer cells with high selectivity. Altogether, we compile evidence to confirm that the presentation of the antigen, both in solution and in the bound state, plays a critical role in the efficacy of the designed cancer vaccines. Moreover, the outcomes derived from this vaccine prove that there is room for exploring further adjustments at the carbohydrate level that could contribute to designing more efficient cancer vaccines.
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