C-glycosyl Amino Acid Research Articles

The preparation of C-glycosyl amino acids—an examination of olefin cross-metathesis

A study investigating the structural features directing olefin cross-metathesis to afford C-glycoamino acids was carried out. These results lead to an appreciation of the importance of proximal functionality to the relative reactivity of olefins in metathesis reactions providing a variable that is useful to suppress undesirable self-metathesis.

Stereocontrolled syntheses of α-C-mannosyltryptophan and its analogues

The total synthesis of alpha-C-mannosyltryptophan (C-Man-Trp), a naturally occurring C-glycosylamino acid, was achieved from a commercially available alpha-methyl-D-mannoside in 10 steps including the following key steps: the C-glycosidation of a mannose derivative with a stannylacetylene, Castro indole synthesis, and Sc(ClO4)3-promoted coupling with L-serine-derived aziridine carboxylate. The glucose- and galactose-analogues of C-Man-Trp were also synthesized in a similar manner. Conformational analyses of the synthesized C-glycosyltryptophan and its synthetic intermediate are briefly discussed.

Synthesis of C-glycosyl amino acids: scope and limitations of the tandem Tebbe/Claisen approach

Amino acids may be used as coupling partners for esterification with 3-hydroxy glycals as substrates for the tandem Tebbe/Claisen approach to the synthesis of C-glycosyl amino acids. Whilst esters of substituted α-amino acids do not successfully undergo Tebbe, or other, methylenation, esters of β- or γ-amino acids are methylenated to yield vinyl ethers, which then undergo smooth thermal rearrangement to yield β- C-glycoside products. tert-Butyl esters are found to be unreactive to the Tebbe reagent, and as such tert-butyl protection may be used for other carboxylic acids.

Synthesis and anti-tumor activity of β- C-glycoside analogs of the immunostimulant KRN7000

A ring-closing metathesis approach was employed for the synthesis of a β- C-glycoside analog of the immunostimulant KRN7000. The protected C-glycosyl amino acid derivative 18 was converted to amino-olefin 20 , and osmylation served to install the diol unit as a mixture of separable syn and anti isomers. Deprotection to the hydroxy-amine 21 was followed by N-acylation and debenzylation to deliver the target compound 5 .

Total synthesis of mannosyl tryptophan and its derivatives.

Glycosylation is one of the most important post- or co-translational modifications of proteins, which affects the biological activities of the parent proteins by influencing the higher-order structure. Recently, a highly novel variant of glycoproteins that incorporate a C-glycosylated amino acid was identified in various proteins. The total synthesis of one such C-glycosyl amino acid, namely, C (2)-alpha-D-C-mannosylpyranosyl-L-tryptophan and related peptides were successfully achieved. The mannose and tryptophan moieties were connected via ring opening of benzyl-protected 1,2-anhydro-mannose by a lithiated indole derivative. After the functional group conversion and deprotection steps, the glyco-amino acid was synthesized in a concise and stereoselective manner, in high overall yields. The stereoisomer, C (2)-alpha-D-C-glycosylpyranosyl-L-tryptophan was synthesized in a similar way. Furthermore, it was revealed that the intermediate azido acid can serve as a useful building block for peptide elongation. A synthetic route for the peptide bond formation of a glycopeptide, without protection of the hydroxyl groups, using the triazine salt derivative as a coupling reagent is also reported.

Synthesis of Ketosyl Spiro-isoxazolidine by 1,3-Dipolar Cycloaddition of 1-Methylenesugars with Nitrones Å|A New Access to C-Glycosyl Amino Acids

The 1,3-dipolar cycloaddition reactions of 1-methylenesugars (la-c) with nitrones (2 and 5) were carried out diastereoselectively under the catalysis of BF 3 .Et 2 O at low temperature and afforded the α-stereoselective spiro ketosyl isoxazolidines in good to excellent yields. The reductive isoxazolidine ring-opening of the spiro moiety with the treatment of zinc and acetic acid resulted in a new kind of C-glycosyl amino acid possessing a ketose form, providing an access to C-glycosyl amino acids. The structures of the synthesized compounds were confirmed by the spectroscopic analyses.

Synthesis of α‐ and β‐Glycosyl Asparagine Ethylene Isosteres (C‐Glycosyl Asparagines) via Sugar Acetylenes and Garner Aldehyde Coupling.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Development of Novel Methodology for Rapid Conjugated Oligosaccharide Synthesis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of alpha- and beta-glycosyl asparagine ethylene isosteres (C-glycosyl asparagines) via sugar acetylenes and Garner aldehyde coupling.

A convergent approach has been developed for the synthesis of C-glycosyl amino acids in which the glycinyl moiety CH(NH2)CO2H is connected to the anomeric center of the sugar residue by a three carbon atom tether. Essentially, these compounds are isosteres of N-glycosyl asparagines in which the amide group has been replaced by an ethylene bridge. Following the coupling of alpha- or beta-D-linked lithium C-glycoside acetylides with N-Boc D-serinal acetonide (Garner aldehyde), the resulting adducts were transformed into the final N-Boc-C-glycosyl-alpha-aminopentanoic acids via reduction of the triple bond, deoxygenation, and oxidative cleavage of the oxazolidine ring. By this protocol, 12 C-glycosyl asparagines, six pairs of alpha- and beta-anomers, have been prepared incorporating the gluco, galacto, manno, and the corresponding 2-acetamido-2-deoxy residues.

Development of novel methodology for rapid conjugated oligosaccharide synthesis

Glycosylation is one of the most important post-translation modifications of proteins, which affects biological activities by way of controlling higher order structure. Recently, the novel structure of glycoprotein, namely C-glycosyl protein was identified in various proteins. The first total synthesis of the naturally occurring C-glycosyl amino acid and peptide was achieved. The mannose and tryptophan moiety was connected via ring opening reaction of epoxide by lithiated indole derivative. After functional group conversion and deprotection, the glyco-amino acid was synthesized in a concise and stereoselective manner. To develop the rapid oligosaccharide construction methodology, the soluble polymer supported oligosaccharide was investigated. Due to high polarity of polymer support, the purification of PEG bound compound is achieved quite easily. The real-time monitoring of the glycosylation reaction was performed by MALDI-TOF MS, whereas the deprotection reaction of chloroacetyl group was performed by color test using (p-nitrobenzyl) pyridine. The purification of PEG bound compound which has chloroacetyl group, is achieved by capture-release strategy by use of resin bound cysteine derivative. By combination of these methodologies and novel linker, tetrasaccharides were synthesized.

A novel general route for the synthesis of C-glycosyl tyrosine analogues.

A general method for the synthesis of C-glycosyl amino acids is described here. The stereoisomerically pure tyrosine analogues alpha-L-4 and beta-L-6 are prepared in reasonable overall yields from allyl derivatives 10 and 11. The key step is a benzannulation procedure which is employed in the creation of the aromatic ring that bears the amino acid function.

A Ramberg−Bäcklund Approach to the Synthesis ofC-Glycosides,C-Linked Disaccharides, andC-Glycosyl Amino Acids

Synthetic applications of exo-glycals, derived from S-glycoside dioxides using the Meyers variant of the Ramberg−Bäcklund rearrangement, are described. These include a formal synthesis of a β-glycosidase inhibitor 12 and an efficient route to spirocyclic glucose derivatives 17 and 18. The synthesis of C-linked disaccharides 24, 31, and 38 and the C-glycosyl amino acid 49 using the Ramberg−Bäcklund rearrangement is also reported. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

INVESTIGATION OF THE SHARPLESS ASYMMETRIC AMINOHYDROXYLATION WITH C-ALLYL GLYCOSIDES

We have studied the Sharpless asymmetric aminohydroxylation on C-allyl glycosides in order to prepare C-glycosyl aminoacids or C-glycopeptides. The perbenzylated amino α-C-allyl glucoside 1 and β-C-allyl glucoside 2 were shown to be moderate substrates for this reaction. New C-glycosyl α-amino ketones were isolated after oxidation of the crude β-amino alcohols.

Chiral auxiliary based approach toward the synthesis of C-glycosylated amino acids.

[reaction in text] In a chiral auxiliary based method C-glycosylated amino acids can be obtained by a 1,3-dipolar cycloaddition of a chiral glycine equivalent and C-1 allyl- or vinyl-derived carbohydrate building blocks as the key step. The products are formed regio- and diastereoselectively. Reductive cleavage of the N-O bond of the isoxazolidine and of the chiral auxiliary leads to C-glycosylated amino acids. The use of (-)-menthone to (+)-menthone as the auxiliary leads to the corresponding diastereomers.

A concise C-glycosyl amino acid synthesis by alkenyl C-glycoside–vinyloxazolidine cross-metathesis. Synthesis of glycosyl serine, asparagine and hydroxynorvaline isosteres

A convergent synthesis has been developed to afford C-linked glycosyl amino acids by cross-metathesis of vinyl, allyl, and butenyl C-glycosides with N-Boc-vinyloxazolidine using the Grubbs 1,3-dimesityl-4,5-dihydroimidazol-2-ylideneruthenium carbene. The method has been employed to introduce through an α-linkage, an α-aminopentanoic acid chain at the anomeric carbon of β-D-C-gentiobiose to give a totally artificial glycosyl α-amino acid of a disaccharide. This compound represents the isostere of the α-linked glycosylasparagine moiety of the natural glycopeptide nephritogenoside.

Total Synthesis of α-C-Mannosyltryptophan, a Naturally Occurring C-Glycosyl Amino Acid

Total Synthesis of α-C-Mannosyltryptophan, a Naturally Occurring C-Glycosyl Amino Acid

Formylation of carbohydrates and the evolution of synthetic routes to artificial oligosaccharides and glycoconjugates

Abstract A highly effective method for the synthesis of formyl C-glycosides is described via addition of 2-lithiothiazole or 2-lithiobenzothiazole to sugar lactones, deoxygenation of the resulting ketols, and releasing of the formyl group from the heterocyclic ring. The synthetic utility of these sugar aldehydes is demonstrated by the development of synthetic methods to more elaborate C-glycosides. These include various (1-6)-C-disaccharides and some higher oligomers up to a C,C,C,C-pentasaccharide; C-glycosyl amino acid isosteres of N-glycosyl asparagines; the methylene isostere of β-Δ-galactosyl ceramide; linear and cylic (2-1)-ketoside oligomers. An alternative synthesis of ethylene-bridged glycosyl asparagine isosteres is illustrated by the use of ethynyl C-glycosides as starting materials.

Diastereoselective Synthesis of C-Glycosylated Amino Acids with Lactams as Peptide Building Blocks

Readily available by lipase-catalyzed kinetic resolution or from a chiral pool, β-, γ-, and δ-lactams can be used as peptide building blocks for the synthesis of C-glycosylated amino acids 1. By reaction with glycosyl dianions, metabolic stable glycosylated amino acids can be prepared diastereoselectively. Ac=acetyl; Bn=benzyl; Boc=tert-butoxycarbonyl; R=Et, Bn; R′=H, alkyl; n=1–3.

Diastereoselective Synthesis of C-Glycosylated Amino Acids with Lactams as Peptide Building Blocks

Readily available by lipase-catalyzed kinetic resolution or from a chiral pool, beta-, gamma-, and delta-lactams can be used as peptide building blocks for the synthesis of C-glycosylated amino acids 1. By reaction with glycosyl dianions, metabolic stable glycosylated amino acids can be prepared diastereoselectively. Ac=acetyl; Bn=benzyl; Boc=tert-butoxycarbonyl; R=Et, Bn; R'=H, alkyl; n=1-3.

Synthesis of C-Glycosyl Lactones and Protected C-Glycosyl Amino Acids: Use of Radical Cyclization.

Protected carbohydrates 6a-13a, having one free hydroxyl and a phenylseleno group or halogen on the adjacent carbon, were condensed with (2,2-diphenylhydrazono)acetic acid (2); the resulting esters undergo radical cyclization to afford carbohydrates fused to a 2,2-diphenylhydrazino lactone unit (6c,d-13c,d). In suitable cases (9c,d) such carbohydrate lactones can be elaborated into C-glycosyl amino acids.