One-pot Oligosaccharide Synthesis Research Articles

Synthesis of Superarmed Thioglycosides via the Ring Opening of 1,2-Orthoesters

AbstractSince the advent of the armed–disarmed strategy, thioglycosides have become essential tools in one-pot oligosaccharide synthesis. The continuum of glycosyl donor reactivity has since been expanded to include so-called ‘superarmed’ thioglycoside donors whose reactivity relies on more than just the inductive effects of protecting groups. Here we report a new method for the synthesis of superarmed thioglycosides via the ring opening of 1,2-orthoesters. This method ensures the necessary 1,2-trans stereochemistry, and importantly, makes use of trimethylsilyl thioethers as sulfur nucleophiles to avoid the use of unpleasant free thiols. Ten examples of ethyl and phenyl thioglycosides of mono- and disaccharides were synthesised from their orthoesters using tris(pentafluorophenyl)borane (BCF) as the Lewis acid promoter and were obtained in good yield and purity.

Hierarchical and Programmable One-Pot Oligosaccharide Synthesis.

This article presents a general experimental protocol for programmable one-pot oligosaccharide synthesis and demonstrates how to use Auto-CHO software for generating potential synthetic solutions. The programmable one-pot oligosaccharide synthesis approach is designed to empower fast oligosaccharide synthesis of large amounts using thioglycoside building blocks (BBLs) with the appropriate sequential order of relative reactivity values (RRVs). Auto-CHO is a cross-platform software with a graphical user interface that provides possible synthetic solutions for programmable one-pot oligosaccharide synthesis by searching a BBL library (containing about 150 validated and >50,000 virtual BBLs) with accurately predicted RRVs by support vector regression. The algorithm for hierarchical one-pot synthesis has been implemented in Auto-CHO and uses fragments generated by one-pot reactions as new BBLs. In addition, Auto-CHO allows users to give feedback for virtual BBLs to keep valuable ones for further use. One-pot synthesis of stage-specific embryonic antigen 4 (SSEA-4), which is a pluripotent human embryonic stem cell marker, is demonstrated in this work.

One-pot oligosaccharide synthesis: latent-active method of glycosylations and radical halogenation activation of allyl glycosides

Abstract Chemical glycosylations occupy a central importance to synthesize tailor-made oligo- and polysaccharides of functional importance. Generation of the oxocarbenium ion or the glycosyl cation is the method of choice in order to form the glycosidic bond interconnecting a glycosyl moiety with a glycosyl/aglycosyl moiety. A number of elegant methods have been devised that allow the glycosyl cation formation in a fairly stream-lined manner to a large extent. The latent-active method provides a powerful approach in the protecting group controlled glycosylations. In this context, allyl glycosides have been developed to meet the requirement of latent-active reactivities under appropriate glycosylation conditions. Radical halogenation provides a newer route of activation of allyl glycosides to an activated allylic glycoside. Such an allylic halide activation subjects the glycoside reactive under acid catalysis, leading to the conversion to a glycosyl cation and subsequent glycosylation with a number of acceptors. The complete anomeric selectivity favoring the 1,2-trans-anomeric glycosides points to the possibility of a preferred conformation of the glycosyl cation. This article discusses about advancements in the selectivity of glycosylations, followed by delineating the allylic halogenation of allyl glycoside as a glycosylation method and demonstrates synthesis of a repertoire of di- and trisaccharides, including xylosides, with varied protecting groups.

Hierarchical and programmable one-pot synthesis of oligosaccharides

The programmable one-pot oligosaccharide synthesis method was designed to enable the rapid synthesis of a large number of oligosaccharides, using the software Optimer to search Building BLocks (BBLs) with defined relative reactivity values (RRVs) to be used sequentially in the one-pot reaction. However, there were only about 50 BBLs with measured RRVs in the original library and the method could only synthesize small oligosaccharides due to the RRV ordering requirement. Here, we increase the library to include 154 validated BBLs and more than 50,000 virtual BBLs with predicted RRVs by machine learning. We also develop the software Auto-CHO to accommodate more data handling and support hierarchical one-pot synthesis using fragments as BBLs generated by the one-pot synthesis. This advanced programmable one-pot method provides potential synthetic solutions for complex glycans with four successful examples demonstrated in this work.

Synthetic avenues towards a tetrasaccharide related to Streptococcus pneumonia of serotype 6A.

Streptococcus pneumonia (SPn) is a Gram-positive bacterium which causes life threatening diseases. The bacteria protect themselves against non-specific host defence by an external polysaccharide (PS) capsule which bears a repeating unit, α-D-Galp(1->3)-α-D-Glcp(1->3)-α-L-Rhap(1->3)-D-Rib (SPn 6A). A closer look at the structure reveals the presence of α-linked galactose and glucose residues. The synthesis of these 1,2-cis glycosidic linkages are considered challenging particularly in the context of a one-pot oligosaccharide synthesis. We have synthesized the aforesaid tetrasaccharide (SPn 6A) based on both stepwise and sequential one-pot glycosylation reactions using easily accessible common building blocks; eventually similar overall yields were obtained in both cases.

2-Pyridyl glycoside: an alternative glycosyl donor in preactivation protocol

2-Pyridyl glycosides have been identified to be powerful glycosyl donors for the preactivation-based oligosaccharide synthesis. By using stoichiometric amount of Tf2O, the 2-pyridyl glycosides were pre-activated, which subsequently underwent glycosylation reactions smoothly to produce the coupled products in high yields. Furthermore, the 2-pyridyl glycosides were applied to the efficient oligosaccharide assembly by the preactivation-based one-pot oligosaccharide synthesis protocol.

ChemInform Abstract: In situ Formation of β‐Glycosyl Imidinium Triflate from Participating Thioglycosyl Donors: Elaboration to Disarmed—Armed Iterative Glycosylation

Abstract16 examples for disaccharides, 3 examples for trisaccharides

In situ formation of β-glycosyl imidinium triflate from participating thioglycosyl donors: elaboration to disarmed–armed iterative glycosylation

β-Glycosyl imidinium triflate is generated from participating thioglycoside donors for disarmed-armed iterative glycosylations and one-pot oligosaccharide synthesis.

Solvent Participation in a One-Pot Glycosylation Strategy (SPOG)

Solvent participation in a one-pot glycosylation strategy (SPOG) was developed on the basis of the low concentration β-selective glycosylation method. This strategy enables the production of a β-glycosidic bond in a one-pot oligosaccharide synthesis without or with minimal use of any C-2 participating function.

Programmable reactivity-based one-pot oligosaccharide synthesis

A detailed protocol is described for the application of a programmable one-pot oligosaccharide synthesis methodology to the synthesis of fucosyl GM1. This serves as a general example of the application of this method to the synthesis of any desired oligosaccharide. The method relies on a large database of relative reactivities for differentially protected tolyl thioglycoside donor molecules and a computer program to suggest the best order of addition for assembly of the oligosaccharide in optimal yield and with the fewest operations. The product is a protected form of the desired oligosaccharide isolated in 47% yield, which is then deprotected using standard procedures to provide fucosyl GM1 oligosaccharide (1) in 44% yield. The total time for synthesis of 1 from building blocks 3, 4 and 5 is approximately 4 d, whereas synthesis of the same compound by traditional stepwise procedures would take significantly longer. Protocols for the synthesis of thioglycoside building blocks 3 and 4 are also described.

N-Benzyl-2,3-oxazolidinone as a Glycosyl Donor for Selective α-Glycosylation and One-Pot Oligosaccharide Synthesis Involving 1,2-cis-Glycosylation

Glycosylation reactions using N-benzyl-2,3-trans-oxazolidinones as the glycosyl donors were shown to be highly alpha-selective. Advantages of the donor include facile preparation in gram-scale preparation and simple deprotection procedures. Subsequently, a one-pot oligosaccharide synthesis involving 1,2-cis glycosidic linkages was demonstrated using the novel glycosyl donors.

N‐(Phenylthio)‐ε‐caprolactam: A New Promoter for the Activation of Thioglycosides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

N-(phenylthio)-epsilon-caprolactam: a new promoter for the activation of thioglycosides.

N-(phenylthio)-epsilon-caprolactam (1) has been applied as a new promoter for the activation of thioglycosides. This proceeds by the reaction of 1 with trifluoromethansulfonic anhydride, which subsequently activates the thioglycoside for glycosidic bond formation. Notably, the reaction proceeds efficiently at room temperature and is adaptable to our reactivity-based one-pot oligosaccharide synthesis. [reaction: see text]

A programmable one-pot oligosaccharide synthesis for diversifying the sugar domains of natural products: a case study of vancomycin.

A programmable one-pot oligosaccharide synthesis for diversifying the sugar domains of natural products: a case study of vancomycin.

One-pot oligosaccharide synthesis exploiting solvent reactivity effects.

[reaction: see text] One-pot syntheses of trisaccharides have been accomplished simply by changing the solvent system between the two subsequent glycosylation reactions and utilizing the difference in glycosylation rate between different solvents. By tuning the reactivity of acceptors and donors and performing the first glycosylation in Et(2)O (low glycosylation rate) and the second in CH(2)Cl(2)/Et(2)O (higher glycosylation rate), trisaccharides were synthesized in high yields (76-84%).

Anomeric reactivity-based one-pot oligosaccharide synthesis: a rapid route to oligosaccharide libraries.

The assembly of an oligosaccharide library has been achieved in a practical and efficient manner employing a' one-pot sequential approach. With the help of the anomeric reactivity values of thioglycosides, using a thioglycoside (mono- or disaccharide) with one free hydroxyl group as acceptor and donor coupled with another fully protected thioglycoside, a di- or trisaccharide is selectively formed without self-condensation and subsequently reacted in situ with an anomerically inactive glycoside (mono- or disaccharide) to form a tri- or tetrasaccharide in high overall yield. The approach enables the rapid assembly of 33 linear or branched fully protected oligosaccharides using designed building blocks. These fully protected oligosaccharides have been partially or completely deprotected to create 29 more structures to further increase the diversity of the library.