(2-Nitrophenyl)acetyl: a new, selectively removable hydroxyl protecting group

Electrosynthesis of Spiro-indolenines via Dearomative Arylation of Indoles in Batch and Continuous Flow

An electrosynthesis of spiro-indolenines in batch and continuous flow was achieved through dearomative arylation of indoles with good functional group compatibility. User-friendly undivided cells were used under catalyst- and oxidant-free conditions. Moreover, the use of a flow electrolysis cell gave high daily productivity and excellent scale-up potential under less supporting electrolyte and higher substrate concentration conditions.

Broadening the Scope of the Reverse Orthogonal Strategy for Oligosaccharide Synthesis

The reverse orthogonal strategy was invented in 2011 in an attempt to address drawbacks of other strategies for glycan assembly. Different from the classical orthogonal approach that relies on the orthogonality of leaving groups, the reverse strategy is based on orthogonal protecting groups that could be removed during the glycosylation step. This strategy remained largely unexplored due to only one combination of orthogonal protecting groups that would fit into this concept. Reported herein are new orthogonal combinations of leaving and protecting groups that help to streamline the glycan assembly. Also reported is further refinement of the previously reported reaction conditions.

Cyanomethyl (CNMe) ether: an orthogonal protecting group for saccharides

Logical manipulation of protecting groups is one of the vital strategies involved in the synthesis of complex oligosachharides. As opposed to the robust permanent protecting groups, the chemoselective protection-deprotection processes on orthogonal protecting groups have facilitated the synthesis of the target molecules with higher effeciency. While the derivatives of benzyl ethers are the most popular orthogonal ether based protecting groups for hydroxyls, the exploration of methyl ethers for similar synthetic application is much limited. We herein report cyanomethyl (CNMe) ether as a readily synthesized orthogonal protecting group for saccharides. The ether moiety was rapidly removed under Na-naphthalenide conditions in good to excellent yields and was found to be compatible with other well-known benzyl/methyl/silyl ether and acetal protecting groups. Additionally, the CNMe group was observed to be tolerant to standard reagents used for the deprotection of ether, ester and acetal protecting groups. The protection and deprotection steps remained unaffected by the position of hydroxyl, the configuration of monosaccharides or the presence of olefins in the skeleton.

Triethylamine-methanol mediated selective removal of oxophenylacetyl ester in saccharides

A highly selective, mild, and efficient method for the cleavage of oxophenylacetyl ester protected saccharides was developed using triethylamine in methanol at room temperature. The reagent proved successful against different labile groups like acetal, ketal, and PMB and also generated good yields of the desired saccharides bearing lipid esters. Further, we also observed DBU in methanol as an alternative reagent for the deprotection of acetyl, benzoyl, and oxophenylacetyl ester groups.

Synthetic Carbohydrate Chemistry and Translational Medicine

The importance of post-translational glycosylation in protein structure and function has gained significant clinical relevance recently. The latest developments in glycobiology, glycochemistry, and glycoproteomics have made the field more manageable and relevant to disease progression and immune-response signaling. Here, we summarize the current progress in glycoscience, including the new methodologies that have led to the introduction of programmable and automatic as well as large-scale enzymatic synthesis, and the development of glycan array, glycosylation probes, and inhibitors of carbohydrate-associated enzymes or receptors. These novel methodologies and tools have facilitated our understanding of the significance of glycosylation and development of carbohydrate-derived medicines that bring the field to the next level of scientific and medical significance.

The 2,2-Dimethyl-2-(ortho-nitrophenyl)acetyl (DMNPA) Group: A Novel Protecting Group in Carbohydrate Chemistry

The 2,2-dimethyl-2-(ortho-nitrophenyl)acetyl (DMNPA) group was introduced to synthetic carbohydrate chemistry as a protecting group (PG) for the first time. Benefiting from a unique chemical structure and novel deprotection conditions, the DMNPA group can be cleaved rapidly and mutually orthogonal to other PGs. Orchestrated application of the DMNPA group with other PGs led to the highly efficient synthesis of the glycan of thornasterside A.

2-O-Benzyloxycarbonyl protected glycosyl donors: a revival of carbonate-mediated anchimeric assistance for diastereoselective glycosylation

Benzyloxycarbonyl can be used as participating group for the diastereoselective glycosylation of base-labile products and the synthesis of glycosyl esters.

2-Methoxyphenyl isocyanate: a chemoselective multitasking reagent for an amine protection/deprotection sequence

Organic amines protected through urea bond mediated capping.

Chemical Glucosylation of Labile Natural Products Using a (2-Nitrophenyl)acetyl-Protected Glucosyl Acetimidate Donor

The synthesis of (2-nitrophenyl)acetyl (NPAc)-protected glucosyl donors is described that were designed for the neighboring-group assisted glucosylation of base-labile natural products also being sensitive to hydrogenolysis. Glycosylation conditions were optimized using a trichloroacetimidate glucosyl donor, and cyclohexylmethanol and (+)-menthol as model acceptors. The approach was then extended to a one-pot procedure for the synthesis of 1,2-trans-glycosides. This method was finally applied for improved synthesis of the masked mycotoxin T2-O-β,d-glucoside.

A new method testing the orthogonality of different protecting groups

A new test was elaborated to identify a new set of orthogonal protecting groups. With the developed method eight different protecting groups were tested under various deprotection conditions and the complex reaction mixtures were analysed by HPLC. The developed method allows for quick identification of orthogonality using simple model structures.

Synthesis of a chlorogenin glycoside library using an orthogonal protecting group strategy

Naturally occurring spirostanol saponins bear a chacotriose, α-L-rhamnopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→4)]-β-D-glucopyranose residue as the oligosaccharide moiety which is believed to be important for biological activity. Herein the development of a concise, combinatorial method for the synthesis of two series of glycan variants at the 2' and/or 4' positions of chacotriose is described and the structure-activity relationships of the glycone part at 3-OH of chlorogenin investigated. These compounds were found to be weakly-cytotoxic toward leukemia cell lines CCRF and HL-20, indicating that the chacotriose moiety is important for anticancer activity.

Transformation of the (2-nitrophenyl)acetyl protecting group in the presence of trichloroacetonitrile and 1,8-diazabicyclo[5,4,0]-undec-7-ene

When treated with trichloroacetonitrile in the presence of 1,8-diazabicyclo[5,4,0]-undec-7-ene, the (2-nitrophenyl)acetyl protecting group (NPAc) was partially transformed into mono-(NPClAc) and dichlorinated (NPCl₂Ac) species, but no chlorination occurred in the presence of solid potassium carbonate. The monochlorinated NPClAc group, which is suitable for use in glycosylation reaction, can be selectively removed by treatment with thiourea.