Unexpected loss of stereoselectivity in glycosylation reactions during the synthesis of chondroitin sulfate oligosaccharides

• Teresa Mena-Barragán,
• José L. de Paz and
• Pedro M. Nieto

Beilstein J. Org. Chem. 2019, 15, 137–144, doi:10.3762/bjoc.15.14

• buffer afforded compound 2. With the required disaccharide building blocks in hand, the synthesis of tetrasaccharide 14β was attempted using catalytic TMSOTf in CH2Cl2 at 0 ºC (Scheme 4). After F-SPE, two spots were detected in the TLC analysis of the fluorous containing fraction, in addition to

• for the synthesis of CS oligomers. A fully deprotected tetrasaccharide was successfully prepared for biological studies. This synthesis involved the [2 + 2] coupling of disaccharide building blocks. The use of a fluorous tag facilitated the isolation of the fluorinated species from the glycosylation

Preactivation-based chemoselective glycosylations: A powerful strategy for oligosaccharide assembly

• Weizhun Yang,
• Bo Yang,
• Sherif Ramadan and
• Xuefei Huang

Beilstein J. Org. Chem. 2017, 13, 2094–2114, doi:10.3762/bjoc.13.207

• synthesis of libraries of oligosaccharides by divergently combining building blocks. An example of this is the preparation of a library of heparan sulfate oligosaccharides (Figure 8) [74]. Alternating use of disaccharide building blocks 127 and 128 in preactivation-based one-pot glycosylation led to a panel

Intramolecular glycosylation

• Xiao G. Jia and
• Alexei V. Demchenko

Beilstein J. Org. Chem. 2017, 13, 2028–2048, doi:10.3762/bjoc.13.201

• debenzylation followed by global acetylation to afford product 30. The extension of this approach to convergent oligosaccharide synthesis and reiterative sequencing in presented in Scheme 8. Thus, maltose and lactose disaccharide building blocks were linked via the xylylene tether, and the resulting compound 31

Automated glycan assembly of a S. pneumoniae serotype 3 CPS antigen

• Markus W. Weishaupt,
• Stefan Matthies,
• Mattan Hurevich,
• Claney L. Pereira,
• Heung Sik Hahm and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2016, 12, 1440–1446, doi:10.3762/bjoc.12.139

• oligosaccharide mixture of different chain lengths and frame shifts. Access to defined synthetic S. pneumoniae CPS structures is desirable. Known syntheses of S. pneumoniae serotype 3 CPS rely on a time-consuming and low-yielding late-stage oxidation step, or use disaccharide building blocks which limits

• . Disaccharide building blocks containing glucuronic acid were used by de Jong et al. to prepare two different SP 3 trisaccharides [24]. In general, the late-stage-oxidation approach is often preferred since it circumvents the inherent reactivity issues associated with uronic acid building blocks [25][26][27

Automated solid-phase synthesis of oligosaccharides containing sialic acids

• Chian-Hui Lai,
• Heung Sik Hahm,
• Chien-Fu Liang and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2015, 11, 617–621, doi:10.3762/bjoc.11.69

• incorporation of sialic acid–galactose disaccharide building blocks [5][11]. Here, we describe a sialic acid building block that can be utilized for automated glycan assembly. Results and Discussion Sialylating oligosaccharides in high yield and α-selectivity was challenging since the presence of a C-1 carboxyl

Automated synthesis of sialylated oligosaccharides

• Davide Esposito,
• Mattan Hurevich,
• Bastien Castagner,
• Cheng-Chung Wang and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2012, 8, 1601–1609, doi:10.3762/bjoc.8.183

• sialyl α-(2→3) and α-(2→6) galactosyl imidates, which, used in combination with the automated platform, provided rapid access to a small library of conjugation-ready sialosides of biological relevance. Keywords: automated synthesis; disaccharide building blocks; solid-phase synthesis; sialic acid

• platform [5]. Central to the success of this approach is the use of galactals as nucleophiles for chemical sialylation, which allows for efficient access to the novel sialyl α-(2-3) and α-(2-6) galactosyl imidate disaccharide building blocks. The combination of the automated platform and sialylated

• disaccharide building blocks 4 and 5. It should be noted that building block 4 can be prepared with higher overall yield than the recently disclosed N-Troc protected disaccharide building block [11] obtained with a similar method. Solution-phase studies In order to evaluate the utility of building block 4 for