Glycosylation via locked anomeric configuration: stereospecific synthesis of oligosaccharides containing the β-d-mannopyranosyl and β-l-rhamnopyranosyl linkage11For a preliminary account of this work, see ref. [7].

Synthesis of an Alkyne‐Modified Bleomycin Disaccharide Precursor, Conversion to a 18F‐Labeled Radiotracer, and Preliminary in vivo‐PET Imaging Studies

“…Diphenyl Phosphate (1): A solution of nBuLi (4.4 mL, 11 mmol, 2.5 M in hexane) was added to a stirred solution of 3-O-benzyl-2,4,6-tri-Oacetyl-D-mannopyranose [12,14,15] (3.6 g, 9.1 mmol) in anhydrous THF (27 mL) at -78°C. The resulting solution was stirred for 10 min at -78°C before the addition of diphenyl chlorophosphate (2.3 mL, 11 mmol).…”

“…1,6-Anhydro-3,4-di-O-benzoyl--L-gulopyranoside (2) and 2,4,6tri-O-acetyl-3-O-benzyl-α-D-mannopyranosyl diphenyl phosphate (1) were first prepared following the published procedures. [12][13][14][15] Glycosylation of 2 with 1 in the presence of TMSOTf catalyst gave the desired 2-O-(α-D-mannopyranosyl)-L-gulose (6) in 76 % yield. The 1,6-anydro linkage was cleaved/acetylated using acetic anhydride in the presence Cu(OTf ) 2 -catalyst (7, 94 %) and the benzyl protection of the mannose unit was selectively and quantitatively removed by hydrogenolysis using Pd(OH) 2 as a catalyst (8).…”

“…Prior to the 18 F-labeling, precursor 11 (as an anomeric mixture) was quantitatively converted into the alkyne modified BLM disaccharide 12 using 6N ammonia in dry methanol, followed by filtration through a C- 250 × 10 mm, 10 μm, 90 Å) equipped with a radio detector (Scheme 2B). The retention times of the product (13) and starting material (15) were additionally compared to a LC-MS data of the corresponding "cold reaction" [i.e. 1-azido-2-(2-{2-[2-( 19 F)fluoroethoxy]ethoxy}ethoxy)ethane used for the same reaction, Scheme 2C].…”

Studies towards a Conjugate Vaccine for Anthrax: Synthesis of the Tetrasaccharide Side Chain of the Bacillus anthracis Exosporium

“…The initial glycosyl acceptor 5 was synthesized from the triflate 4 of benzyl 6-hydroxyhexanoate (3) [6] and the stannylidene acetal 2 of 3,4-di-O-benzyl-L-rhamnose (1) [7] (Scheme 1). The formation of the b-L-rhamnopyranosyl linkage was stereospecific [8] [9], as manifested [10] in the 1 H-coupled 13 C-NMR spectrum of the sole glycoside formed (J(C(1),HÀ C(1)) = 156.4 Hz). To introduce the spacer, we preferred the use of benzyl ester 3 to the more commonly employed analogous methyl ester [11] since triflation of 3 (!…”

Stereoselective Construction of β‐Mannopyranosides by AnomericO‐Alkylation: Synthesis of the Trisaccharide Core ofN‐linked Glycans

“…Previously,S chmidt and co-workers reported limited studies on anomeric O-alkylation of partially or fully protected d-mannopyranoses with simple primary electrophiles under various reaction conditions. [28c,d] In their experiments either poor to moderate yields [28c] or moderate selectivity [28d] was observed when either NaH or KO t Bu was used as the base.W hen3 ,4,6-tri-O-benzyl-d-mannopyranose (see 1a in Table 1) was employed, over-alkylation was found to be ap roblem.[28c] Some success was also achieved by others [30] when 1a or other partially protected d-mannopyranoses were converted into their corresponding 1,2-O-dibutylstannylene complexes followed by O-alkylation with various electrophiles.However,organostannanes are highly toxic and the use of stoichiometric amounts of organostannanes is certainly not desirable.In consideration of the natural b-(1!4)-linked mannopyranosidic linkage in complex N-linked glycans,wechose to study the anomeric O-alkylation reaction between 1a and the d-galactose-derived C4 secondary triflate 6a for selective production of the corresponding b-mannopyranoside 7 (Table 1). Initially,w ea pplied the optimal reaction conditions,w hich we had discovered previously, [24,27] for the synthesis of 2-deoxy glycosides to this type of b-mannopyranosylation.…”