Karl Jansson

Boron trifluoride etherate as an effective reagent for the stereoselective one-pot conversion of acetylated 2-trimethylsilylethyl glycosides into sugar 1,2-trans-acetates

Summary Treatment of 2-trimethylsilylethyl glycosides with boron trifluoride etherate in the presence of acetic anhydride gave the corresponding sugar acetate in >90% isolated yield and with a 1,2- trans : cis ratio of >20:1. The sugar with a free anomeric hydroxyl group was obtained when acetic anhydride was omitted.

Synthetic receptor analogues: preparation of the 3-O-methyl, 3-C-methyl, and 3-deoxy derivatives of methyl 4-O-α-D-galactopyranosyl-β-D-galactopyranoside (methyl β-D-galabioside)

Abstract Methyl β- d -galactopyranoside was transformed into methyl 2- O -benzyl- ( 5 , 24%) and 2- O -benzyloxymethyl-4,6- O -benzylidene-β- d -galactopyranoside ( 8 , 60%) in two and four steps respectively. Compounds 5 and 8 were then transformed into the corresponding 3- O -methyl, 3- C -methyl, and 3-deoxy derivatives variously by O -methylation, Wittig olefination/stereospecific hydrogenation, and xanthate reduction. Regioselective reductive opening of the 4,6- O -benzylidene rings gave galactoside derivatives with HO-4 unsubstituted. Bromide-ion catalysed α- d -galactosidation and hydrogenolysis of the benzyl protecting-groups then gave the desired β- d -galabioside analogues.

Synthetic receptor analogues: preparation and calculated conformations of the 2-deoxy, 6-O-methyl, 6-deoxy, and 6-deoxy-6-fluoro derivatives of methyl 4-O-α-d-galactopyranosyl-β-d-galactopyranoside (methyl β-d-galabioside)☆

Abstract The 2-deoxy (7), 6-O-methyl (15), 6-deoxy (22), and 6-deoxy-6-fluoro (31) derivatives of methyl β- d -galabioside (1) have been synthesised. Thus, 7 was prepared by xanthate reduction using tributyltin hydride, whereas 22 was obtained by catalytic hydrogenation of a 6-deoxy-6-iodogalabioside. Regioselective mono-fluorination of methyl 2,3-di-O-benzoyl-β- d -galactopyranoside with Et2NSF3 and subsequent α- d -galactosylation provided 31. Molecular mechanics calculations yielded similar conformations for 1, 7, 15, 22, and 31 with differes in φH and ψH of 5°. No indications of intramolecular hydrogen bonds, as displayed by 1 in the crystal, were found for 7, 15, 22, or 31.

2-Trimethylsilylethyl glycosides. Anomeric deblocking of mono- and disaccharides

Abstract Anomeric deblocking of acetylated, benzylated and unprotected 2-trimethylsilylethyl (TMS-ethyl) glycosides was effected by treatment with trifluoroacetic acid/dichloromethane at 0–25°C for 10–30 min. The yield of deblocked and purified mono- and disaccharides varied between 90 and 95%.

Preparation and calculated conformations of the 2′-, 3′-, 4′-, and 6′-deoxy, 3′-O-methyl, 4′-epi, and 4′- and 6′-deoxyfluoro derivatives of methyl 4-O-α-d-galactopyranosyl-β-d-galactopyranoside (methyl β-d-galabioside)

Abstract The glycosyl chlorides of the 3- O -methyl ( 6 ) and 4-deoxy-4-fluoro ( 8 ) O -benzylated derivatives of d -galactopyranose and 2,3,4,6-tetra- O -benzyl- d -glucopyranose were condensed with methyl 2,3,6-tri- O -benzoyl-β- d -galactopyranoside to give, after deprotection, the 3′- O -methyl ( 23 ), 4′-deoxy-4′-fluoro ( 25 ), and 4′-epi ( 27 ) derivatives, respectively, of methyl β- d -galabioside ( 1 ). The glycosyl fluorides of 2,3,4-tri- O -benzyl- d -fucopyranose and the 3-deoxy ( 12 ) and 4-deoxy ( 16 ) O -benzylated derivatives of d -galactopyranose were condensed with methyl 2,3,6-tri- O -benzyl-β- d -galactopyranoside ( 21 ), to give, after deprotection, the 6′-deoxy ( 31 ), 3′-deoxy ( 34 ), and 4′-deoxy ( 37 ) derivatives of 1 , respectively. The 2′-deoxy ( 41 ) derivative of 1 was prepared by N -iodosuccinimide-induced condensation of 3,4,6-tri- O -acetyl- d -galactal and 21 followed by deprotection. Treatment of methyl 2,3,6-tri- O -benzoyl-4- O -(2,3-di- O -benzoyl-α- d -galactopyranosyl)-β- d -galactopyranoside with Et 2 NSF 3 (DAST), followed by deprotection, provided the 6′-deoxy-6′-fluoro ( 46 ) derivative of 1 . Molecular mechanics calculations yielded conformations for 23, 25, 27, 31, 34, 37, 41, and 46 with small deviations from the calculated conformation for 1 (Φ H /Ψ H : −40°/−6°).

Gas Chromatographic Investigation of the Boron Trifluoride Etherate-Induced Formation and Anomerization of Glucopyranosides

Abstract Boron trifluoride etherate-induced glucosylation of methanol, 1-propanol, 2-propanol, 2-bromoethanol, and 3-bromo-2-(bromomethyl)propan-1-ol, using 1,2,3,4,6-penta-O-acetyl-β-D-glucopyranose as donor, gave the corresponding β-glucopyranosides. The α-glucosides and 1,2,3,4,6-penta-O-acetyl-α-D-glucopyranose were formed as byproducts in varying amounts, according to GLC analysis. The propensity of the different glucopyranosides to anomerize was determined in separate experiments. 1. Dedicated to the memory of Professor Akira Hasegawa.

Unexpected formation of the 3,6-anhydro and 6-O-methyl-1-fluoro derivatives of galabiose on attempted substitution of HO-6 by fluorine in methyl 4-O-α-d-galactopyranosyl-β-d-galactopyranoside (methyl β-d-galabioside)

Preparation de desoxy-6 fluoro-6 β-D-galabioside de methyle a partir de O-methyl-1 β-D-galabioside. Il se forme aussi les composes non attendus du titre

2-Trimethylsilylethyl glycosides: treatment with electrophilic reagents to give trimethylsilyl- and methoxymethyl glucopyranosides and glucopyranosyl chloride

Abstract Treatment of 2-trimethylsilylethyl 2346-tetra-O-acetyl-β-D-glucopy ranoside (-1) with trimethylsilyl trifluoromethanesulfonate trifluoromethanesulfonic acid or borontrifluoride etherate in the presence ofdimethoxymethane gave methoxymethyl 2346-tetra-O-acetyl-β-D-glucopyranoside in 54 62 and 66% yield respectively. In the absence of dimethoxymethane trimethylsilyl 2346-tetra-O-acetyl-β-D-glucopyranoside was formed in 78% yield. Treatment of I with 11-dichloromethylmethyl ether in the presence of zinc chloride gave 2346-tetra-O-acetyl-α-D-glucopyranosyl chloride in 98% yield.

Radially resolved simulations of collapsing pebble clouds in protoplanetary discs

In the Solar System, asteroids and Kuiper belt objects as well as comets are remnant planetesimals from the time of planet formation. Interactions between solids and gas inside a protoplanetary disc can, e.g. through the streaming instability, form gravitationally bound planetesimal-mass clouds of pebbles. Such clouds will inevitably have inelastic collisions between pebbles, lose energy and experience a runaway collapse into planetesimals. We study the collapse process with a statistical model to find the internal structure of comet-sized planetesimals. In this paper we develop a numerical model that keep track of at what depth particles inside the pebble cloud are to get the radial structure of the resulting planetesimal. We find that the interiors of a planetesimal is heavily dependent on initial pebble sizes and depth inside the planetesimal. We also look at what effect disc gas has on the collapse by adding gas drag onto particles. This both speeds up the collapse and cause lower collision speeds which results in primordial pebbles surviving the collapse. The dependence on particle sizes result in planetesimals with an interior of “onion”-like shells. Our results are in agreement with Rosetta observations of 67P/Churyumov–Gerasimenko being a porous, homogeneous pebble-pile. (Less)