First synthesis of tepidopterin [2'-O-(2-acetamido-2-deoxy-beta-d-glucopyranosyl)-L-threo-biopterin

N(2)-(N,N-Dimethylaminomethylene)-1'-O-(4-methoxybenzyl)-3-[2-(4-nitrophenyl)ethyl]-L-threo-biopterin (14) was prepared from L-xylose in an 11-step-sequence. The first synthesis of tepidopterin (3) was achieved by treatment of 14 with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl bromide in the presence of silver triflate and tetramethylurea, followed by removal of the protecting groups.     

Specific Features of Phase Transfer Catalytic Glycosylation of 2-Mercaptobenzimidazole

Russian Journal of Bioorganic Chemistry - The reaction of 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl chloride with 2?mercaptobenzimidazole under conditions of the phase...     

Synthesis of N4-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine analogues: succinamide, L-2-hydroxysuccinamide, and L-2-hydroxysuccinamic acid hydrazide analogues

The syntheses of three analogues of N4-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine are described. N-(2-Acetamido-2-deoxy-beta-D-glucopyranosyl)succinamide was synthesized by the reaction of pentafluorophenyl succinamate with 2-acetamido-2-deoxy-beta-D-glucopyranosylamine. 2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosylamine was synthesized, and the complete assignment of the 1H NMR spectrum is given. Reaction of the protected beta-D-glycosylamine with L-malic acid chloralid in the presence of a coupling agent (EEDQ) gave N4-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-L-malamic acid chloralid that was deprotected two ways: (1) using ammonia, which gave N4-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-2-hydroxysuccinamide, and (2) using hydrazine, which gave N4-(2-acetamido-2-deoxy-1-D-glucopyranosyl)-L-2-hydroxysuccinamic acid hydrazide.     

Access to tetrachlorophthalimide-protected ethyl 2-amino-2-deoxy-1-thio-beta-D-glucopyranosides.

Ethyl 2-deoxy-2-tetrachlorophthalimido-1-thio-beta-D-glucopyranoside (7) was prepared from glucosamine hydrochloride in four steps with a 20-25% overall yield. Formation of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-tetrachlorophthalimido-beta-D- glucopyranoside (5) was found to be crucial for this reaction sequence since the corresponding alpha-1-acetate did not react in Lewis-acid-catalyzed ethylthio glycosidations. Formation of the beta-1-acetate (5) was achieved by treatment of 3,4,6-tri-O-acetyl-2-deoxy-2-tetrachlorophthalimido-alpha-D-glucop yranosyl bromide (4) with acetic acid under silver zeolite promotion. This was necessary because conditions normally used for beta-1-acetate formation were not tolerated by the tetrachlorophthalimido (TCP) group.     

A convenient synthetic route to the disaccharide repeating-unit of peptidoglycan

Glycosylation of the readily accessible benzyl 2-acetamido-6-O-benzyl-2-deoxy-3-O-[(R)-1-(methoxycarbonyl)ethyl]-alpha- D- glucopyranoside with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl chloride (2), using the silver triflate method in the absence of a base, afforded 65-70% of the fully protected [beta-D-GlcNPhth-(1----4)-MurNAc] methyl ester derivative 4, the structure of which was ascertained on the basis of 500-MHz 1H-n.m.r. data. 2,2'-Dideoxy-2,2'-diphthalimido-beta,beta-trehalose hexa-acetate was a by-product. Removal of the Phth group from 4, followed by acetylation, yielded 90% of the acetylated 1,6-di-O-benzyl derivative 5, which, on saponification and catalytic hydrogenation, afforded 2-acetamido-4-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-3-O-[(R)-1- carboxyethyl]-2-deoxy-D-glucopyranose. Similarly, 5 was converted into the acetylated methyl ester derivative, which, on selective removal of the methyl ester group, gave benzyl 2-acetamido-4-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D- glucopyranosyl)-6-O-benzyl-3-O-[(R)-1-carboxyethyl]-2-deoxy-alpha-D- glucopyranoside. An alternative route for the preparation of 2 is described.     

Synthesis and biological activity of some lipophilic derivatives of 1-thio-muramoyl-L-alanyl-D-isoglutamine

2-N-Octadecanoyl derivatives of 1-S-acetyl-, 1-S-octadecanoyl-, and of 6-O-octadecanoyl-1-S-octadecanoyl-1-thiomuramoyl-L-ala nyl-D-isoglutamine were synthesized from benzyl 3,4,6-tri-O-acetyl-2-deoxy-2-(octadecanoylamino)-beta-D-glucopy ran oside. Their immunoadjuvant activities were examined in guinea-pigs.     

Synthesis of three disaccharides for the preparation of immunogens bearing immunodeterminants known to occur on glycoproteins

p-Nitrophenyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside was condensed with 2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl bromide, the product deprotected, and the disaccharide glycoside converted into p-trifluoroacetamidophenyl 2-acetamido-2-deoxy-4-O-beta-D-galactopyranosyl-beta- D-glucopyranoside. p-Nitrophenyl 3-O-benzoyl-4,6-di-O-benzylidene-alpha-D-mannopyranoside was condensed with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl bromide, and the product was deprotected, to yield p-nitrophenyl 2-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-alpha-D-mannopyranoside. p-Nitrophenyl 2-acetamido-3,4-di-O-benzoyl-2-deoxy-beta-D-glucopyranoside was condensed with 2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl bromide, and, after reduction, trifluoroacetylation, and deprotection, p-trifluoroacetamidophenyl 2-acetamido-2-deoxy-6-O-alpha-L-fucopyranosyl-beta-D-glucopyranoside was obtained.     

Syntheses of T(N) building blocks Nalpha-(9-fluorenylmethoxycarbonyl)-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-galactopyranosyl)-L-serine/L-threonine pentafluorophenyl esters: comparison of protocols and elucidation of side reactions

T(N) antigen building blocks Nalpha-(9-fluorenylmethoxycarbonyl)-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-galactopyranosyl)-L-serine/L-threonine pentafluorophenyl ester [Fmoc-L-Ser/L-Thr(Ac3-alpha-D-GalN3)-OPfp, 13/14] have been synthesized by two different routes, which have been compared. Overall isolated yields [three or four chemical steps, and minimal intermediary purification steps] of enantiopure 13 and 14 were 5-18% and 6-10%, respectively, based on 3,4,6-tri-O-acetyl-D-galactal (1). A byproduct of the initial azidonitration reaction of the synthetic sequence, that is, N-acetyl-3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-galactopyranosylamine (5), has been characterized by X-ray crystallography, and shown by 1H NMR spectroscopy to form complexes with lithium bromide, lithium iodide, or sodium iodide in acetonitrile-d3. Intermediates 3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-galactopyranosyl bromide (6) and 3,4,6-tri-O-acetyl-2-azido-2-deoxy-beta-D-galactopyranosyl chloride (7) were used to glycosylate Nalpha-(9-fluorenylmethoxycarbonyl)-L-serine/L-threonine pentafluorophenyl esters [Fmoc-L-Ser/L-Thr-OPfp, 11/12]. Previously undescribed low-level dehydration side reactions were observed at this stage; the unwanted byproducts were easily removed by column chromatography.     

Unexpected stereochemical outcome of activated 4,6-O-benzylidene derivatives of the 2-deoxy-2-trichloroacetamido-D-galacto series in glycosylation reactions during the synthesis of a chondroitin 6-sulfate trisaccharide methyl glycoside

The synthesis of methyl (beta-D-glucopyranosyluronic acid)-(1-->3)-(2-acetamido-2-deoxy-6-O-sulfonato-beta-D-galactopyr anosyl)-(1-->4)-(beta-D-glucopyranosid)uronate trisodium salt, a chondroitin 6-sulfate trisaccharide derivative, is described. Loss of stereocontrol in glycosylation reactions involving activated 4,6-O-benzylidene derivatives of the 2-deoxy-2-trichloroacetamido-D-galacto series and D-glucuronic acid-derived acceptors was highlighted. This draw-back was overcome through the use of phenyl 3,4,6-tri-O-acetyl-2-deoxy-1-thio-2-trichloroacetamido-beta-D-gala ctopyranoside, which afforded the desired beta-linked disaccharide derivative in high yield with an excellent stereoselectivity. This later was submitted to acid-catalyzed methanolysis, followed by benzylidenation, and condensed with methyl 2,3,4-tri-O-benzoyl-1-O-trichloroacetimidoyl-alpha-D-glucopyran uronate to afford the expected trisaccharide derivative. Subsequent transformation of the N-trichloroacetyl group into N-acetyl, mild acid hydrolysis, selective O-sulfonation at C-6 of the amino sugar moiety, and saponification afforded the target molecule as its sodium salt in high yield.     

Two-step regio- and stereoselective syntheses of [19F]- and [18F]-2-deoxy-2-(R)-fluoro-beta-D-allose

Replacement of specific hydroxyl groups by fluorine in carbohydrates is an ongoing challenge from chemical, biological, and pharmaceutical points of view. A rapid and efficient two-step, regio- and stereoselective synthesis of 2-deoxy-2-(R)-fluoro-beta-d-allose (2-(R)-fluoro-2-deoxy-beta-d-allose; 2-FDbetaA), a fluorinated analogue of the rare sugar, d-allose, is described. TAG (3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-d-arabino-hex-1-enitol or 3,4,6-tri-O-acetyl-d-glucal), was fluorinated in anhydrous HF with dilute F(2) in a Ne/He mixture or with CH(3)COOF at -60 degrees C. The fluorinated intermediate was hydrolyzed in 1N HCl and the hydrolysis product was purified by liquid chromatography and characterized by 1D (1)H, (13)C, and (19)F NMR spectroscopy as well as 2D NMR spectroscopy and mass spectrometry. In addition, (18)F-labeled 2-deoxy-2-(R)-fluoro-beta-d-allose (2-[(18)F]FDbetaA) was synthesized for the first time, with an overall decay-corrected radiochemical yield of 33+/-3% with respect to [(18)F]F(2), the highest radiochemical yield achieved to date for electrophilic fluorination of TAG. The rapid and high radiochemical yield synthesis of 2-[(18)F]FDbetaA has potential as a probe for the bioactivity of d-allose.     

Synthesis of a peripheral trisaccharide sequence of lutropin, a pituitary glycoprotein hormone; use of chitobiose as a key starting material

A chitobiose derivative, methyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1--- -4)-3,6 - di-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside, was derived from the corresponding N-acetyl derivative and this was converted into the glycosyl bromide (5). Glycosidation reaction between 5 and methyl 3,4,6-tri-O-benzyl-alpha-D-mannopyranoside in the presence of silver trifluoromethanesulfonate gave a beta-D-linked trisaccharide derivative. Replacement of the N,N-phthaloyl group by acetyl groups resulted in a product that was converted into methyl O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosyl)-(1----4)-O -(2- acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosyl)-(1----2)-3,4,6- tri-O- benzyl-alpha-D-mannopyranoside (11) by use of a few reaction steps. The 4(3)-hydroxyl group of 11 was methanesulfonylated, and the product subjected to SN2 replacement with acetate anion, to give the D-galactosamine-containing trisaccharide derivative (12). After basic hydrolysis of 12, the 4(3)-hydroxyl group was sulfated, and all benzyl groups were removed by hydrogenolysis, giving methyl O-(2-acetamido-2-deoxy-4-O-sulfo-beta-D-galactopyranosyl)-(1----4)-O-(2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----2)-alpha-D-mannopyranosid e monosodium salt, the methyl alpha-glycoside derivative of the peripheral trisaccharide sequence of the pituitary glycoprotein hormone lutropin.     

Synthesis and evaluation of a radioiodinated trisaccharide derivative as a synthetic substrate for a sensitive N-acetylglucosaminyltransferase V radioassay

N-acetylglucosaminyltransferase V (GnT-V) is one of the most relevant glycosyltransferases to tumor invasion and metastasis. Based on previous findings of molecular recognition between GnT-V and synthetic substrates, we designed and synthesized a p-iodophenyl-derivatized trisaccharide, 2-(4-iodophenyl)ethyl 6-O-[2-O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-α-d-mannopyranosyl]-β-D-glucopyranoside (IPGMG, 1) and its radiolabeled form, [(125)I]IPGMG ([(125)I]1), for use in assays of GnT-V activity in vitro. The tributyltin derivative, 2-[4-(n-tributylstannyl)phenyl]ethyl 6-O-[2-O-(3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranosyl)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl]-2,3,4-tri-O-acetyl-β-D-glucopyranoside (21), was synthesized as a precursor for the preparation of [(125)I]1. The iododestannylation of 21 using hydrogen peroxide as an oxidant followed by deacetylation yielded [(125)I]1. When [(125)I]1 was incubated in GnT-V-expressing cells with a UDP-GlcNAc donor, the production of β1-6GlcNAc-bearing IPGMG (IPGGMG, 2) was confirmed by radio-HPLC. In kinetic analysis, 1 was found to be a good substrate with a K(m) of 23.7 μM and a V(max) of 159 pmol/h. μg protein. [(125)I]1 would therefore be a useful synthetic substrate for the quantitative determination of GnT-V activity.     

Rearrangement of unsaturated 2,4-O-benzylidenehexitol derivatives into C-glycosylbenzene derivatives.

Acetolysis of (Z)-1,3-di-O-acetyl-2,4-O-benzylidene-6-C-(2,4-dichlorophenyl)-D-xylo-he x- 5-enitol (3) afforded (E)-1,2,3,4-tetra-O-acetyl-6-C-(2,4-dichlorophenyl)-D-xylo-hex-5-enit ol and 2-C-[(R)-acetoxy(2,4-dichlorophenyl)methyl]-3,4,6-tri-O-acetyl-2-deoxy- beta-L-galacto- and -beta-L-gulo-hexopyranosylbenzene. The mechanism of this new rearrangement was studied by exchanging the substituents at C-1 and C-3 in 3 and those of the aromatic ring attached to C-6.     

Synthesis and solid state 13C and 1H NMR analysis of new oxamide derivatives of methyl 2-amino-2-deoxy-alpha-D-glucopyranoside and ester of amino acids or dipeptides

The syntheses of new oxamide derivatives of methyl 2-amino-2-deoxy-alpha-D-glucopyranoside and amino acid or peptide esters are presented. The reaction of methyl 3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-alpha-D-glucopyranoside and oxalyl chloride gave N-(methyl 3,4,6-tri-O-acetyl-2-deoxy-alpha-D-glucopyranosid-2-yl) oxamic acid chloride which on reaction with the ester of Gly, L-Ala, L-Phe, GlyGly, Gly-L-Phe and Gly-L-Ala afforded N-(methyl 3,4,6-tri-O-acetyl-2-deoxy-alpha-D-glucopyranosid-2-yl), N'-oxalyl-amino acid or dipeptide esters. The structure of the oxamides was studied using 1H, 13C NMR in solution and solid state.     

Synthesis of the pentasaccharide repeating unit of lactosillan [correction of latosillan

A pentasaccharide, beta-D-Man-(1-->2)-[beta-D-GlcNAc-(1-->4)]-alpha-L-Rha-(1-->4)-alpha-L-Rha-(1-->4)-alpha-L-Rha-1-OC8H17, representing the repeating unit of latosillan, was convergently synthesized from the building blocks, ethyl 2,3-O-isopropylidene-1-thio-alpha-l-rhamnopyranoside, 2-O-acetyl-3,4,6-tri-O-benzyl-beta-d-glucopyranosyl trichloroacetimidate, and 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-d-glucopyranosyl trichloroacetimidate under standard glycosylation conditions. The target pentasaccharide showed acceptable differentiation-inducing activity on HL-60 cell lines at the dosages of 10-50 microg/mL.     

Syntheses of neoglycolipids with hexitol spacers between the saccharidic and the lipidic parts

Four neoglycolipids having 2-amino-2-deoxy-D-glucose or D-galactose moieties linked to the lipidic part by a glucitol or a mannitol spacer-arm have been synthesized. The key step of the synthetic strategy was the regiospecific or regioselective beta-glycosylation of partially protected glucitol or mannitol acceptors by either 3,4,6-tri-O-acetyl-2-deoxy-2-iodo-alpha-D-mannopyranosyl azide or 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate donors.     

Synthesis of S-linked thiooligosaccharide analogues of Nod factors: synthesis of new protected thiodisaccharide and thiotrisaccharide intermediates

We are investigating the synthesis of thioanalogues of nodulation factors that will be resistant to degradation by chitinases. To study the influence of our protecting group strategy, the glycosylation of 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-beta-D-glucopyranoside (7) with two trichloroacetimidate glycosyl donors carrying an azido group at C-2 and either benzyl or benzoyl protecting groups on O-3 and O-4 was first attempted under catalysis with BF(3).Et(2)O in toluene. While glycosylation with the benzoylated glycosyl donor gave only a poor yield (27%) of the disaccharide, a similar reaction with the benzylated donor gave the corresponding disaccharide in good yield (77%). Although both products were obtained as anomeric mixtures, the benzylated donor led to improved stereoselectivity in favor of the desired beta-anomer (alpha:beta 3:7). Based on these results, a novel thiotrisaccharide was synthesized via the coupling of 7 with 6-O-acetyl-4-S-(3,4,6-tri-O-acetyl-2-benzyloxycarbonylamino-2-deoxy-beta-D-glucopyranosyl)-2-azido-3-O-benzyl-2-deoxy-4-thio-alpha-D-glucopyranosyl trichloroacetimidate (25) also newly synthesized. After optimization of the reaction conditions, the desired thiotrisaccharide 4-O-[6-O-acetyl-4-S-(3,4,6-tri-O-acetyl-2-benzyloxycarbonylamino-2-deoxy-beta-D-glucopyranosyl)-2-azido-3-O-benzyl-2-deoxy-4-thio-beta-D-glucopyranosyl]-1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-beta-D-glucopyranoside (26beta) was obtained in 57% yield. These conditions led to an anomeric mixture in favor of the desired beta-anomer (alpha:beta 1:4.7) that was separated from the alpha-anomer by normal-phase HPLC on a PrepNova Pack(R) silica gel cartridge. The work described here shows that thiodisaccharide glycosyl donors behave quite differently from the analogous O-disaccharide used previously to synthesize nodulation factors.     

Synthesis and glycan priming activity of acetylated disaccharides

Five disaccharides related in structure to the glycans of vertebrate mucins have been chemically synthesized using orthogonal blocking, coupling and deblocking techniques. These include 2-naphthylmethyl 3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl-( 1 --> 4)-2-acetamido-3,6-di-O-acetyl-2-deoxy-beta-D-glucopyranoside (6), 2-naphthylmethyl 2-aceta-mido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl-(1 --> 3)-2,4,6-tri-O-acetyl-beta-D-galactopyranoside (14), 2-naph-thylmethyl2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl-(1 --> 3)-2-acetamido-4,6-di- O-acetyl-2-deoxy-alpha-D-galactopyranoside (20), 2-naphthylmethyl 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl-(1 --> 3)-2-acetamido-4,6-di-O-acetyl-2-deoxy-alpha-D-galactopyranoside (23) and 2-naphthylmethyl 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glu-copyranosyl-(1 --> 6)-2-acetamido-3,4-di-O-acetyl-2-deoxy-alpha-D-galactopyranoside (27). These per-O-acetylated compounds were fed to U-937 cells to test their ability to prime oligosaccharide synthesis, inhibit glycoprotein biosynthesis and alter adhesion to E-selectin expressed on endothelial cells. The results show that 6, 14, and 20 served as substrates for oligosaccharide synthesis. The generation of glycoside-primed glycans altered the formation of glycoproteins on the cell surface and inhibited cell adhesion dependent on E-selectin.     

A highly concise preparation of O-deacetylated arylthioglycosides of N-acetyl-D-glucosamine from 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-alpha-D-glucopyranosyl chloride and aryl thiols or disulfides

An expedient and mild route to a range of aryl 2-acetamido-2-deoxy-1-thio-beta-D-glucopyranosides has been devised from 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-alpha-D-glucopyranosyl chloride and arylthiols or aryl disulfides using phase transfer catalysis conditions. This simple procedure compresses up to three synthetic steps into a one-pot reaction, obviating the need for tedious workups and chromatography and directly furnishes crystalline materials in good yields. The procedure is compatible with a range of thiols and disulfides and may be amenable for preparing a wide range of thioglycosides with various glycons and aglycons.     

Synthesis of beta-D-GlcpNAc-(1-->3)-alpha-L-Rhap-(1-->2)-[beta-L-Xylp-(1-->4)]-alpha-L-Rhap-(1-->3)-alpha-L-Rhap,the repeating unit of the O-antigen produced by Pseudomonas solanacearum ICMP 7942

An efficient synthesis of beta-D-GlcpNAc-(1-->3)-alpha-L-Rhap-(1-->2)-[beta-L-Xylp-(1-->4)]-alpha-L-Rhap-(1-->3)-alpha-L-Rhap, the repeating unit of the O-antigen produced by Pseudomonas solanacearum ICMP 7942 and its isomer beta-D-GlcpNAc-(1-->3)-alpha-L-Rhap-(1-->4)-[beta-L-Xylp-(1-->2)]-alpha-L-Rhap-(1-->3)-alpha-L-Rhap was achieved via sequential assembly of the building blocks, allyl 2,3-O-isopropylidene-alpha-L-rhamnopyranoside (2), allyl 3,4-O-isopropylidene-alpha-L-rhamnopyranoside (3), allyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside (6), 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl trichloroacetimidate (7), and 2,3,4-tri-O-benzoyl-beta-L-xylopyranosyl trichloroacetimidate (12). The process was carried out in a regio- and stereoselective manner using glycosyl trichloroacetimidates as donors and unprotected or partially protected rhamnopyranosides as acceptors in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf).