Efficient synthesis of methyl lycotetraoside, the tetrasaccharide constituent of the tomato defence glycoalkaloid alpha-tomatine

Branched oligosaccharide lycotetraose, beta-D-glucopyranosyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3)]-beta-D-glucopyranosyl-(1-->4)-beta-D-galactopyranose, is a key constituent of many steroidal saponins, including glycoalkaloid alpha-tomatine, which is involved in protection of plants from invading pathogens. A new synthesis of the methyl beta-lycotetraoside () is described. Key steps of the synthesis include two successive glycosylation reactions of disaccharide acceptor methyl (4,6-O-benzylidene-3-O-p-methoxybenzyl-beta-D-glucopyranosyl)-(1-->4)-2,3,6-tri-O-benzyl-beta-D-galactopyranoside with readily available benzoylated trichloroacetimidates of alpha-D-glucopyranose and alpha,beta-D-xylopyranose. This scheme allows sequential glycosylation in one-pot on account of the convenient in situ removal of a p-methoxybenzyl protecting group under the acid conditions of the first glycosylation step. Following deprotection, tetrasaccharide was obtained in 19% yield over eight steps.     

Total synthesis of quercetin 3-sophorotrioside

5,7-dihydroxy-3-[beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl]-2-(3,4-dihydroxyphenyl)-4H-1-benzopyran-4-one (quercetin 3-sophorotrioside), a flavonol triglycoside, isolated from Pisum sativum shoots and showing protective effects on liver injury induced by chemicals, was synthesized for the first time. The target compound was successfully synthesized in eight linear steps and in 39% overall yield through a combination of phase-transfer-catalyzed (PTC) quercetin C-3 glycosylation and silver triflate (AgOTf) promoted carbohydrate chain elongation using both sugar bromide and trichloroacetimidate donors.     

Synthesis of an antimetastatic tetrasaccharide β-D-Gal-(1→4)-β-d-GlcpNAc-(1→6)-α-D-Manp-(1→6)-β-D-Manp-OMe

An antimetastatic tetrasaccharide T₁,β-D-Gal-（1→4）-β-D-GlcpNAc-（1→6）-α-D-Manp-（1→6）-β-D-Manp-OMe,was synthesized with two approaches.The first approach was a conventional method employing thioglycoside and Koenigs-Knorr glycosylation reaction in 24%overall yield.The second one was a novel route through the azidoiodo-glycosylation strategy by using 2-iodo-2-deoxylactosyl azide as the donor in 36%overall yield.     

Stereoselective tris-glycosylation to introduce beta-(1-->3)-branches into gentiotetraose for the concise synthesis of phytoalexin-elicitor heptaglucoside

Dodecyl thioglycosides (3, 4, 5) were prepared by conventional transformation of d-glucose and used as new glycosyl donors for a short-step synthesis of phytoalexin elicitor heptaglucoside. A gentio-tetraoside derivative (6) having three hydroxyl groups was synthesized by NIS-TfOH promoted glycosylate in more than 90% yield followed by selective removal of temporary protective groups. Undesired formation of alpha-glycosides at the introduction of beta-(1-->3)-branches into gentio-oligosaccharides was found to be suppressed by use of a thiophilic reagent system, BSP (1-benzenesulfinyl piperidine)-Tf2O, giving the heptaglucoside in only four glycosylation steps.     

Halogenated 7-deazapurine nucleosides: stereoselective synthesis and conformation of 2'-deoxy-2'-fluoro-beta-D-arabinonucleosides

The stereoselective syntheses of 5-halogenated 7-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine nucleosides 3b-d, 4a-c as well as 7-deaza-2'-deoxyisoguanosine are described. Nucleobase anion glycosylation of 2-amino-4-chloro-7H-pyrrolo[2,3-d]pyrimidine (5) with 3,5-di-O-benzoyl-2-deoxy-2-fluoro-alpha-D-arabinofuranosyl bromide (6) exclusively gave the beta-D-anomer, which was deblocked (--> 8), aminated at C4 (--> 3a) and selectively deaminated at C2 to yield 2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl 7-deazaisoguanine (2). Condensation of the 5-halogenated 4-chloro-2-pivaloylamino-7H-pyrrolo[2,3-d]pyrimidines 9a-c with 6 furnished the N7-nucleosides 10a-c together with N2,N7-bisglycosylated compounds 11a-c. The former was converted to the corresponding 2,4-diamino-compounds 3b-d, and the latter was deblocked by NaOMe/MeOH to yield the 4-methoxy-nucleosides 4a-c. Conformational analysis of the sugar moiety of the nucleosides 2 and 3a-d was performed on the basis of vicinal [1H,1H] coupling constants. The fluorine atom in the sugar moiety shifts the sugar conformation from S towards N by about 10%, while the halogen substituents in the base moiety increase the hydrophobicity and polarizability of the nucleobases.     

Transsialidase from Trypanosoma cruzi for regio- and stereoselective synthesis of N-acyl-modified sialylated oligosaccharides and measurement of transfer rates

Recombinant transsialidase from Trypanosoma cruzi (TcTS) was used for the sialylation with natural and non-natural derivatives of neuraminic acid. Neu5Ac-alpha(2-->3)-Gal-beta(1-->6)-Glc-alphaOMe was prepared in 80 % yield. Correspondingly, the modified trisaccharide derivatives Neu5Prop-alpha(2-->3)-Gal-beta(1-->6)-Glc-alphaOMe (32 %) and Neu5Gc-alpha(2-->3)-Gal-beta(1-->6)-Glc-alphaOMe (Prop=propanoyl, Gc=glycolyl) were obtained in 60 % yield, respectively.     

Direct chemical synthesis of the beta-D-mannans: the beta-(1-->2) and beta-(1-->4) series

The direct syntheses of a beta-(1-->2)-mannooctaose and of a beta-(1-->4)-mannohexaose are reported by means of 4,6-O-benzylidene-protected beta-mannosyl donors. The synthesis of the (1-->2)-mannan was achieved by means of the sulfoxide coupling protocol, whereas the (1-->4)-mannan was prepared using the analogous thioglycoside/sulfinamide methodology. In the synthesis of the (1-->4)-mannan, the glycosylation yields and stereoselectivities remain approximately constant with increasing chain length, whereas those for the (1-->2)-mannan consist of two groups with the formation of the tetra- and higher saccharides giving yields and selectivities consistently lower than those of the lower homologues. The decrease in yield after the trisaccharide in the (1-->2)-mannan synthesis is attributed to steric interference by the n-3 residue and is consistent with the collapsed, disordered structure predicted by early computational work. The consistently high yields and selectivities seen in the synthesis of the (1-->4)-mannan are congruent with the more open, ordered structure originally predicted for this polymer. The lack of order in the structure of the (1-->2)-mannan, as compared to the high degree of order in the (1-->4)-mannan, is also evident from a comparison of the NMR spectra of the two polymers and even from their physical nature: the (1-->2)-mannan is a gum and the (1-->4)-mannan is a high melting solid.     

Preparation of a chiral synthon for an HBV inhibitor: enzymatic asymmetric hydrolysis of (1α,2β,3α)-2-(benzyloxymethyl)cyclopent-4-ene-1,3-diol diacetate and enzymatic asymmetric acetylation of (1α,2β,3α)-2-(benzyloxymethyl)cyclopent-4-ene-1,3-diol

Enantioselective asymmetric hydrolysis of (1α,2β,3α)-2-(benzyloxymethyl)-cyclopent-4-ene-1,3-diol diacetate 1 to the corresponding (+)-monoacetate 2 was carried out using lipase PS-30 from Pseudomonas cepacia or pancreatin. A reaction yield of 85 M % with an enantiomeric excess (ee) of 98% was obtained. Using pancreatin, a reaction yield of 75 M % with an ee of 98.5% was obtained. Asymmetric acetylation of (1α,2β,3α)-2-(benzyloxymethyl)-cyclopent-4-ene-1,3-diol 3 to the corresponding (−)-monoacetate 4 was carried out using lipase PS-30 with isopropenyl acetate as the acylating agent. A reaction yield of 80 M % with an ee of 98% was obtained for (−)-monoacetate 4.     

Synthesis of spirostanol saponins via gold(I)‐catalyzed glycosylation in the presence of Ga(OTf)3, In(OTf)3, or HOTf

An effective approach relying on a Lewis acid‐ or Brønsted acid‐assisted gold(I)‐catalyzed glycosylation has been reported in the synthesis of a panel of the representative natural spirostanol saponins, namely polyphyllin D ( 1 ), polyphyllin V ( 2 ), dioscin ( 3 ), formosanin C ( 4 ), and a derivative of polyphyllin D bearing a terminal azide group ( 5 ). This approach highlights the engagement of low loadings of Ph₃AuPOTf (≤ 0.5 mol%) in the presence of Ga(OTf)₃, In(OTf)₃, or HOTf (~10mol%) as a co‐catalyst, at practical reaction rates as an alternative to the conventional ~10 mol% loadings of the gold(I) catalyst in the glycosylation. Polyphyllin D ( 1 ) was obtained in 41% overall yield over six steps compared to the maximum 30% yield in previous syntheses where conventional donors and promoters were used. By exploiting a regioselective rhamnosylation, a “one‐pot” approach was adopted to assemble 1 and 5 , thus further strengthening the efficiency of the gold(I)‐catalyzed glycosylation.     

The 2-naphthylmethyl (NAP) group in carbohydrate synthesis: first total synthesis of the GlyCAM-1 oligosaccharide structures

Total syntheses of the GlyCAM-1 (glycosylation-dependent cell adhesion molecule-1) oligosaccharide structures: [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-(6-O-SO3Na)-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (1) and [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (2) through a novel sialyl LewisX tetrasaccharide donor are described. Employing sequential glycosylation strategy, the starting trisaccharide was regio- and stereoselectively constructed through coupling of a disaccharide imidate with the monosaccharide acceptor phenyl-6-O-naphthylmethyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside with TMSOTf as a catalyst without affecting the SPh group. The novel sialyl Lewisx tetrasaccharide donor 3 was then obtained by alpha-L-fucosylation of trisaccharide acceptor with the 2,3,4-tri-O-benzyl-1-thio-beta-L-fucoside donor. The structure of the novel sialyl Lewisx tetrasaccharide was established by a combination of 2D DQF-COSY and 2D ROESY experiments. Target oligosaccharides 1 and 2 were eventually constructed through heptasaccharide which was obtained by regioselective assembly of advanced sialyl Lewisx tetrasaccharide donor 3 and a sialylated trisaccharide acceptor in a predictable and controlled manner. Finally, target heptasaccharides 1 and 2 were fully characterized by 2D DQF-COSY, 2D ROESY, HSQC, HMBC experiments and FAB mass spectroscopy.     

Synthesis of the (1S,2S)- and (1R,2S)-stereoisomers of the respective E- and Z-isomers of ethyl 4-[(2-hydroxycyclohexyl)methyl]phenoxy-3-methyl-2-butenoate using yeast whole cell bioreduction of the parent ketones

Saccharomyces cerevisiae, strain DBM 2115, was successfully employed in the reduction of the separated Z- and E-isomers of ethyl 4-[(2-oxocyclohexyl)methyl]phenoxy-3-methyl-2-butenoates 1 and 2, in order to prepare the (1S,2S)- and (1R,2S)-enantiomers of the corresponding ethyl 4-[(2-hydroxycyclohexyl)methyl]phenoxy-3-methyl-2-butenoates 3–6. The products were obtained with the required absolute configuration: (1S,2S)-3 (ee = 98%; yield 48%), (1R,2S)-4 (ee = >99%; yield 45%), (1S,2S)-5 (ee = 98.5%; yield 47%), and (1R,2S)-6 (ee = >99%; chemical yield 44%).     

1,N6-Etheno-7-deaza-2,8-diazaadenosine: syntheses, properties and conversion to 7-deaza-2,8-diazaadenosine

1,N6-Etheno-7-deaza-2,8-diazaadenosine (4) was synthesized from 8-aza-7-deazaadenosine (6) in 64% overall yield. The starting material 6 was obtained by the direct glycosylation of 8-aza-7-deazaadenine (7) with 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-d-ribofuranose (8) (NO2 CH3, BF3 x Et2O; 77% yield). Compound 4 was transformed into 7-deaza-2,8-diazaadenosine (5). The fluorescence of compound 4 shows an emission maximum at 531 nm (phosphate buffer; pH 7.0), which is bathochromically shifted compared to 1,N(6)-etheno-2-azaadenosine (3a) (495 nm). A conformational analysis was performed in the solid state and in solution.     

Development of an enantioselective synthetic route to neocarzinostatin chromophore and its use for multiple radioisotopic incorporation

A convergent, enantioselective synthetic route to the natural product neocarzinostatin chromophore (1) is described. Synthesis of the chromophore aglycon (2) was targeted initially. Chemistry previously developed for the synthesis of a neocarzinostatin core model (4) failed in the requisite 1,3-transposition of an allylic silyl ether when applied toward the preparation of 2 with use of the more highly oxygenated substrates 27 and 54. An alternative synthetic plan was therefore developed, based upon a proposed reduction of the epoxy alcohol 58 to form the aglycon 2, a transformation that was achieved in a novel manner, using a combination of the reagents triphenylphosphine, iodine, and imidazole. The successful route to 1 and 2 began with the convergent coupling of the epoxydiyne 15, obtained in 9 steps (43% overall yield) from D-glyceraldehyde acetonide, and the cyclopentenone (+)-14, prepared in one step (75-85% yield) from the prostaglandin intermediate (+)-16, affording the alcohol 22 in 80% yield and with > or =20:1 diastereoselectivity. The alcohol 22 was then converted into the epoxy alcohol 58 in 17 steps with an average yield of 92% and an overall yield of 22%. Key features of this sequence include the diastereoselective Sharpless asymmetric epoxidation of allylic alcohol 81 (98% yield); intramolecular acetylide addition within the epoxy aldehyde 82, using Masamune's lithium diphenyltetramethyldisilazide base (85% yield); selective esterification of the diol 84 with the naphthoic acid 13 followed by selective cleavage of the chloroacetate protective group in situ to furnish the naphthoic acid ester 85 in 80% yield; and elimination of the tertiary hydroxyl group within intermediate 88 using the Martin sulfurane reagent (79% yield). Reductive transposition of the product epoxy alcohol (58) then formed neocarzinostatin chromophore aglycon (2, 71% yield). Studies directed toward the glycosylation of 2 focused initially on the preparation of the N-methylamino --> hydroxyl replacement analogue 3, an alpha-D-fucose derivative of neocarzinostatin chromophore, formed in 42% yield by a two-step Schmidt glycosylation-deprotection sequence. For the synthesis of 1, an extensive search for a suitable 2'-N-methylfucosamine glycosyl donor led to the discovery that the reaction of 2 with the trichloroacetimidate 108, containing a free N-methylamino group, formed the alpha-glycoside 114 selectively in the presence of boron trifluoride diethyl etherate. Subsequent deprotection of 114 under mildly acidic conditions then furnished the labile chromophore (1). The synthetic route was readily modified for the preparation of singly and doubly (3)H- and (14)C-labeled 1, compounds unavailable by other means, for studies of the mechanism of action of neocarzinostatin in vivo.     

Synthesis of the glycopeptidolipid of Mycobacterium avium Serovar 4: first example of a fully synthetic C-mycoside GPL

The preparation of the glycopeptidolipid (GPL) present in the cell wall of Mycobacterium aviumSerovar 4, namely 3,4-di-O-Me-alpha-L-Rhap-(1-->1)[R-C(21)H(43)CH(OH)CH(2)CO-D-Phe-[4-O-Me-alpha-L-Rhap-(1-->4)-2-O-Me-alpha-L-Fucp-(1-->3)-alpha-L-Rhap-(1-->2)-6-deoxy-alpha-L-Talp-(1-->3)]-D-allo-Thr-D-Ala-L-Alaol] (1), is described. The synthesis was based on the disconnection of the final structure into four building blocks, an L-rhamnosyl pseudodipeptide, a 6-deoxy-L-talosyl dipeptide, a trisaccharide donor, and a 3-hydroxyalkanoic acid. The key steps are the creation of the glycosidic linkage between the trisaccharide donor, used as a pentenyl glycoside, and the 6-deoxy-L-talose unit of an appropriate D-Phe-O-(6-deoxy-L-talosyl)-D-allo-Thr derivative and the final coupling of the two glycodipeptide fragments. Pentenyl glycosides were shown to provide useful donors in several glycosylation steps. This work constitutes the first synthesis of the full structure of a so-called "polar mycoside C" GPL.     

Synthesis of a Single Repeat Unit of Type VIII Group B Streptococcus Capsular Polysaccharide 1

Abstract

We have synthesized a single repeat unit of type VIII Group B Streptococcus capsular polysaccharide, the structure of which is {L-Rhap(β1→4)-D-Glcp(β1→4)[Neu5Ac(α2→3)]-D-Galp(β→4)}_n. The synthesis presented three significant synthetic challenges namely: the L-Rhap(β→4)-D-Glcp bond, the Neu5Ac(α2→3)-D-Galp bond and 3,4-D-Galp branching. The L-Rhap bond was constructed in 60% yield (α:β 1:1.2) using 4-O-acetyl-2,3-di-O-benzoyl-α-L-rhamnopyranosyl bromide 6 as donor, silver silicate as promotor and 6-O-benzyl-2,3-di-O-benzoyl-1-thio-β-D-glucopyranoside as acceptor to yield disaccharide 18. The Neu5Ac(α2→3) linkage was synthesized in 66% yield using methyl [phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-D-galacto-nonulopyranosid]onate as donor and triol 2-(trimethylsilyl) ethyl 6-O-benzyl-β-D-galactopyranoside as acceptor to give disaccharide 21. The 3,4-D-Galp branching was achieved by regioselective glycosylation of disaccharide diol 21 by disaccharide 18 in 28% yield to give protected tetrasaccharide 22. Tetrasaccharide 22 was deprotected to give as its 2-(trimethylsilyl)ethyl glycoside the title compound 1a. In addition the 2-(trimethylsilyl)ethyl group was cleaved and the tetrasaccharide coupled by glycosylation (via tetrasaccharide trichloroacetimidate) to a linker suitable for conjugation.

     

Silver Trifluoromethanesulfonate(Triflate) Activation of Trichloroacetimidates in Glycosylation Reactions

Abstract

Chemical syntheses of biologically active oligosaccharides, glycolipids and glycopeptides requires efficient stereospecific glycosylation reactions.² One of the most effective glycosylation methods involves activation of anomeric imidates, particularly mchloroacetimidates, by Lewis acids such as boron trifluoride etherate (BF₃·OEt₂), mmethylsilyl mfluoromethanesulfonate (TMSOTF)³ and mfluoromethanesulfonic anhydride.⁴ In a recent example from this laboratory, BF₃·OEt₂, has been used to promote the glycosylation of methyl 2,3,6-tri-O-benzoyl-B-D-galactopyranoside (I)⁵ with 2-deoxy-2-phthalimido-3,4,6-tri-O-acetyl-B-D-galactopyranosyl mchloroacetimidate (I): see Scheme 1. The expected β1-4-linked disaccharide III was obtained in 40% yield. The yield was so low since both the α-anomer and a 1-3-linked disaccharide were formed as by products, the latter in particularly large quantities (cf. Ref.⁷). The 1-3 disaccharide could be formed from a product of acid-catalyzed 3,4-migration of the benzoyl group which is not surprising, considering the cis relationship of the 3,4-hydroxyl groups in galactose.⁸ In fact, when the glycosylation reaction was quenched before all unreacted alcohol was consumed, the chromatographic fraction corresponding to the starting alcohol II contained at least three different tribenzoates (as shown by NMR analysis).⁹ Other promoters, ZnBr₂ ¹⁰ and TMSOTF, led to lower yields and more complicated mixtures than BF₃·OEt₂.     

Selectin Receptors 4: Synthesis of Tetrasaccharides Sialyl Lewis A and Sialyl Lewis X Containing A Spacer Group1,2

ABSTRACT

Synthesis of two isomeric tetrasaccharides, namely Neu5Acα(2→3)Galβ(1→3)[Fucα(1→4)GlcNAcβ (sLe^a) and Neu5Acα(2→3)Galβ(1→4)[Fucα(1→3)]GlcNAcβ (sLe^x) as 3-aminopropyl glycosides is described. Preparation of these compounds was performed by sialylation of selectively protected trisaccharides Le^a and Le^x which contain three unsubstituted OH groups at positions 2, 3 and 4 of Gal residue. Glycosylation of Le^x trisaccharide with ethylthio sialoside under promotion by NIS and TfOH in acetonitrile was effective and regio- and stereoselective to give sLe^x derivative in 81% yield. In contrast, sialylation of the Lc^a acceptor was accompanied by a variety of undesirable by-processes, namely. N-thioethylation of the GlcNAc residue, β-sialylation, and lactonisation. In order to improve the yield of sLc^a tetrasaccharide the glycosylation of Le^a acceptor by sialyl donors of ethyl and phenyl thioglycoside (promoted by NIS-TfOH or NBS-Bu₄NBr), xanthate (promotion by NIS-TfOH mixture or MeOTf) and phosphite (promoted by TMSOTf) types was also studied. Among the reactions investigated the glycosylation by phenyl thioglycoside sialoside promoted by NIS-TfOH gives the best yield (39%) of sLe^a tetrasaccharide product.     

Optimization and modeling of synthesis parameters of neodymium(III) bromide by dry method using full factorial design analysis

The synthesis of neodymium(III) bromide (NdBr₃) by sintering brominating of neodymium oxide (Nd₂O₃) with ammonium bromide (NH₄Br) was investigated. The influence of various synthesis parameters (temperature, contact time and stoichiometry) on the reaction yield was studied and optimized. The main interaction effects of the synthesis parameters on the reaction yield were also determined by a full 2³ factorial designs with six replicates at the center point.This study showed that the optimum conditions for the synthesis of NdBr₃ are following: contact time t = 60 min, stoichiometry in moles Nd₂O₃:NH₄Br = 1:24 and temperature T = 400 °C. The reaction yield for these parameters was equal to 97.80%. The first order model was obtained to predict the reaction yield as a function of these three parameters. It was shown that all parameters have a significant positive influence on reaction yield. In addition it was pointed out also that the interaction effects between them are significant.     

Ruthenium-catalyzed intramolecular cyclization of hetero-functionalized allylbenzenes

Intramolecular addition of heterofunctionalities to CC double bonds without β-hydride elimination was investigated and catalyzed by ruthenium complexes. The combination of RuCl₃ · nH₂O (10 mol%) and 3 equiv. of AgOTf acted as a catalyst for cyclization of 2-allylphenol (1a) to 2,3-dihydro-2-methylbenzofuran (2a) in good yield in the presence of Cu(OTf)₂ as a co-catalyst and PPh₃ as a ligand. This catalyst system also catalyzed the cyclization of 2-allylbenzoic acid to lactone in 91% yield. Then, a new catalyst system (RuCp¹Cl₂)₂ (1.0 mol%)/4AgOTf/4PPh₃, was found to be more active even in the absence of Cu(OTf)₂. Furthermore, this catalysis was applied to asymmetric reaction of 2-allylphenol (1a). When using TolBINAP as a ligand, over 60% e.e. was achieved.     

Glycosyl trifluoroacetimidates. 2. Synthesis of dioscin and xiebai saponin I

Two trisaccharide steroidal saponins, dioscin (1) and Xiebai saponin I (2) with various bioactivities, were efficiently synthesized using the newly developed glycosyl N-phenyl trifluoroacetimidates (10-13) as glycosylation donors. Thus, dioscin was synthesized in five steps and a 33% overall yield from diosgenin and glycosyl trifluoroacetimidates (10 and 11). Xiebai saponin I was synthesized in eight steps and a 32% overall yield from laxogenin and glycosyl trifluoroacetimidates (10, 12, and 13), whereupon, the rare steroid laxogenin was prepared from diosgenin in four steps and an overall 69% yield. All the glycosylation reactions involved in the present syntheses demonstrated that glycosyl trifluoroacetimidates were successful donors comparable to the corresponding glycosyl trichloroacetimidates.