Multi-component one-pot synthesis of the tumor-associated carbohydrate antigen Globo-H based on preactivation of thioglycosyl donors

Two efficient routes for the rapid assembly of the tumor-associated carbohydrate antigen Globo-H hexasaccharide 2 by a preactivation based iterative one-pot strategy are reported. The first method involves the sequential coupling of four glycosyl building blocks, leading to the desired hexasaccharide in 47% overall yield in one-pot synthesis. Although model studies on constructing the challenging Gal-alpha-(1-4)-Gal linkage in Gb3 trisaccharide yielded the desired alpha linkage almost exclusively, a similar approach to assemble the hexasaccharide led to the formation of a significant amount of beta anomer. As an alternative, the second synthesis utilized three components in one pot with the Gal-alpha-(1-4)-Gal linkage preformed, producing the desired hexasaccharide in a similar overall yield as the four component approach. Both methods demonstrate that oligosaccharides containing alpha and beta linkages within the same molecule can be constructed in one pot via a preactivation based approach with higher glyco-assembly efficiencies than the automated solid-phase synthesis strategy. Furthermore, because glycosylations can be carried out independent of anomeric reactivities of donors, it is not necessary to differentiate anomeric reactivities of building blocks through extensive protective group adjustment for chemoselective glycosylation. This confers great flexibilities in the building block design, allowing matching of the donor with the acceptor, leading to improved overall yield.     

与癌症相关的糖类抗原Globo-H六糖的全合成进展

Globo-H作为一种和乳腺癌、前列腺癌相关的复杂糖类抗原,其发现为糖类疫苗开发和癌症免疫治疗带来了机遇,但如何高效、高纯地获得合成糖类抗原,以供研究和临床应用,也向寡糖合成方法学提出了挑战.综述了1995年Danishefsky首次以糖烯组装策略全合成Globo-H以来的各种新方法,如:Schmidt的三氯乙酰亚胺酯法、Boons的双向糖苷化法、Wong的基于糖基给体活性差异的一锅煮策略、Seeberger的液相线性合成和固相自动组装法、Huang的多组份反复预活化一锅煮法和最新报道的酶法.就糖合成方法学而言,硫苷法依旧可称为"明星方法",糖烯、三氯乙酰亚胺酯和氟代糖也普遍采用,磷酸酯糖基给体在固相合成中的应用正显示出其新的活力.这些方法代表了当今糖化学的水平和发展趋势.     

Pursuit of optimal carbohydrate-based anticancer vaccines: preparation of a multiantigenic unimolecular glycopeptide containing the Tn, MBr1, and Lewis(y) antigens.

A novel preparation of nonnatural glycoamino acids starting from n-pentenyl glycosides is described. The approach involves a Horner-Emmons olefination with a suitably protected glycine-derived phosphonate, followed by catalytic asymmetric hydrogenation, which proceeds with excellent diastereomeric selectivity. The synthetic methodology was useful for the preparation of glycoamino acids containing the Tn antigen, the MBr1 antigen (Globo-H), the Le(y) antigen, and lactose. These glycoamino acids can also serve as units for peptide synthesis. The synthesis of polyvalent glycopeptides containing three different antitumor antigens is described (28 and 29), and these have been prepared for conjugation to carrier protein in order to access the immunogenicity for tumor immunotherapy applications.     

Synthesis and characterisation of a ligand that forms a stable tetrahedral intermediate in the active site of the Aureobacterium species (-) gamma-lactamase

The crystal structure of a (-) gamma-lactamase from an Aureobacterium species showed a molecule bound covalently to the active site serine residue. This enzyme complex represented the first structure of a stably bound tetrahedral intermediate for an alpha/beta hydrolase fold enzyme. The structural elucidation of tetrahedral intermediates is important for the understanding of enzymatic mechanism, substrate recognition and enzyme inhibition. In this paper, we report the synthesis and subsequent characterisation of (3aR,7aS)-3a,4,7,7a-tetrahydrobenzo-[1,3]-dioxol-2-one (BD1), the molecule modelled into the Aureobacterium (-) gamma-lactamase active site. This molecule has been confirmed to be an inhibitor and to be displaced from the enzyme by the racemic gamma-lactam substrate.     

Synthesis of DOTA-conjugated multivalent cyclic-RGD peptide dendrimers via 1,3-dipolar cycloaddition and their biological evaluation: implications for tumor targeting and tumor imaging purposes

This report describes the design and synthesis of a series of alpha(V)beta(3) integrin-directed monomeric, dimeric and tetrameric cyclo[Arg-Gly-Asp-d-Phe-Lys] dendrimers using "click chemistry". It was found that the unprotected N-epsilon-azido derivative of cyclo[Arg-Gly-Asp-d-Phe-Lys] underwent a highly chemoselective conjugation to amino acid-based dendrimers bearing terminal alkynes using a microwave-assisted Cu(I)-catalyzed 1,3-dipolar cycloaddition. The alpha(V)beta(3) binding characteristics of the dendrimers were determined in vitro and their in vivoalpha(V)beta(3) targeting properties were assessed in nude mice with subcutaneously growing human SK-RC-52 tumors. The multivalent RGD-dendrimers were found to have enhanced affinity toward the alpha(V)beta(3) integrin receptor as compared to the monomeric derivative as determined in an in vitro binding assay. In case of the DOTA-conjugated (111)In-labeled RGD-dendrimers, it was found that the radiolabeled multimeric dendrimers showed specifically enhanced uptake in alpha(V)beta(3) integrin expressing tumors in vivo. These studies showed that the tetrameric RGD-dendrimer had better tumor targeting properties than its dimeric and monomeric congeners.     

Construction of highly glycosylated mucin-type glycopeptides based on microwave-assisted solid-phase syntheses and enzymatic modifications

A MUC1-related glycopeptide having five core-2 hexasaccharide branches (C330H527N46O207, MW = 8450.9) was synthesized by a new strategy using a combination of microwave-assisted solid-phase synthesis (MA-SPGS) and enzymatic sugar elongation. Synthesis of a key glycopeptide intermediate was best achieved in a combination of PEGA [poly(ethylene glycol)-poly-(N,N-dimethylacrylamide) copolymer] resin and MA-SPGS using glycosylated amino acid building blocks with high speed and high purity. Deprotection of the glycopeptide intermediate and subsequent glycosyltransferase-catalyzed sugar elongations were performed for generation of the additional diversities with the sugar moieties of glycopeptides using beta1,4-galactosyltransferase (beta1,4-GalT) and two kinds of alpha2,3-sialyltransferases [ST3Gal III; alpha2,3-(N)-SiaT and ST3Gal II; alpha2,3-(O)-SiaT]. These reactions proceeded successfully in the presence of 0.2% Triton X-100 to convert the chemically synthesized trisaccharide glycans to disialylated hexasaccharide.     

Construction and structural characterization of versatile lactosaminoglycan-related compound library for the synthesis of complex glycopeptides and glycosphingolipids

We have established a facile and efficient protocol for the preparative-scale synthesis of various compound libraries related to lactosaminoglycans: cell surface oligosaccharides composed of N-acetyllactosamine as a repeating disaccharide unit, based on chemical and enzymatic approaches. Substrate specificity and feasibility of a bacterial glycosyltransferase, Neisseria meningitidis beta1,3-N-acetylglucosaminyltransferase (LgtA), were investigated in order to synthesize various key intermediates suited for the construction of mammalian O-glycopeptides and glycosphingolipids containing poly-N-acetyllactosamine structures. Recombinant LgtA exhibited the highest glycosyltransferase activity with strongly basic conditions (pH = 10, glycine-NaOH buffer) and a broad range of optimal temperatures from 20 to 30 degrees C. Interestingly, it was found that LgtA discriminates L-serine and L-threonine and functions both as a core-1 beta1,3-N-acetylglucosaminyltransferase and core-2 beta1,3-N-acetylglucosaminyltransferase toward Fmoc-Ser derivatives, while LgtA showed only core-2 beta1,3-N-acetylglucosaminyltransferase activity in the presence of Fmoc-Thr derivatives. Combined use of LgtA with human beta1,4-galactosyltransferase allowed for controlled sugar extension reactions from synthetic sugar amino acids and gave synthetic lactosaminoglycans, such as a decasaccharide derivative, Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Ser-OH (6), and a dodecasaccharide derivative, Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Ser-OH (9). A partially protected pentasaccharide intermediate, GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Thr-OH (11), was applied for the microwave-assisted solid-phase synthesis of a MUC1-related glycopeptide 19 (MW = 2610.1). The findings suggest that this sugar extension strategy can be employed for the modification of lactosyl ceramide mimetic polymers to afford convenient precursors for the synthesis of various glycosphingolipids.     

Probing the substrate specificity of Golgi alpha-mannosidase II by use of synthetic oligosaccharides and a catalytic nucleophile mutant

Inhibition of Golgi alpha-mannosidase II (GMII), which acts late in the N-glycan processing pathway, provides a route to blocking cancer-induced changes in cell surface oligosaccharide structures. To probe the substrate requirements of GMII, oligosaccharides were synthesized that contained an alpha(1,3)- or alpha(1,6)-linked 1-thiomannoside. Surprisingly, these oligosaccharides were not observed in X-ray crystal structures of native Drosophila GMII (dGMII). However, a mutant enzyme in which the catalytic nucleophilic aspartate was changed to alanine (D204A) allowed visualization of soaked oligosaccharides and led to the identification of the binding site for the alpha(1,3)-linked mannoside of the natural substrate. These studies also indicate that the conformational change of the bound mannoside to a high-energy B 2,5 conformation is facilitated by steric hindrance from, and the formation of strong hydrogen bonds to, Asp204. The observation that 1-thio-linked mannosides are not well tolerated by the catalytic site of dGMII led to the synthesis of a pentasaccharide containing the alpha(1,6)-linked Man of the natural substrate and the beta(1,2)-linked GlcNAc moiety proposed to be accommodated by the extended binding site of the enzyme. A cocrystal structure of this compound with the D204A enzyme revealed the molecular interactions with the beta(1,2)-linked GlcNAc. The structure is consistent with the approximately 80-fold preference of dGMII for the cleavage of substrates containing a nonreducing beta(1,2)-linked GlcNAc. By contrast, the lysosomal mannosidase lacks an equivalent GlcNAc binding site and kinetic analysis indicates oligomannoside substrates without non-reducing-terminal GlcNAc modifications are preferred, suggesting that selective inhibitors for GMII could exploit the additional binding specificity of the GlcNAc binding site.     

Chemoenzymatic synthesis of sialylated glycopeptides derived from mucins and T-cell stimulating peptides.

The Tn, T, sialyl-Tn, and 2,3-sialyl-T antigens are tumor-associated carbohydrate antigens expressed on mucins in epithelial cancers, such as those affecting the breast, ovary, stomach, and colon. Glycopeptides carrying these antigens are of interest for development of cancer vaccines and a short, chemoenzymatic strategy for their synthesis is reported. Building blocks corresponding to the Tn (GalNAc alpha-Ser/Thr) and T [Gal beta(1-->3)GalNAc alpha-Ser/Thr] antigens, which are relatively easy to obtain by chemical synthesis, were prepared and then used in the synthesis of glycopeptides on the solid phase. Introduction of sialic acid to give the sialyl-Tn [Neu5Ac alpha(2-->6)GalNAc alpha-Ser/Thr] and 2,3-sialyl-T [Neu5Ac alpha(2-->3)Gal beta(1-->3)GalNAc alpha-Ser/Thr] antigens is difficult when performed chemically at the building block level. Sialylation was therefore carried out with recombinant sialyltransferases in solution after cleavage of the Tn and T glycopeptides from the solid phase. In the same manner, the core 2 trisaccharide [Gal beta 1-->3(GlcNAc beta 1-->6)GalNAc] was incorporated in glycopeptides containing the T antigen by using a recombinant N-acetylglucosaminyltransferase. The outlined chemoenzymatic approach was applied to glycopeptides from the tandem repeat domain of the mucin MUC1, as well as to neoglycosylated derivatives of a T cell stimulating viral peptide.     

Carboracycles: Macrocyclic Compounds Composed of Carborane Icosahedra Linked by Organic Bridging Groups

A family of macrocyclic compounds are described, together with their precursors. These cycles are composed of icosahedral carboranes linked via their carbon vertices through 1,3-trimethylene, alpha,alpha'-1,3-xylylene, or alpha,alpha'-2,6-lutidylene groups. The compounds cyclo-(1,3-trimethylene-1',2'-closo-1',2'-C(2)B(10)H(10))(4) (6a), cyclo-(1,3-trimethylene-1',2'-closo-9',12'-dimethyl-1',2'-C(2)B(10)H(8))(4) (6b), cyclo-(1,3-trimethylene-1',2'-closo-1',2'-C(2)B(10)H(10))(3) (9), cyclo-(alpha,alpha'-1,3-xylylene-1',2'-closo-1',2'-C(2)B(10)H(10))(2) (11a), cyclo-(alpha,alpha'-1,3-xylylene-1',7'-closo-1',7'-C(2)B(10)H(10))(2) (11b), cyclo-(alpha,alpha'-1,3-xylylene-1',7'-closo-9',10'-dimethyl-1,7-C(2)B(10)H(8))(2) (11c), cyclo-(alpha,alpha'-1,3-xylylene-1',2'-closo-1',2'-C(2)B(10)H(10))(4) (12), cyclo-(alpha,alpha'-1,3-xylylene-1',7'-closo-1',7'-C(2)B(10)H(10))(3) (13), cyclo-(alpha,alpha'-2,6-lutidylene-1',7'-closo-1',7'-C(2)B(10)H(10))(2) (19), and cyclo-(alpha,alpha'-2,6-lutidylene N-oxide-1',7'-closo-1',7'-C(2)B(10)H(10))(2) (20) have been synthesized. The structures of 6a, 6b, 9, 11a, 11b, 11c, 12, and 19 have been determined by X-ray crystallography. Crystal data: for 6a, triclinic, space group P&onemacr;, a = 11.131(2) ?, b = 12.642(2) ?, c = 12.996(2) ?, alpha = 84.383(6) degrees, beta = 65.884(6) degrees, gamma = 97.292(5) degrees, Z = 1, R = 0.079; for 6b, monoclinic, space group P2(1)/a, a = 13.500(2) ?, b = 31.141(3) ?, c = 13.831(2) ?, beta = 99.90(1) degrees, Z = 2, R = 0.097; for 11a, monoclinic, space group C2/c, a = 14.5682(8) ?, b = 14.5046(8) ?, c = 16.1998(8) ?, beta = 95.631(2) degrees, Z = 4, R = 0.081; for 11b, monoclinic, space group P2(1)/n, a = 11.650(2) ?, b = 10.606(2) ?, c = 11.730(2) ?, beta = 104.951(6) degrees, Z = 2, R = 0.069; for 11c, orthorhombic, space group Pbca, a = 12.532(2) ?, b = 14.271(2) ?, c = 18.143(3) ?, Z = 4, R = 0.076; for 19, orthorhombic, space group Pcab (No. 61, standard setting Pbca), a = 11.0428(6) ?, b = 11.3785(6) ?, c = 22.533(1) ?, Z = 4, R = 0.074.     

Carbocyclic analogues of nucleosides from bis-(Hydroxymethyl)-cyclopentane: synthesis,antiviral and cytostatic activities of adenosine,inosine and uridine analogues

Six new carbocyclic nucleosides were prepared by constructing a purine base (in compounds 9-11) or pyrimidine base (in 6-8) on the amino groups of (+/-)-(1 beta,2 alpha,4 beta)-4-amino-1,2-cyclopentanedimethanol (4) and (+/-)-(1 beta,3 alpha,4 beta)-4-amino-1,3-cyclopentanedimethanol (5), and their activities against a variety of viruses and tumour cell lines were determined.     

A practical and scaleable total synthesis of the jaborandi alkaloid (+)-pilocarpine

The total synthesis of (+)-pilocarpine (as its nitrate salt) has been achieved in nine steps and 30% overall yield starting from racemic 2-(2′,2′-dimethoxyethyl)propane-1,3-diol, which was desymmetrised via an enzymatic protocol. A high yielding synthesis of a key α-ethylidene lactone precursor has been developed, which involves the palladium-catalysed decarboxylation/carbonylation of a 1,3-dioxan-2-one for formation of the γ-butyrolactone ring. Subsequent hydrogenation of the α-ethylidene lactone introduces the C(3)-stereochemistry to give a 72:28 mixture of (+)-pilocarpine and (+)-isopilocarpine, which are readily separable via recrystallisation of the (+)-pilocarpine nitrate salt.     

Biomimetic synthesis of resorcylate natural products utilizing late stage aromatization: concise total syntheses of the marine antifungal agents 15G256iota and 15G256beta

Diketo-1,3-dioxin-2-ones underwent retro-Diels-Alder reaction on heating in toluene at 110 degrees C to generate alpha,gamma,-triketo-ketenes. These were trapped with alcohols to provide 2,4,6-triketocarboxylates, which were smoothly aromatized by sequential reaction with potassium carbonate and methanolic hydrogen chloride to give resorcylate esters. The reaction was applied in the total synthesis of the marine antifungal agents 15G256beta (1), 15G256iota (2), and 15G256pi (3) and the mycotoxin S-(-)-zearalenone (4).     

Diastereoselective synthesis of protected syn 1,3-diols: preparation of the C16-C24 portion of Dolabelides

We have designed a new method to make synthons encompassing a protected syn 1,3-diol motif and an aldehyde alpha to the 1,3-dioxane ring. An additional stereocenter was also created, potentially leading to stereochemically defined 1,2,4-triols. This method was successfully applied to the synthesis of the C16-C24 portion of Dolabelides.     

Synthesis of non-natural glycosylamino acids containing tumor-associated carbohydrate antigens

The synthesis of biologically relevant glycosylamino acids using a non-natural amino acid as the glycosyl acceptor is described. The glycosylation reaction of a monosaccharide tri-chloroacetimidate donor with Fmoc-l-hydroxynorleucine benzyl ester provided the α-O-linked product. Conversely, when the glycosylation reaction was carried out with a glycal epoxide donor, the β-O-linked product predominated. We have used these two complementary glycosylation reactions to synthesize five different glycosylamino acids, each containing the Tn, TF, STn, Lewis^y or Globo-H tumor-associated carbohydrate antigens.     

1,3-偶极环加成反应修饰卟啉化合物

利用1,3-偶极环加成反应对卟啉大环进行修饰是近年来卟啉研究的一个新热点。环加成产物因在可见光谱长波段范围的特征吸收,在构筑人工光反应体系和用作光动力疗法中的光敏剂等领域有重要应用价值。本文综述了1,3-偶极环加成反应在修饰卟啉化合物方面的研究进展,包括：卟啉作为亲偶极体能与甲亚胺叶立德、硝酮、重氮烷、羰基叶立德、腈氧化物等1,3-偶极子反应生成各种新型杂环稠合卟吩类化合物;卟啉化合物作为1,3-偶极子能与C₆₀等亲偶极体反应,生成β位取代的各种新型卟啉化合物;以及扩展卟啉也可以作为亲偶极体与甲亚胺偶极子发生1,3-偶极环加成反应等。     

Regioselective synthesis of functionalized 3,5-diketoesters and 2,4-diketosulfones by uncatalyzed condensation of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadienes with alpha,beta-unsaturated acid chlorides and sulfonyl chlorides

The reaction of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadienes with alpha,beta-unsaturated and functionalized acid chlorides afforded a variety of 3,5-diketoesters which are not readily available by other methods. The reaction of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadiene with sulfonyl chlorides allows a direct synthesis of 2,4-diketosulfones.     

Synthesis of functionalized alpha,alpha-disubstituted beta-alkynyl esters from allenoates through an alkynylenolate intermediate

Highly substituted alpha,alpha-disubstituted beta-alkynyl esters are readily prepared from allenyl esters and either alkyl halide, acid chloride, or alkyl chloroformate, mediated by an amide base. This highly efficient and mild process tolerates various functional groups and provides alpha,alpha-disubstituted beta-alkynyl esters in good to excellent yields. This method is especially suitable for the synthesis of 1,n-enynes or 1,n-diynes (n > 4). Electrophilic cyclization of 1,5-enyne gives a highly functionalized gamma-iodolactone, whereas its platinum-catalyzed cycloisomerization affords 1,3-cyclohexadiene.     

Novel chiral lipoxygenase substrates: design and synthesis. Part 2

A series of novel lipoxygenase substrates carrying a spacing modifier with a non-ionic hydroxyl terminus have been synthesized in an enantioselective fashion. One of the methylene hydrogens (flanked by the cis,cis-pentadienyl moiety) is replaced by alkyl, aryl and hydroxyl groups. The key steps in the synthesis involved enzymatic transesterification of 1,3-propanediol derivatives and two consecutive cis-selective Wittig olefinations.     

Enantioselective 1,3-dipolar cycloadditions of diazoacetates with electron-deficient olefins

[reaction: see text] A general strategy for highly enantioselective 1,3-dipolar cycloaddition of diazoesters to beta-substituted, alpha-substituted, and alpha,beta-disubstituted alpha,beta-unsaturated pyrazolidinone imides is described. Cycloadditions utilizing less reactive alpha,beta-disubstituted dipolarophiles require elevated reaction temperatures, but still provide the corresponding pyrazolines with excellent enantioselectivities. Finally, an efficient synthesis of (-)-manzacidin A employing this cycloaddition methodology as a key step is illustrated.