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.     

Efficient synthesis of the structural core of tetracyclines by a palladium-catalyzed domino Tsuji-Trost-Heck-Mizoroki reaction

The Pd-catalyzed domino Tsuji-Trost-Heck-Mizoroki reactions of compounds 18, 27, and 34, respectively, each containing an allyl acetate and a halogen aryl moiety, lead to the formation of hexahydronaphthacenes 2 and 3 and octahydroanthracene 4 in 62-81 % yield. The octahydroanthracene and hexahydronaphthacene motifs are found in many natural products, for example, the tetracycline antibiotics.     

Dimethylaluminium aldiminophenolates: synthesis, characterization and ring-opening polymerization behavior towards lactides

The stoichiometric reaction of the salicylaldimine derivatives (L1-L12) with trimethylaluminium afforded the corresponding dimethylaluminium aldiminophenolates (C1-C12), which were fully characterized by NMR spectroscopy and elemental analysis. The molecular structures of the representative complexes C1, C6, and C8 were determined by the single-crystal X-ray diffraction, which revealed distorted tetrahedral geometry at aluminium. Activation of the dimethylaluminium aldiminophenolates for the ring-opening polymerization required one equivalent of BnOH. On the basis of the polymerization results for l-lactide, d-lactide or rac-lactide, higher efficiency was observed for the ROP of d-lactide, and the nature of the ligands present significantly affected the observed catalytic activities and the properties of the resultant polylactides.     

Studies toward the total synthesis of diterpene antibiotic guanacastepene A: construction of the hydroazulenic core

[reaction: see text] As a part of studies aimed toward the total synthesis of biologically important natural product guanacastepene A of contemporary interest, a new and concise route to a fully functionally endowed hydroazulenic core is delineated. The strategy involves the building of the requisite stereochemical features on a endo-tricyclo[5.2.1.0(2,6)]decane matrix and excision of the five-membered ring through a retro-Diels-Alder reaction. Generation of the seven-membered ring to access the hydroazulenic framework was achieved employing ring closure metathesis (RCM) reaction as the key step.     

A total synthesis of distamycin a,an antiviral antibiotic

A new total synthesis of distamycin A (1) is described. The route followed passes through an intermediate acid (2a) which can serve as a convenient starting material for the synthesis of distamycin analogs.     

Total synthesis of BE-23254, a chlorinated angucycline antibiotic

The first synthesis of BE-23254, an unusual angucycline antibiotic, is reported. It involves regioselective condensation of naphthalenone 4 and chlorine-containing isobenzofuranone 16 as the key step.     

模板法合成含中心功能基Schiff型大环化合物的研究

报道了一种利用Ba^2+,Sr^2+作为模板离子直接合成含中心功能基Schiff型大 环化合物的方法。并通过元素分析，IR，^1H NMR及MS确定其新化合物的结构。     

Efficient, diastereoselective chemical synthesis of a beta-mannopyranosyl phosphoisoprenoid

[reaction: see text] Tetrabutylammonium benzyl dihydrophytylphosphate was coupled to S-phenyl 2,3-di-O-benyl-4, 6-O-benzylidene-1-thio-alpha-D-mannopyranoside S-oxide on activation with triflic anhydride in toluene at -78 degrees C to give the corresponding beta-mannosyl phosphate in 56% yield with no detectable formation of the alpha-anomer. Treatment with sodium in liquid ammonia then afforded the unprotected beta-mannosyl phosphoisoprenoid.     

Theoretical study on polynuclear superalkali cations with various functional groups as the central core

A new series of polynuclear superalkali cations YLi(3)(+) (Y = CO(3), SO(3), SO(4), O(4), and O(5)) has been created when the central group is surrounded by alkali atoms. The structural characteristics and stabilities of these systems are provided on the basis of ab initio methods. In the lowest-energy structure of the CO(3)Li(3)(+), SO(3)Li(3)(+), and SO(4)Li(3)(+) cations, the central Y (Y = CO(3), SO(3), and SO(4)) group features a slight distortion. The global minima of O(4)Li(3)(+) and O(5)Li(3)(+) are of the forms O(2)(-)(Li(+))(3)O(2)(-) and O(2)(-)(Li(+))(3)O(3)(-), respectively, both of which contain two monovalent ion units. The structural integrity of the central Y group and the arrangement of the lithium ligands are two influencing factors on the vertical electron affinities (EA(vert)) for the YLi(3)(+) species. The YLi(3)(+) cation, with its lithium ligands being distributed evenly or far from each other, tends to exhibit a low EA(vert) value, whereas a greater extent of cleavage of the central Y group leads to a higher EA(vert) value and even makes some species lose their superalkali nature.     

Efficient synthesis of core 2 class glycosyl amino acids by one-pot glycosylation approach

We describe the one-pot synthesis of core 2 class branched oligosaccharides initiated by chemo-selective glycosylation of silyl ether. Glycosylation of 6-O-silyl-4-benzyl-2-azido-thiogalactoside with glycosyl fluoride provided selectively 6-glycosylated thioglycoside without both O-glycosylation at the 3 position and S-glycosylation. Subsequent coupling of galactosyl fluoride and amino acids afforded the protected branched oligosaccharides in good yields.     

Structure and total synthesis of chryscandin,a new antifungal antibiotic

The structure elucidation and total synthesis of chryscandin (1), a new antifungal antibiotic produced by $\text{Chrysosporium pannorum}$ No.4629, is reported.     

The first total synthesis of lactonamycin, a hexacyclic antitumor antibiotic

The total synthesis of lactonamycin has been achieved. The synthesis includes sequential intramolecular conjugate addition of alcohols to the acetylenic ester, stereoselective glycosylation of the tertiary alcohol, and Michael-Dieckmann type cyclization with the thioester, by which the highly convergent route has been established.     

Solid-phase synthesis of dihydrovirginiamycin S1, a streptogramin B antibiotic

We describe the first solid-phase synthesis of dihydrovirginiamycin S(1), a member of the streptogramin B family of antibiotics, which are nonribosomal-peptide natural products produced by Streptomyces. These compounds, along with the synergistic group A components, are "last line of defense" antimicrobial agents for the treatment of life-threatening infections such as vancomycin-resistant enterococci. The synthesis features an on-resin cyclization and is designed to allow production of streptogramin B analogues with diversification at positions 1', 1, 2, 3, 4, and 6. Several synthetic challenges known to hinder the synthesis of this class of compounds were solved, including sensitivity to acids and bases, and epimerization and rearrangements, through the judicious choice of deprotection conditions, coupling conditions, and synthetic strategy. This work should enable a better understanding of structure-activity relationships in the streptogramin B compounds, possible identification of analogues that bypass known resistance mechanisms, and perhaps the identification of analogues with novel biological activities.     

Total synthesis of landomycin A, a potent antitumor angucycline antibiotic

The first total synthesis of landomycin A, the longest and most potent antitumor angucycline antibiotic, has been achieved in 63 steps and 0.34% overall yield starting from 2,5-dihydroxybenzoic acid, 3,5-dimethylphenol, triacetyl d-glucal, and d-xylose, with a convergent linear sequence of 21 steps.     

Efficient synthesis of the core structure of muraymycin and caprazamycin nucleoside antibiotics based on a stereochemically revised sulfur ylide reaction

The reaction of protected uridine 5′-aldehydes with sulfur ylides has been reinvestigated. Further transformation of the resulting epoxide product provided a compound of which a single crystal for X-ray diffraction was obtained. As a consequence from the elucidated structure, the stereochemical configuration of the epoxide furnished by the sulfur ylide reaction was revised. Based on these results, an efficient synthesis of the core structure of the naturally occurring muraymycin and caprazamycin nucleoside antibiotics was developed.     

Efficient one-pot synthesis of the 2-aminocarbonylpyrrolidin-4-ylthio-containing side chain of the new broad-spectrum carbapenem antibiotic ertapenem

An efficient synthesis of the 2-aminocarbonylpyrrolidin-4-ylthio containing side chain of ertapenem (MK-0826) is described. Starting material N-(O,O-diisopropyl phosphoryl)-trans-4-hydroxy-L-proline is converted in a one-pot process to (2S)-cis-3-[[(4-mercapto-2-pyrrolidinyl)carbonyl]amino]benzoic acid monohydrochloride in 70-75% overall yield via a series of six reactions. The development of each of these reactions and the isolation of the product is discussed in detail.     

An asymmetric synthesis of (+)-grandisol, a constituent of the aggregation pheromone of the cotton boll weevil, via a kinetic resolution

A novel approach to the asymmetric synthesis of (+)-grandisol, (1R, 2S)-isopropenyl-1-methylcyclobutaneethanol, involves the use of catalytic kinetic resolution of a primary allylic alcohol, [(1RS, 5SR)-5-methylbicyclo[3.2.0]hept-2-en-2-yl] methanol. The allylic alcohol is prepared in four steps from simple achiral materials involving the use of a modified Shapiro reaction. The resolved alcohol (95% ee) is then reduced in two steps to the corresponding methyl alkene, (1S,5R)-2,5-dimethylbicyclo[3.2.0]hept-2-ene. This alkene is converted to (+)-grandisol (95% ee), in three steps, by modified literature procedures.     

Enantiodivergent synthesis of both enantiomers of marine alkaloids haliclorensin and isohaliclorensin, a constituent of halitulin

Starting from (3R)-5-benzotriazolyl-3-phenylperhydropyrido[2,1-b][1,3]oxazole 9, the enantiodivergent syntheses of both enantiomers of the marine alkaloids haliclorensin 1 and isohaliclorensin 3 have been achieved. Our syntheses feature ring-expansion reactions for the formation of the aza-macrocycle ring system of 3 and sequential ring-expansion reactions (aza-Claisen rearrangement and Zip reaction) for the formation of the aza-macrocycle ring system of 1.     

Complete synthesis of the antibiotic anisomycin

The synthesis of the antibiotic anisomycin ( 1 ) is described. In the key step 3, 4-dimethoxy-thiopyrrolidone ( 16 ), prepared from diethyl L -( + )-tartarate ( 4 ) was converted to the thioiminoester 18 , which upon treatment with trimethylphosphite yielded the benzylidene derivative 19 . Cleavage of the ester group of 19 and hydrogenation of the decarboxylation product gave the two isomers 21 and 22 . 22 was converted into desacetylanisomycin ( 3 ) and anisomycin ( 1 ).