Search

Synthetic 3-O-methylmannose containing polysaccharide (sMMPS) were designed and synthesized. The procedure involves five glycosidations and produces sMMP-8-, 12-, and 16mers and it was found that the synthetic and natural MMPs exhibit almost similar properties.

Synthetic 6-O-methyl-D-glucose containing polysaccharides (sMGPs) were designed and synthesized from [alpha], [beta] and [gamma]-cyclodextrins (CDs). Results show that the amount of Mukaiyama acid required in the sMGP series increased with an increase of substrate size.

A study to determine the differences between the spectroscopic data of the isolated and synthetic samples of the marine natural product (+)-elisabethadione and (+)-elisabethamine was conducted. Results concluded that the published NMR spectral data for natural (+)-elisabethadione do not fit the assigned structure and raises doubt about the (+)-elisabethamine structure.

Asymmetric reduction of ketimines with trichlorosilane, which could be catalyzed by N-methylvaline-derived Lewis-basic formamides, is described. The results reveal that appending a fluorous tag simplifies the isolation procedure, while preserving high enantioselectivity.

The structure and acidity of the dimethylhalonium ions were studied at the Density Functional Theory level of calculations. Results indicated that upon proton transfer to form the dimethylhalonium ylide, the C-X-C bond angle increases and there are modifications in the C-X bond lengths, indicative of hyperconjugation between the electron pair with the C-X antibonding orbital.

Attempts to apply the (super 1)H NMR ABX method for assignment of stereochemistry of beta-hydroxy ketones to aldols 4-10 deriving from alpha-methyl aldehydes lacking beta-branches reveals that the presence of a beta-branch in the aldehyde reaction partner is necessary so that the average chemical environment of Ha and Hb is different for the Felkin and anti-Felkin aldols. This analysis provides provides a rational basis for application of the (super 1)H NMR ABX pattern analysis to other beta-hydroxy ketone derivatives.

Benzalacetone analogues of naphth[1,2-a]azulene, naphth[a]azulenes and naphth [2,3-a]azulene were synthesized from 2-(5-methyl-2-furyl)-1-tropylionaphthalene, 1-(5-methyl-2-furyl)-2-tropylionaphthalene and 2-(5-methy-2-furyl)-3-tropylionaphthalene respectively. Single-crystal X-ray work on the napth[1,2-a]azulene derivative revealed that its tetracyclic system exhibited deformation from planarity similar to that of benzo-[c]phenanthrene.

A practical synthesis of benzisoxazole and its conversion to alpha-aryloxyisobutyric acid using 1,1,1-trichloro-2-methyl-2-propanol is developed. A highly reactive, short-lived intermediate derived from chloretone is detected by ReacIR and its half-life determined to be ~5 min.

A tetra L-prolinylmethyl derivative of a tetra-sulfonated calix[4]resorcarenes is an effective chiral NMR solvating agent for water-soluble compounds with phenyl, pyridyl, bicyclic aromatic, or indole rings. The effectiveness of a calix[4]resorcarenes prepared from N-methyl-L-alanine as a chiral NMR discriminating agent is compared to the L-prolinylmethyl derivative. for other types of water-soluble organic salts is described.

The beta-carbolinone core structure present in a variety of alkaloids was efficiently prepared from 5-oxo-1,2,3,5-terahydroindolozine-6-trifluoromethanesulfonate precursors. Allylation of methyl 6-hydroxy-5-oxo-1,2,3,5-tetrahydroindolizine-8-carboxylate gave the corresponding ethers, which subsequently underwent thermal Claisen rearrangement to afford the C-allyl products in high yields.

A study investigates the kinetic resolution of a range of methyl-substituted 1-oxaspirol[2.5]octanes by yeast epoxide hydrolase (YEH) from Rhodotorula glutinis. The structural determinants of substrate specificity and stereoselectivity of YEH toward these substrates appears to be the configuration of the epoxide ring and the substitution pattern of the cyclohexane ring.

The conformations and properties of benzimidazole cavitand with four benzimidazole flaps are studied by (super 1)H NMR. The benzimidazole cavitand could form very stable vase structures with an enforced concave cavity by intermolecular hydrogen bonding with four hydroxyl-containing molecules, X-OH, such as methanol, acetic acid, and trifluoroacetic acid.

A report that regioselective distal bond cleavage of methylenecyclopropanes is accomplished, irrespective of the structure of the substituent R(super 1), by using the cyclic amides. The selectivity of the respective ring-opening position depends on the substituents of methylenecyclopropanes.

Taking advantage of the access to quaternary stereogenic centers through stereospecific addition of nucleophiles at C-5, starting from silyloxypyrrole 7, to achieve an efficient and highly diastereoselective synthesis of marine sponge metabolite dysibetaine, as well as deoxy and 4-epi analogues.

The synthesis and chiral recognition ability of enantiopure ABI and the chiral recognition mechanism for racemic arylalkanoic acids. X-ray crystallographic study revealed that the higher and wider chiral recognition ability of ABI than that of AI arose from effective and tunable CH [sp (super 2)]/Pi and CH [sp (super3)]/Pi interactions, for which the naphthyl group of ABI plays a very important role.

A novel, mild method is described to synthesize 6-methylidene penem compounds. This process provides a useful variation of C-C bond formation method for penem derivatives and also serves as a practical synthetic method to prepare 6-exomethylenepenem derivatives without racemization at the C5 position.

Structures and energies of protonated and methylated dimethyl sulfoxide cations and dications were calculated using the density functional theory method. The O-protonated structure 2 is 37.0 kcal/mol more stable than the S-protonated 3.

The synthesis, characterization and dynamic nature of gem-dimethyl-functionalized cyclooctapyrrole and cyclododecapyrrole are presented. Formation of the larger cyclododecapyrrole is a result of the gem-dimethyl effect.

Axially chiral 1,1'-binaphthalenyl-2,2'-diamine (BINAM) N-heterocyclic carbene (NHC)-Rh(III) complexes are applied in the enantioselective hydrosilylation of 3-oxo-3-arylpropionic acid methyl or ethyl esters. The reduction products 3-hydroxy-3-arylpropionic acid methyl or ethyl esters are obtained in good yields with excellent enantioselectivities under mild conditions.

A systematic variation of reaction conditions that has led to an efficient, straightforward synthesis of 2'-C-beta-methylguanosine with high regio- and stereoselectivity is described. The strategy also improved regioselecitivity in the synthesis of guanosine and might provide a generally useful approach for the synthesis of other guanosine nucleosides by glucosylation.

The [Me.sub.3]SiOTf-mediated condensation of 1-ethoxy-2-fluoro-1,3-bis(trimethylsilyloxy) 1,3-dienes with 3-cyanochromones to generate 3-cyano-2-(4-ethoxy-3-fluoro-2,4-dioxobutyl)chroman-4-ones is described. The product distribution in the reaction depends on the structure of the diene and the formation of the biaryls is demonstrated by an unprecedented domino 'retro-Michael/aldol/fragmentation' reaction.

A Lewis acid-mediated intramolecular cycloaddition is used to prepare bicyclic diazenium salts from [alpha]-chloroazo species. An alternative, more direct, route to bicyclic diazenium salts by the reaction of hydrazones with dimethylsulfonium ditriflate is also described.

[Super 1] NMR is used to monitor mannosazide methyl uronate donors equipped with a variety of anomeric leaving groups ([beta]- and [alpha]-S-phenyl, [beta]- and [alpha]-N-phenyltrifluoroacetimidates, hydroxyl, [beta]-sulfoxide, and ([R.sub.s])- and ([S.sub.s])-[alpha]-sulfoxides) which were subjected to activating conditions. The [beta]-S-phenyl mannosazide methyl uronate is observed to performed best in both activation experiments and glycosylation studies and provided the 1,2-cis mannosidic linkage with excellent selectivity.

One-pot synthesis of 2-aminobenzoxazoles by using commercially available tetramethyl orthocarbonate or 1,1-dichlorodiphenoxymethane, an amine, and an optionally substituted 2-aminophenol is described. The scope of the reactions conducted under mild conditions which provided 2-aminobenzoxazoles in modest to excellent yields was examined by using a variety of amines and substituted 2-aminophenols.

Macrocyclization via an efficient high-yielding solid-phase intramolecular thioalkylation reaction is described. The reactions between the S-nucleophiles and newly generated N-terminal 4-chloromethyl thiazoles resulted in the desired macrocyclization products in high purities and good overall yields.

Vorbroggen coupling of trimethylsilylated 2-N-isobutanoylguanine with peracetylated pentofuranose derivatives to generally yield inseparable N-7/N-9 glycosyl mixtures is described. The two isomers could be separated biocatalytically by Novozyme-435-mediated selective deacetylation of the 5'-O-acetyl group of peracetylated N-9 guanine nucleosides.

Sequential palladium-catalyzed Buchwald-Hartwig N-arylation reactions are used to synthesize N,N',N''-Trimethyltribenzo-1,4,7-triazacyclononatriene and obtain the 9-membered triaza o-cyclophane in 35% overall yield. An X-ray crystal structure of the new cyclophane exhibited a [C.sub.2]-symmetric saddle conformation, compared to the crown conformation exhibited by the related carbocyclic cyclotriveratrylene (CTV).

An unanticipated cleavage of 2-azido-2-(hydroxymethyl)oxetanes which are governed by conformational differences in the azidoalcohols are described. The oxidization of the title oxetanyl alcohols to the corresponding carboxylic acids with Ru[O.sub.4] to form cleaved nitriles as the sole isolable products and closely related tetrahydrofuran which gave solely the expected carboxylic acid are also reported.

Tetravinylbenzene is prepared in quantitative yield from tetrabromobenzene, where one-step procedure has used Suzuki-Miyaura cross-coupling conditions. Intramolecular cyclopropanation of monoadduct, putatively by its methyllithium-generated cyclopropylidene(oid) has produced a compound featuring a highly distorted spiropentane having a C-C-C bond angle.

A highly regioselective one-pot transformation of 2-azido-2-deoxy-1,3,4,6-tetra-O-trimethylsilyl-D-glucopyranose by sequential additions of various reagents is analyzed, which has produced the fully protected derivatives and the 1-, 3-, 4-, as well as 6-alcohols.

The synthesis and stereochemical assignment is achieved by using a regioselective anti-Markovnikov addition of water to vinylphthalide, which is accomplished by using a heteroatom-directed Wacker oxidation that has proceeded with retention of stereochemistry. The results have shown that ereverseE Wacker oxidations are a viable alternative to hydroboration/oxidation procedure.

The scope of a tandem conjugate addition-fluorination sequence performed on [alpha],[beta]-unsaturated esters by using the enantiopure lithium amide derived from (S)-N-benzyl-N-([alpha]-methylbenzyl)amine, and the electrophilic fluorinating agent N-fluorobenzenesulfonimide is examined. The method is used for preparing enantiopure [alpha]-fluoro-[[beta].sup.3]-amino acids and its utility is shown by the preparation of orthogonally protected (2S,3S)-[alpha]-fluoro-[[beta].sup.3]-lysine.

4-Hydroxy-6-methylene-2,4-cyclohexadien-1-one and 4-methoxy-6-methylene-2,4-cyclohexadin-1-one are prepared by efficient photodehydration of 2-(hydroxymethyl)benzene-1,4-diol and 2-(hydroxymethyl)-4-methoxyphenol. o-Quinone methide is decayed through two competing pathways, nucleophilic hydration to form starting material and tautomerization to produce methyl-p-benzoquinone.

Density functional theory methods are used for establishing the functional factors contributing toward the stereoselectivity in organocatalyzed asymmetric Michael reaction between aldehydes and methyl vinyl ketone (MVK). The analysis of the crucial transition states has shown that apart from steric interactions between the [alpha]-substituent and MVK, various other factors like orbital interactions and weak stabilizing hydrogen-bonding interactions have played a major role in stereoselectivity.

Irradiation of 2,5-dimethylbenzoyl oxiranes has resulted in an efficient and high-yielding formation of [beta]-hydroxy functionalized indanones that has structurally resembled biologically active pterosines. The analysis has shown complexity of the mechanism and that structural modifications can change the reaction pathway and product different products.

The application of solid phase synthesis to accelerate oligomer preparation and allow the introduction of various side chains is described. The synthesis of a tetradecameric sequence is carried out and NMR solution structural studies have shown that the alternate aminomethyl-pyridine residues have not perturbed the canonical helix folding of quinoline monomers in protic solvents.

Copper-catalyzed double thiolation reaction of 1,4-dihalides with sulfides was developed to selectively synthesizing 2-trifluoromethyl benzothiophenes and benzothiazoles. The reaction conditions are compatible with N-(2-haloaryl)trifluoroacetimidoyl chlorides in the presence of NaHS and [K.sub.3]P[O.sub.4], leading to 2-trifluoromethyl benzothiazoles.

Trimethylsilyl triflate promoted Ferrier-Petasis rearrangement of 4-(vinyloxy)-, 4-(propenyloxy)-, and 4-(isopropenyloxy)azetidin-2-ones to generate the corresponding 4-(carbonylmethyl)azetidin-2-ones is reported. The reaction and the obtained compounds might serve as attractive intermediates in the synthesis of carbapenem antibiotics.

A room temperature reaction between 1,8-Bis(dimethylamino)naphthalene (' Proton Sponge' ) and bromomaleic anhydride to generate 3-(4,5-bis(dimethylamino)napthalen-1-yl)furan-2,5-dione (4-maleicanhydridoproton sponge or 'MAPS') is described. The property of MAPS to lose color upon protonation in solution and change color on reversal indicated the ability of MAPS to act as a colorimetric version of a proton sponge.

Matrix isolation infrared spectroscopy and quantum-mechanical calculations are used to study the reaction of trimethylsilylacetylenes [Me.sub.3]SiC[triplebond]CR with Sb[F.sub.5] in the solid state. High total charges observed on the bridging Si[Me.sub.3] group and low [Me.sub.3]Si-C bond orders to acetylenic moiety, both calculated at the MP4(SDQ)/6-311G(d,p) level of theory, indicated high silyl cation character of these species.

A newly developed strategy consisting of allylsilane ring-closing metathesis and subsequent SE' electrophilic desilylation (allylsilane RCM/SE') to construct exo-methylidenecycloalkanes is described. The method helped to identified a novel metal alkylidene-promoted deallylation reaction of terminal 1,4-dienes and provided a possible mechanism for the unexpected deallylation reaction of 1,4-dienes.

The highly reactive Grignard reagents were introduced with bis[2-(N,N'-dimethylamino)ethyl] ether (BDMAEE) to effectively deactivate their reactivity and achieve a highly enantioselective alkylation of aldehydes with Grignard reagents from catalysis by (S)-BINOL-Ti[(O'Pr).sub.2]. The property of BDMAEE to chelate the in situ generated salts Mg[Br.sub.2] inhibits the catalytic activity of the Mg salts, suppresses the unwanted background reaction, and enables the highly enantioselective addition catalyzed by (S)-BINOL-Ti[(O'Pr).sub.2].

An enantioselective method is applied on a readily available and inexpensive trans-cinnamaldehyde compound as a starting material to synthesize [alpha]-methyl carboxylic acids. Dynamic kinetic resolution is applied to allylic alcohol utilizing a ruthenium catalyst and either an (R)-selective lipase or an (S)-selective protease to obtain the corresponding allylic esters in high yield and high ee.

The mechanism of movement of nanovehicles on nonconducting surfaces is elucidated by describing the synthesis and optical properties of five fluorescently tagged nanocars. The molecules are designed such that the arrangement of their molecular axles and p-carborane wheels relative to the chassis is conducive to the control of directionality in the motion of the nanovehicles.

3-Carboxy-2,2,5,5-tetra([super 2][H.sub.3])methyl-1-(3,4,4-[super 2][H.sub.3],1-[super 15]N) pyrrolidinyloxyl is prepared for increasing the sensitivity of [O.sub.2] measurement by EPR imaging. The new isotopically substituted nitroxide has displayed increased sensitivity to changes in [O.sub.2] concentration, which has enabled accurate [O.sub.2] measurement in tissues by using electron paramagnetic resonance imaging.

The intramolecular cyclocarbonylation of substituted 2-(2-iodophenoxy)anilines is catalyzed by Pd[I.sub.2] and 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phospha-adamantane (Cytop 292). A series of substituted dibenzo[b,f][1,4]oxazepin-11 (10H)-ones are prepared under mild reaction conditions.

The effects of the substitution pattern on the photophysical properties of ligands N,N' -bis-((8-hydroxy-7-quinolinyl)methyl)-1,10-diaza-18-crown-6 ether and their metal complexes are examined by developing an efficient microwaves enhanced one-pot Mannich reaction to double-armed diaza-crown ligands carrying a variety of substituents. The new protocol is analyzed by shorter reaction times, enhanced yields and improved product purities with respect to the use of conventional conductive heating.

Thermal Diels-Alder reactions of chiral 9-methoxyethyl and 9-hydroxyethyl anthracene are examined with a range of N-substituted maleimides. Regio- and stereoselective transformations with reducing agents and carbon nucleophiles have shown the synthetic utility of this method, which is applied to the enantioselective synthesis of pyrrole[2,1-a]isoquinolines and the alkaloid crispine A.

Consecutive ring-expansion reactions of oxiranes with dimethylsulfoxonium methylide are analyzed and modeled at the density functional theory (DFT) and second-order Moller-Plesset (MP2) levels of theory by using a polarizable continuum model (PCM) to account for solvent effects. The studies have shown the complete conversion of the enantiomeric purities for the nucleophilic ring expansions of enantiomeric 2-mono- and 2,2-disubstituted epoxides and oxetanes with dimethylsulfoxonium methylide.

The natural p-naphthoquinone (-)-thespesone and its (+)-enantiomer are prepared by bisacylation of a 5-lithiodihydrobenzofuran with 4-methyl-3-tert-butoxycyclobut-3-ene-1,2-dione. (-)-(S)-Thespesone is more efficient against a panel of six cancer cell lines including multiresistant ones than its (+)-enantiomer and also when compared to thymoquinone, a natural antitumoral p-quinone from Nigella sativa.