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Two photocleavable disulfide-bridged tetrapeptides [cyclo(Boc-Cys-Pro-Aib-Cys-OMe) and cyclo(Boc-Cys-Pro-Phe-Cys-OMe)] which provide insight into cyclic peptide dynamics are reported.

Electrodesorption potentials for alkanethiolate self-assembled monolayers (SAMs) on polycrystalline cu and Cu (111) surfaces are determined by using electrochemical techniques combined with Auger electron spectroscopy. For a given alkanethiolate SAM, the electrodesorption peak potentials on polycrystalline Cu and Cu (111) surfaces are found to be similar to each other and are shifted 0.6 and 0.4 V in the negative direction with respect to those found on Au and Ag, respectively.

The efficient total syntheses of gambierol and 16-epi-gambierol is executed in a study on the basis of a convergent strategy. The study demonstrates the power of the methodology, involving the imtramolecular allylation of alpha-chloroacetoxy ether and subsequent ring-closing metathesis, as a practical tool for constructing polycyclic ether frameworks.

An efficient and flexible methodology for the convergent synthesis of polycyclic ethers through intramolecular allylation of alpha-acetoxy ethers followed by ring-closing metathesis is presented. Convergent type syntheses of CDEF ring segment of brevetoxin B and the CDEFG ring segment of gambierol, using esterification reaction for the segment coupling, are described.

Research has been conducted on the acetal thia-cage compounds. The synthesis of these compounds accomplished via direct substitution for the oxygen atom by the sulfur atom in the oxa-cage acetal groups reaction with Lawesson reagent is described.

The total synthesis of the marine ladder toxin (plus or minus)-hemibrevetoxin B is demonstrated using sequential enol ether oxidations, carbon nucleophile additions, and annulations. The methodology employs coupling C-glycoside generation with metathesis or acid-mediated annulation reactions to form fused polyethers.

The development of the chemistry of molecular compounds with Si-P bonds, silylphosphanes, as it evolved in the middle of the century to the present time is discussed. The review focuses on the structure and formation of phosphinophosphinidene phosphoranes, metal cluster compounds, the group of 13/15 semiconductors, and compounds with Si-P and P-C multiple bonds.

Research discusses the application of the title reaction sequences for the syntheses of the (plus or minus)-, (+)-, and (-)-gamma-lycorane, their modifications, and of polycyclic frameworks such as those associated with alkaloids.

The single-crystal X-ray crystallography reveals that the tetraoxa-cages show unusual packing patterns sustained through a network of C--H...O interactions as seen in their solid-state structures. The walls of the cages are made of five- and six-membered rings

A single-step synthetic approach for preparing a new class of furofurans and furopyrroles from propargyl alcohols or amines and arylidene or alkylidene beta-ketosulfones is presented.

Results demonstrate that the round trip radical cyclization reaction leads to highly substituted tricyclo[5.3.1.0(sup)2,6]undecanes from acyclic precursor in a single step. Data indicate that the reaction yields isogymnomitrene and gymnomitrene.

Photoreduction of the alpha-substituted polycylic azoalkanes by primary, secondary and tertiary amines was investigated.

Research was conducted to examine the ambident reactivity (1,2- and 1,4-addition) of phosphazenes IV obtained from triphenylphosphine with hydrogen chloride. Also investigated were the regioselective aza-Wittig reaction (1,2-addition) of phosphazenes IV obtained from diphenylmethylphosphine with aldehydes and the isolation of the corresponding 2-azadiene derivative. Results prove that 2-azadienes can be employed as key intermediates in the synthesis of heterocyclic compounds obtained from beta-amino acids and of polycyclic nitrogen derivatives.

A class of unique amino acid-derived trienes that undergo facile Diels-Alder reactions in the solution phase to yield hydroisoindole derivatives has been studied previously. This was extended to intramolecular Diels-Alder reactions of amino acid derived trienes onto a solid support. Examples were provided which show that furan rings can be employed in solid-phase Diels-Alder reactions to construct libraries of functionalized polycyclic compounds.

The stereochemistry of 1-(3-benzyloxyphenyl)-2-(4-nitrophenyl)ethane was investigated. Bent conformation was found to be such that six-membered ring formation, and not macrocyclization, would occur using the corresponding nitrenium ion. It is proposed that MMX computations may offer a very fast, empirical indicator of which precursors would have a readily accessible conformation that would result in intramolecular cyclization leading to macrocycles being preferred over intermolecular reactions.

Extremely stable carbocations, tris(6-(dimethylamino)- and 6-morpholino-1-azulenyl)methyl, bis(6-(dimethylamino)-1-azulenyl)(4-(dimethylamino)phenyl)methyl and (6-(dimethylamino)-1-azulenyl)bis(4-(dimethylamino)phenyl)methyl cations were produced and their properties were characterized. These cations indicated extremely high stabilities with high pK(sub R)+ values. The extreme stability of these methyl cations is due to the dipolar structure of the azulene rings, in addition to the contribution of the mesomeric effect of three dimethylamino groups.

Research was conducted to examine two new bleomycin analogues whose synthesis, spectroscopy and crystal structures were analyzed. Their Cu(super II) complexes were isolated and characterized by X-ray crystallography. X-ray crystallography showed that the successive replacement of hydrogen atoms by methyl groups on the carbon atoms changed the values of tau from 0.087 to 0.37.

The nickel systems Ni(PPh3)2X2/ZnI2/Zn were studied and observed to have effectively catalyzed cocylotrimerization of internal and terminal alkynes and diynes with alpha, beta-unsaturated cyclic and acyclic enones and alpha, beta-unsaturated lactones. This catalytic reaction provided an efficient method for the construction of tricyclic and bicyclic compounds. The catalysis of an unprecedented linear cotrimerization of an acrylate with two alkynes to afford highly regio- and stereoselective trienes was also observed.

Ruthenium alkylidene was employed as the catalyst in a double ring closing metathesis (RCM) reaction of acyclic tetraenes. This metathesis-based methodology is designed for the construction of bis polycyclic ethers or enol ethers linked by either none, one or two carbons through a double metathesis reaction. RCM reactions of tetraenes with unsaturated ether functions were shown to yield polycyclic unsaturated ethers as major products.

Research was conducted to examine the manifestations of bridgehead-bridgehead interactions in the bicyclo(1.1.1)pentane ring system. The reactions were performed in 5 mm NMR tubes and their progress was monitored by 1H NMR. Results demonstrate that their reactions with xenon difluoride cover a wide range of reactivities. The peak potential data and acidity constants bear significantly on the nature and transmission of substituent electronic effects in the (1.1.1) system.

Research was conducted to examine the synthesis, duplex and triplex forming characteristics of the DNA analogue tricyclo-DNA. A further objective was the thermodynamic investigation of duplex formation of a range of tricyclo-DNA sequences having the nucleobases adenine and thymine. Results suggest that the tricyclo-DNA duplexes are thermodynamically more stable than the corresponding bicyclo-DNA duplexes. They also demonstrated unusual supramolecular association properties and potentially useful biological properties.

A study was conducted to analyze the characterization of the molecular electrostatic potential topography of the pi-regions of 12 polycyclic benzenoid hydrocarbons. The Gaussian94 program was utilized to optimize the molecular systems. Experimental results indicated that the maping of the molecular electrostatic potential promotes an elaborate description of the pi areas. Findings also showed that different aspects of Clar's aromatic sextet theory correlate with the topographical characteristics of the systems.

Fluorescence excitation spectra and fluorescence decays are used to study jet-cooled isolated diastereoisomeric pairs formed between R- and S-2-naphthyl-1-ethanol and a series of optically active terpenes. Results show the presence of chirality-dependent effects in the dynamics of the excited state. The enantioselective quenching of fluorescence of 2-naphthylethanol by R- and S-camphor in n-hexane solution is also due to singlet-singlet electronic energy transfer.

A nonracemic bicyclic lactam was employed to produce a chiral cyclopentane vicinal quaternary carbon centers in optically pure form, which is common to (-)-herbertenediol, (-)-mastigophorene A, and (-)-mastigophorene B. An oxazoline-mediated asymmetric Ullmann coupling was then used to establish chirality about the biaryl axis of mastigophorenes A and B. It was observed that smaller chiral auxiliaries lead to higher levels of atroposelection.

The X-ray structure of (Ru(TTP)(CO)(3'MPyP)) (1) showed that, in the solid state, the two mean porphyrin planes in 1 are canted at an angle of ca. 43 degrees. Diffraction data permitted the refinement of the atomic positional parameters of 1 with the lowest calculated errors among those determined for similar porphyrin adducts. Based on NMR measurements, the solution structure of 1 was found to be very similar to that observed in the solid state though more symmetrical because of the presence of a pseudomirror plane perpendicular to 3'MPyP and going through the 3'N(py) ring.

A new class of chiral C2-symmetric bisferrocenyl diamines, N1,N2-bis((R)-1-ferrocenylethyl)-N1,N2-dimethyl-1,2-ethanediamine (1) and N1,N2-bis((R)-1-((S)-2-(diphenylphosphino))ferrocenylethyl)-N1,N2-dimethyl-1 ,2-ethanediamine (2) were produced. Compound 2 reacts with Ru(DMSO)4Cl2 to produce trans-Ru(2)Cl2, in which the ligand is tetradentate. This complex has catalytic activity toward asymmetric cyclopropanation of some olefins and alkyl diazoacetate, resulting in enantioselectivity of up to 95%.

Research was conducted to examine the synthesis of alkyl-substituted pentaoxa(5)peristylanes through direct chemical transformation of the tetraacetal tetraoxa cages and the ozonolysis of 2,3-bis-endo-7-anti-triacylnobornenes. A three-step efficient sequence was carried out for the preparation of the parent compound. X-ray investigation of the parent compound provided evidence for its structure of pentaoxa(5)peristylanes.

Research was conducted to examine the stereoselectivity in the tethered Biginelli condensation to build the tricyclic guanidine cores of the batzelladine alkaloids. The usefulness of the technique was demonstrated in the synthesis of the dextrorotatory enantiomer of batzelladine B methanolysis product. Results demonstrate that the absolute configuration of the tricyclic portion of batzelladine B is 25aR, 28S,30R.

A new method of creating complex, bicyclic ethers and fused oxethanes from polyalkyl pyran-4-ones has been devised. The process, called the tandem solvent trapping and Norrish type II cyclization, involves the irradiation of the alcohol solvents to produce the complex bicyclic product. The tandem process, which produces up to five contiguous stereocenters with complete selectivity, is recommended for further studies and other possible future applications.

The synthesis of tricyclo[5.2.1.0(super 1.,5)]decane was found to be efficiently performed through the intramolecular double Michael reaction of 5-(5-methoxycarbonyl-4-pentenyl)-2-cyclopenten-1-one. Highly stereocontrolled total syntheses of (+/-)-8,14-cedranediol (2) and (+/-)-8,14-cedranoxide (1) were conducted by the use of the said technique. Heating 5-(1,5-dimethyl-5-ethoxycarbonylpent-4-enyl)-2-cyclopenten-1-one with TMSCl, Et3N and ZnCl2 in o-dichlorobenzene at 150 deg C afforded (+/-)-(1R*,2R*,5R*,6R*,7S*)-2,6-dimethyl-6-ethoxycarbonyltricyclo[5.2.1.0(su per 1,5)]decan-9-one (16) as a single isomer. The product 16 was stereoselectively transformed to cedranoids 2 and 1.

Regioselective syntheses of 2,6-diazabicyclo[3.2.x]alkan-3-ones (x = 1-3) (34) were conducted through the insertion of nitrogen next to the bridgehead of 2-azabicyclo[2.2.x]alkanones (32) with hydroxylamine-O-sulfonic acid. The ketones 32 under Schmidt reaction conditions (HN3/H2SO4) produced not only large quantities of bridgehead migrated lactams 34, but also, when x = 2 or 3, the methylene (M) migrated lactams, 3,6-diazabicyclo[3.2.x]alkan-2-ones.

Bioassay-directed fractionation of the ethanol extracts of two Amphimedon spp. gathered from the Great Australian Bight afforded four new macrocyclic lactone/lactams, amphilactams A-D. The amphilactams were found to be powerful nematocides and their structures were assigned using detailed spectroscopic analysis and comparison with synthetic model compounds. The amphilactams have both carbon skeletons and an enamino lactone/lactam moiety never before seen in previous studies on natural products.

The 5-endo-trig radical cyclization of bromomethyldimethylsilyl ethers was investigated. The objective was to determine whether the intermediate radical originating from the 5-endo-trig ring closure could be trapped in a 6-exo-dig fashion. Experimental results showed that an efficient radical cascade involving the 5-exo-dig, a 6-endo-trig, a 4-exo-dig, a 1,6-H transfer and another 1,6-H transfer leads to the diastereoselective synthesis of bicyclo(3.1.1)heptanes. Furthermore, the diastereoselectivity of the 6-endo-trig step is regulated by the size of the R substituent at the propargylic position.

The guest-host stoichiometry of the anion complex of H2PO4- and F- selective uranyl salophene derivatives was found to be 2:1 in PVC/NPOE ion-selective membranes of potentiometric sensors. This stoichiometry is different from the stoichiometry observed in DMSO solution or solid state. However, the 2:1 stoichiometry, similar to that in PVC/NPOE membrane matrix, was also seen in 1H NMR spectroscopy of nonpolar solvents such as chloroform.

The translational isomerism which is experimentally seen in some [2]rotaxanes was investigated and modelled through molecular mechanics and molecular dynamics computations applying Allinger's MM3 force field and MM3*, the implemented version of MM3 for MacroModel. Results showed accetable agreements between the calculated and experimental values for translational barriers. Translational barriers were caused by nonbonded interactions and can be tuned by introducing alkyl groups in the polyether chain.

A study was conducted to characterize the preparation of diacetal trioxa-cage compounds supporting a novel type of skeleton and to compare the reactivity pattern of the compounds with their heterologues. Results indicated that a novel type of diacetal trioxa-cage compounds can be synthesized in good yields using a short sequence. Findings also showed that carbon atoms at the bridge of the diols the formation of the trioxa-cage skeleton.

Two new homoleptic copper(I) pyrazolate complexes, the trinuclear (Cu(dmnpz))3 and the tetranuclear anionic (Cu4(dmanpz)6)2- species were synthesized and their structures determined. An examination of their reactivity showed that both complexes readily react with cyclohexyl isocyanide, giving the dinuclear complexes (Cu(dmnpz)(RNC))2 and (Cu(dmnpz)(RNC)2)2, and with PPh3 to afford the dimeric derivative (Cu(dmnpz)(OOh3))2.

A tetrahedral arrangement of four six-coordinate Ni(super II) ions centered on the fifth comprises the structure of the pentanuclear clusters (Ni5(OH)(bta)5(acac)4(H2O)4) and (Ni5(OH)(5,6diMebta)5(acac)4(H2O)4). Antiferromagnetic interactions between the metal ions within the clusters were observed from variable-temperature magnetic susceptibility data. Both complexes display an intermediate ground state, with the spin value of the ground state apparently increasing when the symmetry of the cluster increases.

Samarium(II) iodide was used to facilitate a tandem intermolecular carbonyl addition/intramolecular nucleophilic acyl substitution sequence, producing seven- through nine-membered monocyclic, bicyclic and tricyclic systems with good yields and high diastereoselectivities. Such a tandem reaction is made up of an intermolecular reaction followed by an intramolecular ring expansion which results in a formal (m + n) cycloaddition, beginning from extremely simple, readily available substrates.

A ruthenium alkylidene compound ca be used to catalyze polycyclization reactions. The reaction is an efficient, catalytic procedure for the production of polycyclic molecules from acyclic precursors. The reaction occurs through a cascade of metathesis steps with either acetylenic or cycloalkenyl relay units. Several structural types are accessible depending on the topology of the precursor and relay unit used.

Four unsymmetrical covalently linked porphyrin dimers were synthesized and their electrochemical, spectroelectrochemical and/or photophysical characteristics were investigated. Computed energy transfer rate constants were observed to be consistent with the empirical data and indicated that the energy transfer mechanisms are best represented by a Foster process. Highly efficient and directional energy transfer processes were observed.

Areneruthenium chemistry was employed to produce intramolecular S(sub N)Ar reactions between phenoxide nucleophiles and chlorophenylalanine resides that are linked by a peptide chain, resulting into the formation of a bicyclic peptido aryl ether system. This ether system corresponded to the BCDF system of the glycopeptide antibiotics ristocetin A and teicoplanin. A simple and selective base-catalyzed complete inversion of configuration at the D ring arylglycine residue was found when this unit is the carboxylate terminus on a 16-membered ring system corresponding to the DEF rings of the target molecules.

The interaction of easily available macrocyclic bis(carbodiimides) with nitrogen reagents such as ammonia, primary or secondary alkylamines and alpha,omega-diamino compounds was observed to result into a unique group of macrocyclic bis(guanidines). The macrocyclic bis(guanidines) were isolated as crystalline solids in high yields. The crystal and molecular structure of the bis(guanidine) produced from bicyclo(8.8.2)docosane was obtained.

The behavior of bicyclic dithioether dication reactions with alkynes and alkenes are observed in an experiment. This dithioether dication features a 1,4-dithiane 1-oxide with a carbon-carbon multiple bond. Results show that the corresponding sulfonium salts are formed by the reaction. The reaction, which is affected by steric and electronic factors, does not affect the arrangement of substituents at the double bond of the original alkene.

Hemiporphyrazines are four-unit macrocycles which contain two opposite-faced units and two other hetero-aromatic moeities which are bound through aza bridges. These compounds are considered building blocks of molecular materials. Because of their high synthetic versatility, the compounds' physical properties such as electrical and optical can be easily analyzed. The compounds can also be utilized in the preparation of two-dimensional metal with potential electrical and magnetic properties.

A study was conducted where ab initio calculations of the energies of the ground state tautomeric forms of hypericin nd its derivatives to determine to what degree do they contribute to the ground state heterogeneity. The most important result of the calculations performed in the study is that only the normal tautomeric form of hypericin is significantly populated in the ground state, at room temperature, but it is possible that other tautomers could be stabilized by particular solvents.

The steady-state and time-resolved fluorescence anisotropies of hypericin, hypocrellin and five other model compounds were investigated. The steady-state excitation anisotropies for each of the analogues have an extensive minimum at -400 nm with a negative value. The value of the anisotropy is positive at the blue and red edges of the spectrum. The limiting anisotropies were found to be consistent with the corresponding steady-state values.

The chemo-, regio-, and stereocontrolled methodology for the simple and efficient synthesis of a large variety of cis-decalins and related fused polycyclic systems is presented. Observations show that the first ring-opening reaction is significantly faster than the second which permits the sequential transformation of the oxabicyclic moieties. Results also demonstrate the flexibility of the sequential ring-opening process and its limitations while a novel enantioselective mode of opening is presented.

Macrocyclic 'cholaphanes' are prepared from steroid cholic acid. These have large cavities with inward-directed hydroxyl groups which may be used for binding polar molecules such as carbohydrates in nonpolar media. New characteristics are the externally directed alkyl chains which improve solubility in organic solvents and reduce conformational freedom due to the truncation of the steroidal side-chain. The smallest macrocycle has very little flexibility, favoring an open conformation which is also seen in the X-ray crystal structure of its pentahydrate.