Total Synthesis of Cyclothialidine

A total synthesis of cyclothialidine ( 1 ), a new DNA gyrase inhibitor isolated from Streptomyces filipinensis, is described. The synthetic concept was tested by preparing the lactone 13 (Scheme 2) which contains the characteristic bicyclic core entity of 1 . Key features of the synthesis of 1 are: preparation of 3,5-dihydroxy-2,6-dimethylbenzoic acid ( 23 ) from 3,5-dihydroxybenzoic acid ( 19 ) by two consecutive Mannich aminomethylation/hydrogenation sequences; benzylic N-bromosuccinimide bromination of an ester derivative 25 thereof and its subsequent coupling with Boc-Ser-Cys-OMe ( 11 ); cyclization of the ω-hydroxy acid 29 29 to the 12-membered lactone 30 using preferably Mitsunobu conditions; completion of the peptidic side chains of 1 using Boc strategy (Scheme 4). Optically pure cis-N-(tert-butoxycarbonyl)-3-hydroxy-L -proline ((–)- 14 ) was obtained by resolution of the racemate via an efficient reaction sequence containing a lipase-catalyzed enantiospecific acetate hydrolysis (Scheme 3). The structure of natural 1 was confirmed by comparison with the synthetic material. The synthetic route described provides also easy access to analogues of 1 , e.g., via the intermediate 30 .     

Fluorescent properties of oligonucleotide-conjugated thiazole orange probes

The fluorescence properties of thiazole orange, linked via a (1) hydrophobic alkyl or a (2) hydrophilic ethylene glycol chain to the central internucleotidic phosphate group of a pentadeca-2'-deoxyriboadenylate (dA15), are evaluated. Linkage at the phosphate group yields two stereoisomers, S-isomer of the phosphorus chiral center (Sp) and R-isomer of the phosphorus chiral center (Rp); these are studied separately. The character of the linkage chain and the chirality of the internucleotidic phosphate linkage site influence the fluorescent properties of these thiazole orange-oligonucleotide conjugates (TO-probes). Quantum yields of fluorescence (phifl) of between 0.04 and 0.07 were determined for the single-stranded conjugates. The fluorescence yield increased by up to five times upon hybridization with the complementary sequence (d5'[CACT15CAC3']); (phifl values of between 0.06-0.35 were determined for the double-stranded conjugates. The phifl value (0.17) of thiazole orange, 1-(N,N'-trimethylaminopropyl)-4-[3-methyl-2,3-dihydro-(benzo-1,3-thiazole)-2-methylidene]-quinolinium iodide (TO-Pro 1) in the presence of the oligonucleotide duplex (TO-Pro 1: dA15.d5'[CACT15CAC3'] (1:1)) is much less than that for some of the hybrids of the conjugates. Our studies, using steady-state and time-resolved fluorescence experiments, show that a number of discrete fluorescent association species between the thiazole orange and the helix are formed. Time-resolved studies on the four double-stranded TO-probes revealed that the fluorescent oligonucleotide-thiazole orange complexes are common, only the distribution of the species varies with the character of the chain and the chirality at the internucleotidic phosphate site. Those TO-probes in which the isomeric structure of the phosphate-chain linkage is Rp, and therefore such that the fluorophore is directed toward the minor groove, have higher phifl values than the Sp isomer. Of the systems studied, thiazole orange linked by an alkyl chain to the internucleotidic phosphate (Rp isomer) has the highest phifl and the greatest fraction of the longest-lived fluorescent thiazole orange species (in the hybrid form).     

Rhodium(II)‐Catalyzed Inter‐ and Intramolecular Cyclopropanations with Diazo Compounds and Phenyliodonium Ylides: Synthesis and Chiral Analysis

Different classes of cyclopropanes derived from Meldrum's acid (=2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione; 4 ), dimethyl malonate ( 5 ), 2‐diazo‐3‐(silyloxy)but‐3‐enoate 16 , 2‐diazo‐3,3,3‐trifluoropropanoate 18 , diazo(triethylsilyl)acetate 24a , and diazo(dimethylphenylsilyl)acetate 24b were prepared via dirhodium(II)‐catalyzed intermolecular cyclopropanation of a set of olefins 3 (Schemes 1 and 4–6). The reactions proceeded with either diazo‐free phenyliodonium ylides or diazo compounds affording the desired cyclopropane derivatives in either racemic or enantiomer‐enriched forms. The intramolecular cyclopropanation of allyl diazo(triethylsilyl)acetates 28, 30 , and 33 were carried out in the presence of the chiral dirhodium(II) catalyst [Rh₂{(S)‐nttl)₄}] ( 9 ) in toluene to afford the corresponding cyclopropane derivatives 29, 31 and 34 with up to 37% ee (Scheme 7). An efficient enantioselective chiral separation method based on enantioselective GC and HPLC was developed. The method provides information about the chemical yields of the cyclopropane derivatives, enantioselectivity, substrate specifity, and catalytic activity of the chiral catalysts used in the inter‐ and intramolecular cyclopropanation reactions and avoids time‐consuming workup procedures.     

Study of polymer treatment with tetrafluoromethane plasma: Reactivity of fluorinated species on model surfaces

Polyolefins and their model molecules, some n-alcanes, have been modified by a tetrafluoromethane microwave plasma. The chosen molecules are high-density polyethylene (HDPE) and hexatriacontane (HTC), low-density polyethylene (LDPE) and paraffin, and polycaprolactone (PCL) and octadecyl octadecanoate (ODO). It has been found, except for paraffin, that the model surfaces have the same behavior as the corresponding polymers. Plasma modification is described as the sum of two mechanisms: degradation and fluorination. These reactions seem to be competitive and parallel. Degradation and fluorination rates are dependent on treatment time and are practically independent on substrate position. A domain of fluorination exists near the edge of plasma, whatever the substrate in or outside plasma. © 1993 John Wiley & Sons, Inc.     

[Mo12O40P][C44H38P2][CoC10H10] * 3(C3H7NO): A quasi-ternary intercluster compound

Binary intercluster compounds (IC) can be reduced to basic structure types of ionic solids. We examined the validity of this concept for ternary compounds, on the example of a quasi-ternary intercluster compound made from a Keggin anion ([PMo₁₂O₄₀]^3?), an organic cation (o-xylylenebis(triphenylphosphonium)), and a complex (cobaltocenium). The new compound and its two related quasi-binary IC were investigated by X-ray diffractometry, examined for intermolecular interactions such as hydrogen-bonding, π–, or van der Waals-interactions, and evaluated for possible reductions to basic structure types.     

Application of Prins cyclization to the total synthesis of (+)-decytospolides A and B

(+)-Decytospolides A and B, natural products containing the tetrahydropyran skeleton, were synthesized via Prins cyclization as the key step.     

Phosphorus Containing Tri-and Hexamacrocycles

Abstract

Multisite receptors containing more than two macrocyclic cavities. despite of the fact that their syntheses, most often, require sophisticated pathways, arc of very high interest since they may allow new insights into ion channel transfer, ion conduction.[1] We report here a method which combine simple reactions, high yields (80%), with easily prepared starting reagents[2], of two new polymacrocyclic system, a tri-(r) and an hexamacrocyck(II). They were obtained by a condensation reaction between 4-formylbenzo-15-crown-5 (3 or 6 quiv, respectively) and phosphouihydrazide (1 equiv.) or hexahydrazide (1 equiv.) in tetrahydrofuran.     

Raman spectroscopy and thermal analysis of gum and silica-filled NR/SBR blends prepared from latex system

Natural rubber/styrene-butadiene rubber (NR/SBR) blends, with and without silica, were prepared by co-coagulating the mixture of rubber latices and various amounts of well-dispersed silica suspension. An attempt to predict blend compositions was made using Raman spectroscopy in association with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It was found that the intensity of each Raman characteristic peak was strongly dependent on the blend composition, but there was no significant evolution with the presence of silica. Also, TGA results revealed an improvement in thermal stability of NR/SBR blends with increasing both SBR and silica contents due to the dilution effect. Two distinct glass transition temperatures (T_g) were observed in DSC thermograms of all blends, and their T_g values were independent on both blend composition and silica content. This indicated a physical blend formation, which agreed well with no shifts in Raman peaks of the blends in comparison with those of the individual rubbers. Linear regression with R² quality factor close to 0.99 was achieved when plotting intensity ratio at 1371/1302 cm^?1 versus blend ratios. On the other hand, the peak height ratio and heat capacity ratio from TGA and DSC analysis, respectively, yielded quadratic equations as a function of blend ratios.     

Derivatives of 3-Deoxy-3-(N-Hydroxyamino)-D-Ribose

Abstract

A series of 3-(N-arylmethyl-N-hydroxyamino)-l,2-O-cyclopentylidene-3-deoxy-5-O-toluoyl-α-D-riboses has been prepared. The blocking groups used were chosen to allow an easy nucleosidation of these compounds to spin labelled analogs of natural nucleosides. The conformational behavior of the N-arylmethyl-N-hydroxyamino group has been studied using ³/_CH NMR coupling data and molecular mechanics computations. Upon spontaneous oxidation, these hydroxylamines led to the corresponding aminoxyl free radicals which were submitted to EPR spectroscopy and quantum mechanical computations at a semiempirical level (PM3).