(±)-Fenvaleric acid 2, the key intermediate for the preparation of the pesticide esfenvalerate 1, was prepared by a novel sequence which first involves the Henry reaction of 2-methyl-1-nitropropane and 4-chlorobenzaldehyde. The nitroaldol reaction provided nitroalcohol 5 which was then reduced to the corresponding aminoalcohol 6. Submission of 6 to an aminopinacol rearrangement promoted by nitrous acid deamination then afforded aldehyde 8 through a 1,2-aryl shift. The product fenvaleric aldehyde 8 was then converted to the title compound 2 by a modified Jones oxidation.
Phenazine and the dicarboxylic acids fumaric-, 2,3- dihydroxyfumaric-, and oxalic acid form 1 : 1 cocrystals. X-ray analysis shows that the molecules are arranged as linear tapes, mainly held together by strong O-H…︁N and weak C(sp 2)-H…︁O hydrogen bonds. Individual molecules form staples which are surrounded by staples of the other molecules. The angle between neighbouring tapes varies from ca. 90° in the cocrystal of phenazine and fumaric acid to ca. 70° in the co-crystal of phenazine and 2,3-dihydroxyfumaric acid, and ca. 25° in the cocrystal of phenazine and oxalic acid. The molecules assume an offset face-to-face arrangement in individual phenazine staples. Negligible π-stacking is observed in the cocrystals of phenazine with fumaric- and 2,3-dihydroxyfumaric acid. The absence of the CC double bond as spacer in oxalic acid leads to appreciable π-overlap of phenazine molecules in the cocrystal. As a consequence, the latter cocrystal displays special properties. An irreversible lightinduced electron transfer generates initially singlet and triplet biradicals with the unpaired electrons positioned on neighbouring phenazine molecules. Partially, the electrons are transformed to magnetically independent electrons which show strong exchange narrowing in the e.p.r. spectrum at temperatures > 0 °C. The proposed model is supported by UV/Vis-e. s.r.-, and SQUID measurements.
Somatostatin octapeptide analogues of the general sequence DPhe5-Phe 6-Tyr7-DTrp8-Lys9-Val10-Ph 11-Thr12-NH2 containing two types of backbone cyclization have been synthesized by the solid phase methodology. Backbone cyclization in these peptides was achieved via N-modified phenylalanines in position 6 and 11. The N-modified amino acids were incorporated as dipeptide building units which have been prepared in solution prior to the solid phase synthesis. Two dipeptide units of structure a) Fmoc-aa 1 ψ[CO—N((CH2)n-X)]Phe—OH or b) Fmoc-aa1 ψ[CH2—N(COlpar;CH2)n-X)]Phe—OH have been introduced into the peptide sequence. Different resins and linkers were examined for an optimized peptide assembly and monitoring. The synthesized somatostatin analogues are highly resistant against enzymatic degradation as determined in vitro by incubation with rat liver homogenate. The biological activity was determined in binding experiments to the somatostatin receptors expressed in CHO- or BON-1 cells. Most analogues show moderate activity without differentiation between the receptor subtypes.
We introduce a systematic nomenclature for mechanically linked molecules - such as catenanes, rotaxanes, and assemblies derived from these structural elements - which comes up to the increasing complexity of already synthesized interlocked molecules and the ones to be expected in future. Like in the naming of other substance classes (polycycles, phanes, crown compounds, podands, dendrimers) we attach importance to the fact, that certain units in the name, e.g. expressions in brackets, quickly convey an idea of the molecular architecture. Furthermore, this modular nomenclature reveals as many analogies to the IUPAC nomenclature as possible.
A convenient method for the synthesis of the title compounds 4a,b, 3a,b via an intramolecular condensation of thiourethanes, derived from the acylation of enantioenriched α-thio benzyllithium compounds, is reported. The structure of one of the major diastereomers was elucidated by a singlecrystal X-ray analysis and compared to semiempirical calculations.
Systematical investigation of solvent-free oxidations of organic model compounds with potassium permanganate on inorganic carriers leads to conclusion, that mechanochemical stimulation can induce oxidations. In case of the benzyl-type arenes these conversions are selective at good yields. Olefines react to carbonic acids. The presence of water enhances the yield of almost all educts.
The photopolymerization of 1,2-epoxy-6-(9-carbazolyl)- 4-oxahexane (ECOH) initiated with dual function sulfonium salt bis [4(diphenylsulfonio)-phenyl] sulfide-bishexafluoroantimonate (Cyracure ® UVI 6974) and ( η5-2,4-cyclopentadien- 1-yl) [(1,2,3,4,5,6-η)-(1-methylethyl)benzene]-iron (+)-hexafluorophosphate (—1) (Irgacure ® 261) has been studied. Higher rate constant values and degrees of polymerization are established for the ECOH photopolymerization initiated with Cyracure ® compared with those obtained using Irgacure ® . The influence of temperature on the rate of ECOH photopolymerization, molecular weight and conversion limit is discussed. The activation energy for the photopolymerization of ECOH with the sulfonium salt has been established.
Model studies on the transformation of the olefinic unit contained in n-pentenyl glycosides (NPGs) to glycoamino acids is described. The methodology involves a Horner-Emmons olefination with a protected glycine derived phosphonate, followed by asymmetric hydrogenation using Du-PHOS catalyst system. A variety of protecting group schemes have been investigated and their stereoselectivity in the hydrogenation reaction determined. With N-Boc and C-TSE ester protection, the diastereoselectivity in the reaction was measured by 1H NMR analysis with “racemic” product as a comparison. These modified glycoamino acids are also useful for peptide synthesis. The methodology appears to be general and was extended to include the synthesis a glycoamino acid containing the complex hexasaccharide Globo-H.
The title compounds were prepared in a multi-step synthesis in which primarily the pyrene building blocks were formed (1,2 → 11a,b). The final reaction step 11a,b → 12a,b consisted of a threefold trans selective cyclocondensation process that generated the central 18-membered ring. Hexyloxy or dodecyloxy sidechains attached on the periphery led to the formation of liquid crystalline phases.
The utility of high pressure for the understanding of chemical reactions and its application in organic synthesis is shown for cycloadditions (inter- and intramolecular Diels-Alder reactions, 1,3-dipolar and [2+2] cycloadditions), cheletropic reactions and pericyclic rearrangements (Cope and Claisen rearrangements and electrocyclizations). The origin of the effect of pressure on chemical reactions is discussed. Especially, the change in the packing coefficient during cyclization of chains and the effect of electrostriction on reactions, in which charged species are generated, contribute substantially to a volume contraction leading to a powerful pressure-induced acceleration of such reactions. Finally, the effect of pressure on free-radical reactions (homolytic bond dissociations and quinone oxidations) is described.
Cyanuric fluoride (2) is one of the most popular fluorinating agents in organic chemistry. The title compound could be prepared in a 50 to 100 g scale by means of a chlorine fluorine exchange, the process was characterized by a simple preparation procedure, cheap reactants and a low time exposure. Carboxylic acids were converted into the corresponding acid fluorides 4a-g using cyanuric fluoride. A nonaqueous work-up led to high yields on synthesizing a range of functionalized acid fluorides.
We report the synthesis of a series of new hydrocarbon macrocycles. Following the dithia-phane route, four large rings 3-6 of the cyclophane type containing different numbers of ring atoms were prepared confirming the general applicability of this route compared to alternative macrocyclizations. Cycle 3 is the hydrocarbon analogue to the tetra-lactam and the sulfone amide macrocycles 1 and 2 used in many rotaxane syntheses. The macrocycles synthesized here are supposed to be uselful as wheels in the slippingapproach to rotaxanes to further establish a reference system for the cavity size of cyclic compounds by comparing them to certain complemenatry blocking groups. The x-ray data obtained of the macrocycles 3, 5, and 6 reveal the cavity shape and size in solid state.
A series of N-formyl-O-acyl-β-phenylserine derivatives 1b-7b were prepared by the interaction of N-acyl-b-phenylserine ethyl esters 1a-7a with formic acid in presence of 1.5% HF. One-pot acyl group N → O migration followed N-formylation under elaborated reaction conditions. The kinetics of the reaction was investigated. The carboxylic acid moiety in the structure of β-phenylserine had a strong influence on the reproduction of the used test-viruses. The toxicity and antiviral activity is dependent on the diastereomeric forms of evaluated compounds.
From mistletoe extracts, a chitin-binding lectin (cbML) was isolated and its primary structure determined. The protein is composed of two identical protein chains, linked by am interchenary disulfide bond. Each chain is characterized by four intrachenary disulfide bridges. The structure shows high homology to hevein, one of the prominent allergens of natural rubber latex. cbML could also be detected in commercially available pharmaceutical mistletoe extract preparations. The described isolation procedure and characterization allows isolation of cbML in highly pure form and sufficient quantities, now ready for unequivocal determination for its pharmacological effects.
Reaction of benzenediazonium chloride with active [1,2,4]triazin-3-ylthio-methylene compounds 3 afforded the azo coupling products 5, which yielded [1,2,4]triazolo[4,3-b][1,2,4]triazin-7(1H)-ones 8 upon treatment with sodium ethoxide in ethanol. The latter products 8 were characterized on the basis of alternate synthesis and spectral data. The mechanism of formation of 8 and the regiochemistry of the studied reactions are discussed.
The synthesis of tetrahydro-2,1-benzisothiazolium salts 8 and cyclohepta[c] isothiazolium salts 11 by ring transformation of bicyclic isothiazolium perchlorates 2, 3 is described and the by-products 9, 10 and 12 are characterized. Oxidation of the bicyclic salts 8 and 11 results in a new route to obtain ω-(2-aryl-1,1,3-trioxo-2,3-dihydro-1H-isothiazol-4-yl)-alkanoic acids 17 and 18 by Criegee-type-rearrangement.
Michael reactions of β-keto esters 1a—1h with methyl vinyl ketone (2a) catalyzed by FeCl3 · 6 H2O (5 mol%) proceed with up to 99% yield. Conversion of β-keto esters 1a—1e derived from chiral alcohols with 2a result in only very low diastereoselectivities (max. de 20%). A bis-β-keto ester 1i and a bis-vinyl ketone 2b — both valuable monomers for poly-Michael reactions — are synthesized from common starting materials in up to gram quantities.
Recent sol-gel techniques enable bioactive composite layers to be prepared by the embedding of bioactive compounds, biomolecules (BMs) and cellular systems within inorganic layers. These novel bioactive layers offer interesting new applications, e.g. biocompatible coatings on im plants and medical products, the preparation of biosensors and biocatalysts, and coatings that can release biocides in a controlled manner.
The preparation of novel acetic acid derivatives of pyrazole 3a,b and pyrimidine 2a-e is achieved by condensation of dimethyl acetylsuccinate (1) with appropriate reaction partners. Also triethyl 1,1,2-ethanetricarboxylate (6) is a valuable starting material, which is demonstrated by the synthesis of previously unknown pyrimidin-5-yl acetates.
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