Absolute Configuration of Gilmaniellin

The absolute configuration of dechlorogilmaniellin ( 2 ) could be determined from its chiroptical data by applying coupled-oscillator theory to the CD couplet around 272 nm and from the sign of its n →π^* Cotton effect. Gilmaniellin ( 1 ) has the same absolute configuration.     

Microbiological transformion of bicyclic monoterpenes by Absidia orchidis (Vuill.) Hagem. I. Reduction of camphorquinone and isofenchonequinone. 17. Section on reactions with microorganisms

(—)-Camphorquinone ( 1a ) was transformed to a mixture consisting of 3-endo-hydroxy-camphor ( 2a ) (40%), 3-exo-hydroxy-camphor ( 3a ) (30%) and 2-endo-hydroxy-epicamphor ( 4a ) (30%) by an aqueous suspension of the mycelium of Absidia orchidis (Vuill.) Hagem. The composition of the reduction products was determined by the NMR. spectra. Incubation of the enantiomeric (+)-camphorquinone ( 1b ) under the same condition yielded 3-exohydroxy-camphor ( 3b ) as single product. Since both substrates form their products immediately and in the same ratio the possibility of a posterior isomerization of 3a yielding the ketols 2a and 4a can be ruled out. For comparison the course of the chemical reduction of camphorquinone ( 1 ) to the ketols (Zn in acetic acid, hydrogenation with Raney -Ni as catalyst, NaBH₄) was investigated. Camphor was not transformed by Absidia orchidis. (—)-Isofenchonequinone ( 6a ) yielded upon incubation with an aqueous suspension of the mycelium of Absidia orchidis exclusively 2-endo-hydroxy-epi-isofenchone ( 7a ). The enantiomer diketone 6b gave the same result, i. e. the ketol 7b as the only transformation product. Also with isofenchonequinone the chemical reduction to the ketols by Zn in acetic acid, hydrogenation with Raney -Ni as catalyst and NaBH₄ was studied.     

Asymmetric synthesis of α-hydroxy-esters via ester enolates

3-Phenylpropionates of chiral alcohols derived from (+)-camphor are oxidized by Mo0₅· Py·HMPT (MoOPH) with high diastereoselectivity.     

Selektive Reaktionen an Cytochalasin D

In connection with the total synthesis of cytochalasans the cleavage of the macrocyclic system of cytochalasin D ( 3 ) was studied in order to gain useful relay compounds. Selective scission of the double bond in 19-position was achieved by controlled ozonolysis leading to compound 7 (Scheme 1). Treatment of 3 with OsO₄ and subsequent acetylation gave the tetraacetoxy- and diacetoxy derivatives 8 and 9 , respectively. Sharpless epoxidation of 3 yielded the mono-, di- and the two epimeric triepoxides 10 , 11 , 12 , and 13 , respectively. Further studies concerned the isomerization of the 6(12)-double bond to 6(7)-double bond by an allylic rearrangement. Treatment of 3 with mesylchloride and triethylamine led to 12-hydroxy-, 12-mesyloxy- and 12-chlorozygosporin ( 14 , 16 , and 17 , resp.) (see Scheme 2). Epoxidation of 14 gave a mixture of the two epimeric 6,7-epoxides 21 and 23. Zn-reduction of 18 (the corresponding bromide of 17 ) led to zygosporin G ( 20 ). In order to convert a carbocyclic cytochalasan into a macrocyclic derivative, 3 was converted to 32 (Scheme 2). Treatment of 32 with H₂O₂ in acetic acid/chloroform or with phenylselenylperacid/H₂O₂ yielded the enollactone 33 . Finally, 17,18-secocytochalasin D derivatives were prepared for the synthesis of unnatural analogs of macrolidic cytochalasans. The diol 26 was converted into the ketoaldehydes 38 and 40 and to the corresponding keto-acids 43 and 44 (Scheme 3), which were reduced to the ω-hydroxycarboxylic acids 45 – 48. Treatment of 47 with 2,2^/-dipyridyldisulfide/triphenylphosphine/xylene gave probably the lactone 50 .     

Approaches to the synthesis of cytochalasans. Part 10. Cuprates as reagents for the formation of C?C bonds

Based upon our novel concept for the total synthesis of cytochalasans, the model lactams 2–9 were treated with Bu₂Cu(CN)Li₂. The results of these conversions vary much from those obtained with Ph₂Cu(CN)Li₂, demonstrating the uncertainty of predictions in cuprate chemistry. The bicyclic compound 20 was prepared in good yield. However, all attempts to convert p-toluenesulfonate 20 into the Ph-substituted derivative 21 , an intermediate for the synthesis of cyiochulusm B(1) , have failed so far.     

1H- und 13C-NMR.-Spektroskopie der Nonadride

¹H- and ¹³C-NMR. Spectroscopy of the Nonadrides The ¹H- and ¹³C-NMR. spectra of the nonadrides glaucanic acid ( 1 ), glauconic acid ( 2 ), heveadride ( 3 ), byssochlamic acid ( 4 ), scytalidin ( 5 ), rubratoxin A ( 6 ), and rubratoxin B ( 7 ) have been measured. Partial decoupling experiments permitted assignment of the majority of the signals.     

N‐Heterocyclic carbenes derived from imidazo‐[1,5‐a]pyridines related to natural products: synthesis,structure and potential biological activity of some corresponding gold(I) and silver(I) complexes

A series of Au(I) complexes ( 12 , 13 , 14 , 15 , 16 ) and Ag(I) complexes ( 17 , 18 , 19 , 20 ) derived from imidazo[1,5‐a]pyridin‐3‐ylidenes were synthesized from AuCl(SMe₂) or by reacting silver(I) acetate with 2,5‐dimethylimidazo[1,5‐a]pyridin‐2‐ium iodide or imidazo[1,5‐a]pyridin‐2‐ium salts, and were characterized using NMR spectroscopy, mass spectrometry and elemental analyses. In addition, the Au(I) complex 13 and the Ag(I) complex 19 were characterized using single‐crystal X‐ray diffraction. Using paclitaxel as a standard, all Au(I) and Ag(I) N‐heterocyclic carbene complexes were evaluated for their in vitro anti‐tumour activity against 12 cell lines using a monolayer cell survival and proliferation assay. The highest anticancer activity was found for complexes 15 , 13 and 14 with mean IC₅₀ values of 10.09, 10.42 and 12.28 μM, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Dispersive waves in microstructured solids

The wave motion in micromorphic microstructured solids is studied. The mathematical model is based on ideas of Mindlin and governing equations are derived by making use of the Euler–Lagrange formalism. The same result is obtained by means of the internal variables approach. Actually such a model describes internal fields in microstructured solids under external loading and the interaction of these fields results in various physical effects. The emphasis of the paper is on dispersion analysis and wave profiles generated by initial or boundary conditions in a one-dimensional case.     

Trifluoromethyl Derivatives of Elusive Fullerene C98

Data concerning the isomeric composition of C₉₈ and the chemistry of C₉₈ derivatives are scarce due to very low abundance of C₉₈ in the fullerene soot. Trifluoromethylation of C₉₈-containing mixtures followed by HPLC separation of CF₃ derivatives and single crystal X-ray diffraction study resulted in structural characterization of four compounds C₉₈(248)(CF₃)_18/20, C₉₈(116)(CF₃)₁₈, and C₉₈(120)(CF₃)₂₀. To date, these compounds represent the largest fullerenes isolated as CF₃ derivatives with experimentally determined molecular structures. The addition patterns of C₉₈(CF₃)_18/20 are discussed in detail revealing the stabilizing factors, such as isolated double C=C bonds and benzenoid rings on C₉₈ fullerene cages. A detailed comparison with the addition patterns of the known C₉₈Cl_n allowed us to contribute to the better understanding the chemistry of elusive C₉₈ fullerene.     

Addition of perfluoroalkanoic acids to (R)-(+)-limonene

Perfluoroalkanoic acids with different lengths of the perfluoroalkyl radical selectively add under mild conditions to the exocyclic double C=C of limonene to give the corresponding Markovnikov adducts, α-terpinyl perfluoroalkanoates. The reaction in the presence of sulfuric acid 0°C involves both double C=C bonds in the limonene molecule with formation of p-menthane-1,8-diyl bis(perfluoroalkanoates).