1H- und 13C-NMR.-spektroskopische Untersuchungen an den vier diastereomeren (±)-Dihydropalustraminsäure-methylestern; Strukturkorrelation mit (−)-Dihydropalustraminsäure-methylester sowie mit dem Alkaloid Palustrin. 14. Mitteilung über Schachtelhalmalkaloide

¹H-and¹³C-NMR. spectra of methyl esters of the diastereomeric (±)-dihydropalustramic acids; structural correlation of (?)-dihydropalustramic acid with the alkaloid palustrin Unambiguous assignment of cis-trans configuration at the piperidine ring of the four diastereomeric methyl esters of the (±)-dihydropalustramic acids is based on the interpretation of ¹H- and ¹³C-NMR. data. (?)-Dihydropalustramic acid, the important degradation product of the alkaloid palustrin is shown to be threo-cis-[6-(1-hydroxypropyl)-2-piperidyl]acetic acid. The same conclusion holds for palustrin and dihydropalustrin. Therefore, palustrin is threo-cis-17-(1-hydroxy-propyl)-1,5,10-triazabicyclo[11.4.0]heptadec-15-en-11-one.     

Synthese und Charakterisierung der 8 isomeren,im Ring B mono- bzw. dihydroxylierten Royleanone

Synthesis and Characterization of the 8 Stereoisomeric Royleanones with One or Two Hydroxy Groups in Ring B The partial syntheses of 6α, 7α-dihydroxyroyleanone ( 6a ), 6α, 7β-dihydroxyroyleanone ( 7a ) and 6β, 7β-dihydroxyroyleanone ( 9a ) are described. Thus, all in ring B mono- and dihydroxylated royleanones are now known (see [2–11]), being fully characterized by extensive spectroscopic, chiroptic and chromatographic (HPLC.) methods. An opening of the epoxyroyleanone 11a yields cis- and trans-diols together with their corresponding mono- and di-O-acetyl derivatives. We postulate a reversible addition of the acetate ion at C(8) of the quinone system, followed by a neighbouring group participation of this O-acetyl group.     

Potentiometric titration of cyanide and chloride, using the silver specific-ion electrode as an indicator

Conditions are given for consecutive potentiometric titration of cyanide and chloride in mmole amounts, a silver-specific electrode being used as indicator electrode.     

Solid-supported synthesis of putative peptide beta-turn mimetics via Ugi reaction for diketopiperazine formation

The scope and limitations of the solid-supported synthesis of a bicyclic diketopiperazine, an internal, putative peptide beta-turn mimetic, are presented. The 4CC multicomponent Ugi reaction of alpha-N-Boc-diaminopropionic acid resin ester (an amine input), optically active alpha-bromoacid, aldehyde, and isocyanide is the key step in the proposed synthetic protocol. Application of cyclitive cleavage as the final step led to desired products in high purity.     

Fredericone,neue hochfunktionalisierte Abietanoide aus Blattdrüsen von Coleus fredericii G. TAYL

Fredericon A, B, C, and D, Novel and Highly Functionalized Abietanoids from Leaf-Glands of Coleus fredericii From the leaf-glands of the title plant (fam. Labiatae) two novel, genuie spirocycloopropyl-coleons have been isolated and structurally characterized. Fredericon A (1) bears the unusal 1,1,2-tricarbonylcyclopropane substructure that renders the molecule very suseptible to nucleophile-promoted rearrangements. Biogenetically intriguing is the presence of a 3-acetoxypropyl side-chain in fredericon B ( 3 ). Its formation from the well known isopropyl group is explained by transformation of the latter into a spirocyclopropane, followed by a reductive opening of the cyclopropane and reducation of the aldehyde, MeOH addition to 1 , yields fredericon C ( 5 ), a derivative of 1H-phenanthro[3,2-b]pyran-7,12(2H,8H)-dione by two consecutive introlecular nucleophilic openings of the cyclopropane ring and the derived methoxy-oxirane. Similar methanolysis of a crude fraction of 1 , produced, in addition to 5 , the fredericon D, a novel derivative of 3H-phenanthro[3,2-b]pyran-2-(4H)-one( 6 ).     

Absolute Konfiguration von α-Doradexanthin und von Fritschiellaxanthin,einem neuen Carotinoid aus Fritschiella tuberosa IYENG

Absolute Configuration of α-Doradexanthin and of Fritschiellaxanthin, a New Carotenoid from Fritschiella tuberosa IYENG . Fritschiellaxanthin, a new oxocarotenoid produced by the green alga Fritschiella tuberosa, in a nitrogen-deficient medium is now shown to be (3 S, 3′ R, 6′ R)-3, 3′-dihydroxy-β, ?-caroten-4-one ( 4b ). It is not identical with α-Doradexanthin ( 5b ) previously found in goldfish (Carassius auratus) and to which we assign the (3 S, 3′ S, 6′ R)-chirality. Consequently, fritschiellaxanthin and α-Doradexanthin are C(3′)-epimers of lutein-4-on. Furthermore, the so-called ′lutein′ from goldfish has now been found to be identical with 3′-epilutein (3) . Therefore, fritschiellaxanthin is probably biogenetically derived from lutein (2) , whereas α-Doradexanthin is formed from 3′-epilutein (3) with 3, O-didehydrolutein (=(3R, 6′R)-3-hydroxy-β, ?-caroten-3′-one 10) as a precursor. For comparison, optically active 10 and 3 have been prepared from lutein (2) and are fully characterised.     

UPS study of cyanogen adsorbed on Pt(100)

Ultraviolet photoelectron spectra for adsorbed cyanogen on Pt(100) are presented and discussed in terms of possible models for the different adsorption states detected by other surface techniques. Taking the gas phase spectra of C₂N₂ and HCN as guidance interpretation of the various cyanogen induced features is attempted as follows: A prominent peak 6 eV below the Fermi level is ascribed to the overlapping π and nitrogen lone-pair orbitals, whereas a weak, broad feature around 16 eV is assigned to CC π bonds present in the absorbate layer. A feature within the Pt d-band region at 3 eV is tentatively associated with the “back-bonding” from filled metal d-band states into empty 2π^* states of the absorbate.     

Azokupplungen an 3,4-Dimethoxyfuran

Diazo coupling of 3,4-dimethoxyfuran with aryl diazonium ions 3,4-Dimethoxyfuran ( 1 ) easily reacts with aryl diazonium chloride in aqueous pyridine in an expected 1, 4-addition reaction. From the isolable primary addition product pyridine is displaced by alcohols, phenols or thiols to yield 4-alkoxy- or 4-phenoxy- or 4-thiophenoxy-derivatives of 2,3-dimethoxy-2-buten-4-olide ( 3 ). Attempts to convert them into azo compounds by a base catalysed 1, 6-elimination reaction failed. Oxidation of 3a and 3c with DDQ results in the formation of the mono p-nitrophenylhydrazone of 3, 4-dimethoxymaleic acid anhydride. On the other hand, the thiophenoxy compound 3g is smoothly converted by MnO₂ into the authentic furan-2-azobenzene derivative 5 .     

Synthesis of pyrido[3,4-d] benzazepines

The synthesis of some derivatives of the novel heterocyclic ring system pyrido[3,4-d][1]benzazepine is reported. Thus, pyrido[3,4-d][1]benzazepin-7-one 6 was prepared by cyclisation of the Michael adduct 5 with ammonium ferric sulfate. Reaction of 6 with phosphorus pentasulfide gave the thiolactam 7 , which after methylation and subsequent reaction with amines furnished the amidines 10 .