Showing papers in "Helvetica Chimica Acta in 1988"

Semicorrin metal complexes as enantioselective catalysts. Part 2. Enantioselective cyclopropane formation from olefins with diazo compounds catalyzed by chiral (semicorrinato)copper complexes

Abstract: Copper complexes of chiral, C2-symmetric semicorrin ligands were found to be efficient catalysts for the cyclopropane formation from olefins with diazo compounds. In the presence of 1 mode-% of catalyst, alkyl diazoacetates reacted smoothly with terminal olefins such as styrene, butadiene, and 1-heptene to give the corresponding optically active cyclopropanecarboxylic-acid derivatives (Table 1 Scheme 2). With one of the catalysts, enantioselectivities up to 97% ee were obtained (Table 2). Usually, the reactions were carried out using bis(semicorrinato)copper(II) complexes as precatalysts. In order to produce active catalysts, these complexes had to be activated first by heating in the presence of diazoacetate or by treatment with phenylhydrazine. Experiments with (semicorrinato)copper(I) complexes, prepared in situ from copper(I) tert-butoxide (Scheme 4), suggest that the actual catalyst is a [mono(semicorrinato)]copper(I).

Synthesis of D-Erythro- and D-Threo-Sphingosine Derivatives From L-Serine

Abstract: The protected serine aldehyde 10 was converted to the crystalline N-Boc-protected sphingosines 6–9 by a three-step reaction sequence. Compound 10 was transformed with high diastereoselectivity (95%) either to the erythro- or threo-alkynols, 17 and 18, respectively. The erythro-isomer 17 is formed by the addition to 10 of lithium pentadecyne 16 in THF/HMPT at −78°, whereas the corresponding threo-isomer 18 is produced in the presence of ZnBr2 in Et2O. Deprotection of the acetal moiety afforded 1,3-diols 19 and 20. These diols were selectively reduced with Red-Al to the (E)-sphingosines 6 and 8, or the (Z)-isomers 7 and 9 by partial hydrogenation over Lindlar's catalyst. Cleavage of the N-Boc group and further transformation to ceramides were readily achieved as demonstarted by the conversion of 6 to N-octadecanoyl-D-erythro-sphingosine 5.

Axially dissymmetric bis(triaryl)phosphines in the biphenyl series: synthesis of (6,6'-dimethylbiphenyl-2,2'-diyl)bis(diphenylphosphine) (BIPHEMP) and analogues, and their use in Rh(I)-catalyzed asymmetric isomerizations of N,N-diethylnerylamine

Abstract: The axially dissymmetric diphosphines (−)-(R)- and (+)-(S)-(6-6′-dimethylbiphenyl-2,2′-diyl)bis(diphenyl-phosphine) ((−)-(R)-10 and (+)-(S)-10; ‘BIPHEMP’) have been synthesized, starting from (R)- and (S)-6,6′-dimethylbiphenyl-2,2′-diamine ((R)- and(S)-16), respectively, via Sandmeyer reaction, liathiation, and phosphinylation. Moreover, racemic 4,4′- dimethyl- and 4,4′-bis(dimethylamino)-substituted analogues 11 and 12 respectively, and the 6,6′-bridged analogues 1,11-bis(diphenylphosphino)-5,7-dihydrodibenz[c,e]oxepin (13) were synthesized and resolved into optically pure (R)- and(S)-enantiomers via complexation with di-μ-chlorob is {(R)-2-[1-(dimethylamino)ethyl]pheny-CN}dipalladium(II) ((R)-18). The molecular structures of the diphosphines (S)-10 and (R)-13 and of two derived cationic Rh(I) complexes,[Rh((S)- 10)(nbd)]BF4 and [Rh((R)- 13)(nbd)]BF4 were determined by x-ray analyses. Absolute configurations were established for (+)-(S)- 10 by X-ray analyses of both the free diphosphine and of the derived Rh(I) complex, and for (−)-(R)- 13 by X-ray analysis of the derived Rh(I) complex. Configurational assignments for the substituted BIPHEMP analogues 1112 were achieved by means of 1H-NMR comparisons. The BIPHEMP ligand 10 and analogues 11, 12 and 13 are the first examples of optically active bis(triaylphosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asymmetry-inducing ligands in Rh(I)-catalyzed isomerizations of N,N-diethylnerylamine affording citronellat enamine of 98-99% ee.

Diastereoselektive Alkylierung von 3‐Aminobutansäure in der 2‐Stellung

Abstract: Diastereoselective Alkylation 3-Aminobutanoic Acid in the 2-Position The enantiomerically pure 3-aminobutanoic acids (R)- and (S)-6 are readily available by preparative HPLC separation of the two diastereoisomers 5 obtained from addition of (S)-phenethylamine to methyl crotonate and subsequent hydrogenolysis (Scheme 2). (S)-Methyl 3-(benzoylamino) butanoate ((S)-3) is also available by enzymatic kinetic resolution with pig-liver esterase. The N-benzyl- and N- benzyloxycarbonyl derivatives rac3,8, and 9 of 3-aminobutanoates are doubly deprotonated with LDA and alkylated or aminated in high selectivity (17 examples, relative topicity like; see Tables 1 and 2). The configuration of three of the products is assigned (Schemes 4–6), and in four cases, the free α-substituted β-amino acid is prepared by acidic hydrolysis (see Table 3). It is shown that the doubly lithiated β-amino-acid derivative is solubilized, and its reactivity may be strongly influenced by the presence of 3 equiv. of LiCl.

Solid‐Phase Synthesis of Oligodeoxynucleotides containing phosphoramidate internucleotide linkages and their specific chemical cleavage

Abstract: Oligonuclecotides bearing phosphoramidate internucleotide linkages can be prepared chemically by standard solid-phase DNA synthesis. Thus, phosphoramidate internucleotide bonds can be placed at will into specific positions within a given DNA fragment. The backbone-modified DNA fragments prepared in this way are susceptible to a specific chemical cleavage.

Absorption Spectra and Luminescence Properties of Isomeric Platinum (II) and Palladium (II) Complexes containing 1,1′-biphenyldiyl, 2-phenylpyridine, and 2,2′-bijpyridine as ligands

Abstract: The absorption spectra, luminescence spectra, and luminescence lifetimes of the isomeric [M(bph)(bpy)] and [M(phpy)2] complexes M = Pt(II) or Pd(II), bph2− = 1,1′-biphenyl-2,2′-diyl dianion, phpy− = 2-phenylpyridine-2′-yl anion, and bpy = 2,2′-bipyridine have been investigated and compared with those of [M(bpy)2]2+ complexes and of the free protonated ligands H2bph, Hbpy+, and Hphpy. In the absorption spectra, the region below 320 mm is dominated by ligand-centered (LC) transitions, whereas metal-to-ligand charge transfer (MLCT) transitions are responsible for the bands present in the near UV/VIS region. The MLCT bands move to higher energies on replacing Pt with Pd and in going from [M(bph)(bpy)] to the [M(phpy)2] isomer. For the mixed-ligand complexes, evidence for both M bph2− (at higher energies) and M bpy bands is found. The structured luminescence observed at 77 K shows lifetimes of 4.0 and 1.1 μs for [Pt(phpy)2] and [Pt(bph)(bpy)], respectively, and 480 and 250 μs for the analogous Pd complexes. On the basis of the energy and lifetime data, the luminescence of the Pt(II) complexes is assigned to the lowest triplet MLCT excited state, whereas for the Pd complexes the luminescent state is thought to result from a mixture of MLCT and LC triplet levels.

Semicorrin Metal Complexes as Enantioselective Catalysts. Part 1. Synthesis of chiral semicorrin ligands and general concepts

Abstract: An efficient synthesis of chiral semicorrin ligands is described (see 6–9, Schemes 2 and 3). Both enantiomers are readily obtained in enantiomerically pure form starting either from D-or L-pyroglutamic acid (1). Semicorrins of this type possess several features that make them attractive ligands for enantioselective control of metal-catalyzed reactions. Their structure is characterized by C2 symmetry, a conformationally rigid ligand system, and two stereogenic centers adjacent to the coordination sphere. In a metal complex, the two substituents at the stereogenic centers shield the metal atom from two opposite directions and, therefore, are expected to have a pronounced effect on the stereochemical course of a reaction occurring in the coordination sphere. The structure of these two substituents can be easily modified in a variety of ways. A series of (semicorrinato)copper(II) complexes (see 10–14, Scheme 4) has been prepared, and in one case (14), the three-dimensional structure has been determined by X-ray analysis (Fig. 1).

Synthesis and Characterisation of the Sodium and Lithium Cryptates of Macrobicyclic Ligands incorporating pyridine, bipyridine, and biisoquinoline units

Abstract: Sythetic procedures have been deweloped for the preparation of sodium and lithium cryptates of the macrabicyclic ligands 1–11 containing pyridine, bipyridine, and biisoquinoline groups. They involve stepwise construction of the bicyclic system as will as direct macrobicyclisation procedures (Scheme 1) and give access to both symmetrical and dissymmetrical structures. Marked cation template effects have been found that facilitate the cyclisation processes. The ligands 1–11 were isolated as their cryptates with Na+ or Li+ cations.

The Construction of New Proteins. Part III. Artificial folding units by assembly of amphiphilic secondary structures on a template

Abstract: A new general strategy for the construction of artificial proteins with predetermined tertiary structure is presented. Amphiphilic α-helix and β-sheet-forming oligopeptides are assembled on a multifunctional ttemplate molecule which directs the peptide blocks to adopt characteristic folding topologies. The design, synthesis, and conformational properties of these template-assembled synthetic proteins (TASP) are exemplified for βαβ-, α-helix-bundle- and β-barrel-like tertiary structures using specially designed oligopeptides as template molecules. In contrast to linear polypeptide chains of comparable molecular weights, these conceptually novel marcromolecules are readily accessible to chemical synthesis and exhibit excellent solubility in a number of solvents. Experimental evidence is provided for a template-induced intramolecular folding to secondary and tertiary structures in aqueous solutions. This approach opens new prospects for the chemical construction of biomacromolecules with tailormade structural and functional properties.

Bathophenanthroline-ruthenium(II) complexes as non-radioactive labels for oligonucleotides which can be measured by time-resolved fluorescence techniques

Abstract: The specific attachment of bathophenanthroline-ruthenium(II) complexes as non-radioactive label molecules to synthetically 5′-NH2-modified oligonucleotides is described. After excitation by light pulses, the fluorescence of these labels can be measured by a time-resolved mode woth high sensitivity. No quenching takes place due to coupling of the Ru complexes to the DNA. Ru-complex-labelled oligonucleotides still hybridize specifically to complementary DNA sequences, and no quenching is observed in the course of the hybridization process.

A Synthesis of 1D- and 1L-myo-Inositol 1,3,4,5,-Tetraphosphate

Abstract: A synthesis of 1D- and 1L-myo-inositol 1,3,4,5,-tetraphosphate (1a and 1b resp.) is described. The dibenzylated myo-inositola 9a and 9b, which, by phosphorylation, gave 1a and 1b, respectively, were prepared via two routes. On the one hand, the racemate 3a/3b, obtained from myo-inositol, was resolved by its transformation into the diastereoisomeric carbamates 5a and 5b. Benzylation and deprotecton of 5a and 5b gave the enantiomers 9a and 9b, respectively. On the other hand, treatment of the diester 18 with pig liver esterase gave the ester 21a with high enantiomeric excess. Benzylation and deprotection of 21a yielded 9b. The dibenzyl derivative 9a was obtained using the same enzymatic hydrolysis followed by a protection-deprotection sequence.

Silicon‐Directed Nazarov Cyclizations. Part V. Substituent and heteroatom effects on the reaction

Abstract: The ability to incorporate alkyl, alkenyl, aryl, and heteroatomic groups into substrates for the silicon-directed Nazarov cyclization and their subsequent reactions has been investigated. In general, most of the groups are compatible with the conditions for the cyclization and do not interfere even when directly attached to the divinyl ketone. The influence of substituents on the rate of the cyclization has been addressed and is consistent with a simple mechanistic picture. O- and N-Containing functions are tolerated except when attached to the α-vinyl C-atom of the divinyl ketone. The diastereoface-directing effect of a fused cyclobutane is discussed.

Free-energy dependence of the ion yield of photo-induced electron-transfer reactions in solution

Abstract: A study of photo-induced electron-transfer reactions in MeCN with 9,10-dicyanoanthracene as acceptor and 21 electron donors with transient photoconductivity measurements is reported. The free-ion yield and the rate constant of back electron transfer are determined. For exergonic reactions, the ‘Marcus-inverted’ region is observed. The fit with the theory is best, when a nearly solvent-independent Coulomb term is used in the calculation of the energy balance.

Anion-receptor molecules: macrocyclic and macrobicyclic effects on anion binding by polyammonium receptor molecules

Abstract: The stability constants for anion binding by the acyclic hexaamine 1, its macrocyclic analogue 2, and the bicyclic compound 3 in their protonated forms are reported. Compound 3 forms stable and selective complexes with halide ions, the stability sequence being I− > Br− > Cl−. Compound 2 forms more stable complexes with sulfate, oxalate, and malonate dianions than its acyclic analogue 1 and shows a better selectivity pattern. Compound 3 forms stronger complexes with oxalate2− than 2 and shows a remarkably high binding selectivity between oxalate2− and malonate2−. The comparison of the ability of 1–3 to complex anions demonstrates the macrocyclic and macrobicyclic effects on anion binding stability and selectivity.

Note on the Preparation of 1,2‐Diketones from Acetylenes

Abstract: A mild method for the oxidation of acetylenes to 1,2-diketones using NaIO4/RuO2 is described. An investigation on the compatibility of various functional groups with this oxidizing agent is reported.

Anion-receptor molecules: Synthesis of a chiral and functionalized binding subunit, a bicyclic guanidinium group derived from L- or D- asparagine

Abstract: The optically active (4S,8S)-4, 8-bis(hydroxymethyl)-1,5,7-triazabicyclo[4.4.0]dec-5-ene ((S,S)-1) has been synthesized in nine steps from L-asparagine with a total yield of 5.1%. Similarly, the enantiomer (R,R)-1 has been prepared from D-asparagine. (S,S)- and (S,S)-1 are representative examples of rigid and functionalized bicyclic guanidine systems and constitute useful intermediates in the construction of chiral selective anion-receptor molecules.

Isolation from the Mediterranean Stolonifern Coral Sarcodictyon roseum of Sarcodictyin C, D, E, and F, novel diterpenodic alcohols esterified by (E)‐ or (Z)‐N(1)‐methylurocanic acid. Failure of the carbon‐skeleton type as a classification criterion

Abstract: It is shown here that the stoloniferan coral Sarcodictyon roseum of east Pyrenean waters contains four novel diterpenoids, sarcodictyin C ((−)-3), D ((−)-4), E ((+)-5), F ((+)-6), which are related to sarcodictyin A ( = (−)-(4R,4aR,7R,10S,11S,12aR,1Z,5E,8Z-7,10-epoxy-3,4,4a,7,10,11,12,12a-octahydro-7-hydroxy-6-(methyoxycarbonyl)-1,10-dimethyl-4-(1-methylethyl)-benzocyclodecen-11-yl (E)-N1-methylyrocanate; ((−)−1), previously isolated from the same coral. Sarcodictyin C ((−)-3) and D ((−)-4) and the 3α-hydroxy and 3α-acetoxy derivatives of (−)-1), sarcodictyin E ((+)-5) is the (Z)-urocanate isomer of (−)-3), and sarcodictyin F ((+)-6) is the 1α-hydroxy-2-ene isomer of (−)-3. In all cases, the nine-membered ring is locked, and the molecule stabilized, by the urocanic appendage; when this is removed in MeOH/KOH, the C(11)–O− function is free to attack at C(5), and retro-condensations then lead to the ring-contracted butenolides 11 (from (−)-3) or 10 (from(−)-1) with extrusion of the hydroxyfuran nucleus (Scheme 3). Under the same conditions, with (−)-3, the C(3)-O− group competitively attacks at C(5), the hydroxyfuran nucleus is expelled, and aldehyde 14 is formed. Peculiarly, in the reaction of (−)-3 with MeOD/KOD, the ring-contracted butenolide 17 contains D at the 4′-ax position. The sarcodictyins are unique in these chemical properties, not shared by the cladiellanes which have the same C-skeleton.

The Structure of the Polycyclic Nonadecapeptide Ro 09-0198†

Abstract: The conventional determination of the amino-acid sequence of the peptide antibiotic Ro 09-0198 was prevented by four cyclizations via side chains. The joint application of NMR spectroscopy at highest field and automated Edman degradation yielded a complete determination of the connectivity pattern. The three-dimensional structure derived from NOE data exhibits an interesting separation of amino acids with hydrophilic and hydrophobic side chains.

A new synthesis of N‐acetylneuraminic acid

Abstract: A new synthesis of N-acetylneuraminic acid (Neu5Ac; 28) via aldehyde 10 is described. The aldehyde 10 was obtained from N, acetyl-D-glucosamine (11; 5 steps, overall yield ca. 6%) or from D-glucono-1,5-lactone (17; 6 steps, overll yield ca 57%). Thus, on the one hand, N-acetyl-D-mannosamine (12), obtained from 11, was transformed into the known dithioacetal 14 and hence into the (ethylthio)dihydrooxazole 16, which was cleaved under weakly acidic conditions to the aldehyde 10. On the other hand, the known ester 18, obtained from 17, was sulfonylated and further transformed via the azide 20 into the N-acetyl-D-mannonate 22. Reduction of 22 to 23 and oxidation of 23 with ‘periodinane’ again gave 10. The aldehyde 10 was treated with the organozinc reagent 8 obtained from tert-butyl 2-(bromomethyl)acrylate (2) to yield predominantly 24, which was transformed (two steps) into the 2-methylidene-D-glycero-nononic acid 27 and hence into Neu5Ac (28).

Novel Aplysinopsin‐Type Alkaloids from Scleractinian Corals of the Family Dendrophylliidae of the Mediterranean and the Philippines. Configurational‐assignment criteria, stereospecific synthesis, and photoisomerization

Abstract: From the scleractinian coral Tubastraea sp. (Dendrophylliidae) collected at Palawan, Philippines, 3′-deimino-3′-oxoaplysinopsin (4) and 6-bromo-3′-deimino-3′-oxoaplysinopsin (6) are now isolated as 5:2 mixtures of (E/Z) stereoisomers. The 3′-deimino-2′,4′-bis(demethyl)-3′-oxoaplysinopsin (7) and 6-bromo-3′-demino-2′,4-bis(demethyl)-3′-oxoaplysinopsin (5) are isolated as 2:3 and 1:1 (E/Z) mixtures, respectively, from another dendrophylliid, Leptopsammia pruvoti, collected near Marseille, Mediterranean coast of France. Larger amounts of these and related compounds, needed for a full structural determination, are obtained by synthesis. Thus, condensations of indol-3-carboxaldehyde (9) or of its 6-bromo derivative 14 with hydantoin (15), 3-methylhydantoin (11), or 1,3dimethylhydantoin (10) give the prevalent natural aplysinopsins with high stereospecificity. The minor stereoisomers (Z)-4, (Z)-6, (E)-7, and (E)-5 are obtained by (E/Z) photoisomerization under UV light of the condensation mixtures. The configuration is assigned from larger HC(8)/C(5′) 1H, 13C couplings in the (E) than in the (Z) isomer, and, in the case of 4 and 6, from NOE enhancement at MeN(2′) on irradiation at HC(8). The stereospecificity of the condensations is attributed to steric inhibition to planarity in the rate-limiting transition states, due to N(2′)/HC(2) repulsion with (Z)-4 and (Z)-6, or to C(5′)O/HC(2) repulsion with (E)–7 or (E)-5. As the aplysinopsins undergo (E/Z ) phostoisomerization also under the daylight conditions of the laboratory, their isomeric composition in nature can not be presently assessed.

Enantiomerically Pure 7-Oxabicyclo[2.2.1]Hept-5-En-2-Yl Derivatives as Synthetic Intermediates .3. Total Synthesis of D-Ribose and L-Ribose Derivatives

Abstract: Note: Univ lausanne,ist chim organ,2 rue barre,ch-1005 lausanne,switzerland. Reference LGSA-ARTICLE-1988-003doi:10.1002/hlca.19880710316 Record created on 2005-11-09, modified on 2017-05-12

Spectroscopic and Electrochemical Behavior of Cyclometalated Pd(II) Complexes

Abstract: The absorption and emission spectra, emission lifetimes, luminescence quantum yields, and electrochemical behavior of the complexes Pd(Phpy)2, Pd(Thpy)2, and Pd(bhq)2 (Phpy−, Thpy−, and bhq−, and bhq− are the deprotonated forms of 2-phenylpyridine, 2-(2-thienyl)pyridine, and benzo[h] quinoline, respectively) have been studied, and the results obtained have been compared with those available for Pt(II) and Pt(IV) complexes containing the same ligands. The intense ligand-centered absorption bands below 340 nm are strongly perturbed by matalation, and the absorption features in the 340–450-nm region are likely to include contributions from formally metal-to-ligand charge-transfer transitions. The structured luminescence spectra observed at 77 K (lifetimes are 0.48, 0.28 and 2.6 ms for Pd(Phpy)2, Pd(Thpy)2, and Pd(bhq)2, respectively) have been assigned to transitions having mainly ligand-centered character, with an increasing metal-to-ligand charge-transfer contribution in going from Pd(bhq)2 to Pd(Phpy)2 and to Pd(Thpy)2. The complexes Pd(phpy)2 and Pd(thpy)2 show two reversible one-electron reduction waves, whereas reduction of Pd(bhq)2 is irreversible, as is the oxidation of the three complexes.

Complexes with a Pincers. 2,6‐Diphenylpyridine as Twofold‐Deprotonated (C ∧ N ∧ C) terdentate ligand in C,C‐trans‐, and as mono‐deprotonated (C ∧ N) chelate ligand in chiral C,C‐cis‐complexes of platinum(II) and palladium(II). Preliminary communication

Abstract: A2,6-Diphenylpyridine forms, as twofold-deprotonated, terdentate ligand, complexes with Pt(II) and Pd(II), having two adjacent five-membered metallocycles. As mono-deprotonated, bidentate ligand, it forms cis-bis-complexes having a chirality axis. Pt(II) complexes undergo thermal and photochemical oxidative addition reactions, yielding stable Pt(IV) compounds. Pd(II) complexes yield substitued 2,6-diphenylpyridine in photochemical reactions.

8-Aza-7-deazaadenine N8- and N8-(β-D-2′-Deoxyribofuranosides): Building blocks for automated DNA synthesis and properties of oligodeoxyribonucleotides

Abstract: Oligonucleotides with alternating 8-aza-7-deaza-2′-deoxyadenosine (= c7z8Ad2) and dT residues (see 11, 14 and 16) or 4-aminopyrazolo [3,4-d] pyrimidine N2-(β-D-2′-deoxyribofuranoside) (= c7z8A′d1); (3) and dT residues (see 12) have been prepared by solid-phase synthesis using P(III) chemistry, Additionally, palindromic oligomers derived from d(C-T-G-G-A-T-C-C-A-G) but containing 2 or 3 instead of dA (see 18–22) have been synthesized. Benzoylation of 2 or 3, followed by 4,4′-dimethoxytritylation and subsequent phosphitylation yielded the methyl or the cyanoethyl phosphoramidites 8a,b and 9. They were employed in automated. DNA synthesis. Alternating oligomers containing 2 or 3 showed increase dTm values compared to those with dA, in particular 12 with an unusual N2-glycosylic bond. The palindromic oligomers 18-22 containing 2 or 3 instead of dA outside of the enzymic recognition side reduced the hydrolysis rate, replacement within d(G-A-T-C) abolished phosphodiester hydrolysis.

Anwendungsbreite der reduktiven Kupplung aromatischer Aldimin‐Derivate mit niedervalenten Titan‐Reagenzien zu 1,2‐Diarylethylendiaminen

Abstract: Scope and Limitations of the Reductive Coupling of Aromatic Aldimine Derivatives with Formation of 1,2-Diarylethylenediamine Units, Using Low-Valent Titanium Reagents Besides the adducts from lithium amides to aromatic aldehydes, iminium salts, animals, and N-silylimines of aromatic aldehydes are coupled by the black suspension obtained from TiCL4 and Mg turnings in tetrahydrofuran (THF). The 1,2-diarylethylenediamines with tertiary and primary amino groups thus obtained are formed with no or only moderate diastereoselectivity (products 4a–d(Scheme 2) and 5–e(Scheme 3), respectively); the amine component may contain a strained ring or additional heteroatoms as in azetidin, bis(2-methoxyethyl)amine, piperazine, morpholine, and thiomorpholine (products 6a–e; Table 1). By an in-situ procedure, ethylenediamines exclusively trans-diaryl-substituted piperazine and perhydro-1,4-diazepine derivatives (products 7a–f; Table 2). Enantiomerically pure monocyclic trans,cis-5-alkyl-2,-3-diaryl-piperazines and diazabicyclo[4.3.0]nonanes and -[4.4.0]decanes are obtained by employing suitable diamines prepared from the amino acids (S)-alanine, (S)-phenylalanine, (S)-proline and from (S,S)- or (R,R)-cyclohexane-1,2-diamine, respectively (products 11a–i, 7e; Table 4). The configuration of all products are derived from the high-field NMR spectra, some of which are discussed in detail (Figs. 1 and 2, Tables 3 and 5); all new compounds are fully characterized by their physical data. Depending upon the structure of the components employed, the yields of purified products range from as low as 7% to essentially quantitative.

Lavandulifolioside a new phenylpropanoid glycoside from stachys lavandulifolia

Abstract: A new phenlypropanoid glycoside has been isolated from the methanolic extract of the aerial parts of Stachys lavandulifolia (Lamiaceae), lavandulifolioside (1). On the basis of chemical and spectral data the structure of the new compound 1 has been elucidated as β-(3,4-dihydroxyphenyl)ethyl O-α-L-arabinopyranosyl-(12)-α-L-rhamnopyranosyl-(13)-4-O-caffeoyl-β-D-glucopyranoside.

Stereoselective synthesis of pyrrolo[2,3‐d]pyrimidine α‐ and β‐D‐ribonucleosides from anomerically pure D‐ribofuranosyl chlorides: Solid‐Liquid Phase‐Transfer Glycosylation and 15N‐NMR Spectra

Abstract: Solid-liquid phase-transfer glycosylation (KOH, tris[2-(2-methoxyethoxy)ethye]amine ( = TDA-1), MeCN) of pyrrolo[2,3-d]pyrimidines such as 3a and 3b with an equimolar amount of 5-O-[(1,1 -dimethylethyl)dimethylsilyl]-2,3-O-(1-methylethylidene)-α-D-ribofuranosyl chloride (1) [6] gave the protected β-D-nucleosides 4a and 4b, respectively, stereoselectively (Scheme). The β-D-anomer 2 [6] yielded the corresponding α-D-nucleosides 5a and 5b with traces of the β-D-compounds. The 6-substituted 7-deazapurine nucleosides 6a, 7a, and 8 were converted into tubercidin (10) or its α-D-anomer (11). Spin-lattice relaxation measurements of anomeric ribonucleosides revealed that T1 values of HC(8) in the α-D-series are significantly increased compared to HC(8) in the β-D-series while the opposite is true for T1 of HC(1′). 15N-NMR data of 6-substituted 7-deazapurine D-ribofuranosides were assigned and compared with those of 2′-deoxy compounds. Furthermore, it was shown that 7-deaza-2′deoxyadenosine ( = 2′-deoxytubercidin; 12) is protonated at N(1), whereas the protonation site of 7-deaza-2′-deoxyguanosine (20) is N(3).

Ruthenium(II) complexes with three different diimine ligands

Abstract: The synthesis of tri-heteroleptic complex of Ru(II) with diimine ligands is describe. Ten compounds [Ru(R2bpy) (biq) (L)][PF6]2 (R = H, CH3); L = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), 2,2′-bipyrimidine (bpm), 2,2′-biisoquinoline (biiq), 1,10-phenanthroline (phen), dipyrido[3,2-c:2′,3′-e]pyridazine (taphen), 2,2′-biquinoline (biq), 6,7-dihydrodipyrido[2,3-b:3,2-j][1,10]-phenanthroline (dinapy), 2-(2[pyridyl)quinoline (pq), 1-(2-pyrimidyl)pyrazole] (pzpm), 2,2′-biimidazole (H2biim) are characterized by elemental analysis, electronic and 1H-NMR spectroscopy. The relative photosustitution rates of biq in MeCN are given at three temperatures.

Synthesis of selectively trifluoromethylated pyridine derivaties as potential antihypertensives

Abstract: A general synthesis of selectively 6-(trifluoromethyl)-substitued 2(1H)-pyridinones is described. Further transformation of one of these compounds leads to the new CF3-containing potassium-channel openers 2a and 2b.

Herstellung enantiomerenreiner, α‐alkylierter Lysin‐, Ornithin‐ und Tryptophan‐Derivate

Abstract: Synthesis of Enantiomerically Pure, α-Alkylated Lysine, Ornithine, and Tryptophan Derivatives The imidazolidinones 9 and 10 as well as the oxazolidinone 18a were prepared in several steps by known methods from lysine and ornithine with an overall yield of ca. 20%. After double deprotonation with LDA, the corresponding dianionic derivatives could be diastereoselectively alkylated with electrophiles (MeI, C6H5CH2Br, C6H5CHO, CH3CHO). Acid hydrolysis led to the two enantiomeric 2-methyl- and 2-benzyllysines and to the enzyme inhibitor (S)-2-methylornithine. Several α-alkylated tryptophan derivatives were obtained through alkylation of the heterocycles derived from various amino acids with 1-(tert-butyloxycarbonyl)-3-(bromomethyl)indole (26). Alkaline hydrolysis of the five-membered auxiliary ring of 30b followed by treatment with HCl afforded (S)-2-methyltryptophan (31).