Amidine als Zwischenprodukte bei Umamidierungsreaktionen. 9. Mitteilung über Umamidierungsreaktionen

Amidines as Intermediates in Transamidation Reactions By loss of water in the presence of p-toluenesulfonic acid/xylole N-aminoalkyllactames form bicyclic amidines. The corresponding N-alkylaminoalkyl-lactames' react to bicyclic amidinium salts or to transamidated products, ring-enlarged by the N-alkylamino residue, respectively (s. Scheme 1). The bicyclic amidines and amidinium salts are partially hydrolyzed by KOH/H₂O to lactames (s. Scheme 2). Which of the two possible isomeric lactames are formed is discussed.     

Unconventional large-N limit of the Gaussian effective potential and the phase transition in λφ 4 theory

In the conventional large-N limit the coupling constant is required to scale as 1/N. While the Gaussian effective potential (GEP) is known to contain the exact result in this limit, it shows a phase transition only when 1/N (in units of the renormalized mass in the symmetric vacuum). Here we determine the asymptotic behaviour, asN, of and other quantities at the phase transition of the GEP. We find _crit to be finite in 0+1 dimensions; of order 1/lnN in 1+1 dimensions; 1/N ^1/3 in 2+1 dimensions; and in 3+1 dimensions. The GEP's first-order phase transition is shown to become asymptotically second-order in 1+1 dimensions and below. We also discuss non-integer dimensions and the approach to the non-trivial autonomous theory in 3+1 dimensions.     

Synthese von selektiv N- funktionalisierten Polyamin-Derivaten

Synthesis of Selectively N-Functionalized Polyamine Derivatives A threefold differently protected derivative 8 of the triamine spermidine ( 2 ) has been prepared in three steps starting from propane-1,3-diamine ( 1 ). The protected spermidine derivative 8 was converted to its spermine analogue 12 , a useful polyamine intermediate. In a convergent way, the fourfold differently protected derivative 18 of the tetraamine spermine ( 3 ) has been obtained by coupling the two different and separately prepared propane-1,3-diamine units 15 and 17 . Spermidine derivative 19 and spermine derivative 20 , both selectively protected at both primary amino groups, have been Prepared from the free polyamines 2 and 3 , respectively, in a direct approach.     

Aristoserratin,ein neues Indolalkaloid aus Aristotelia serrata W.R.B. OLIVER und A. peduncularis (LABILL.) HOOK. F. 178. Mitteilung über organische Naturstoffe

Aristoserratine, a New Indole Alkaloid from Aristotelia serrata W.R.B. OLIVER and from A. peduncularis (LABILL .) HOOK . F. The new indole alkaloid aristoserratine (2) has been isolated from Aristotelia. Its structure and absolute configuration were elucidated on the basis of spectroscopic data.     

Synthesis of Oncinotin-11-one,a Macrocyclic Polyamine Alkaloid from Oncinotis tenuiloba

This paper presents a short synthesis of oncinotin-11-one ( 11 ), a minor alkaloid of Oncinotis tenuiloba (Apocynaceae). Based on a disconnection approach, the spermidine portion of the key intermediate 6 was constructed consecutively by simple N-alkylations starting from ethyl piperidine-2-carboxylate ( 1 ). Treatment of 6 with in situ lithiated 2-[(10-bromodecyl)oxy]tetrahydropyran resulted in the formation of the keto moiety under simultanous deprotection of the lactam N-atom to give the amino ketone 7 in 71% yield. Cleavage of the tetrahydro-2H-pyran-2-yl(Thp) portion and Jones oxidation of the resulting alcohol 8 gave the amino acid 9 which was cyclized. Final N-debenzylation of 10 provided the natural alkaloid 11 . Only two protective groups were needed in this synthesis. The reaction of N-alkyl-lactams with organometallic reagents is discussed.     

Enzyme-Catalyzed Synthesis of O-Glycopeptide Building Blocks

Abstract

In 1988, MOSBACH et aL¹ reported the synthesis of a-D-mannopyranosy1-L-serine and Q -D-N-acetylgalactosamino-L-serine by reversing the hydrolytic activity of a -mannosidase from jack beans and a -N-acetylgalactosaminidase from beef liver, respectively. The yields in these equilibrium-controlled syntheses² using high concentrations of monosaccharide and serine were highly dependent on the enzyme concentration and ranged from 5 to 10 percent in both cases.     

Synthesis of Anellated Pyranose Derivatives on the Basis of Levoglucosenone

ABSTRACT

1,6-Anhydro-2-(dicyanomethylene)-2,3-dideoxy-4-S-ethyl-4-thio-β-D-erythro-hexopyranose (1) reacted with tosyl azide or sulfur and triethylamine to furnish the 5-aza-10, 11-dioxatricyclo[6.2.1.0^2,6]undeca-2(6),3-diene-3-carbonitrile 2 and the 10,11-dioxa-5-thiatricyclo[6.2.1.0^2,6]undeca-2(6),3-diene-3-carbonitrile 3, respectively. The reactions of 1 with arylisothiocyanates furnished the 11,12-dioxa-5-thiatricyclo[7.2.1.0^2,7]dodeca-2(7),3-diene-3-carbonitriles 4 and 5. 3 underwent cyclization with triethyl orthoformate and ammonia or hydrazine hydrate to afford the 5,7-diaza-14,15-dioxa-9-thiatetracyclo[10.2.1.0^2,10.0^3.8]pentadecatetra(tri)enes 7 and 8, respectively.     

Magnetic Anisotropy of Dichlorobis(η5‐cyclopentadienyl) Complexes of Vanadium,Niobium, and Tantalum

Abstract. The magnetic behavior of the mononuclear nd¹ systems MCp₂Cl₂ (M = V⁴⁺[3d¹], Nb⁴⁺[4d¹], Ta⁴⁺[5d¹], space group P2₁/c, pseudosymmetry of the molecules C_2v) deviates from pure single ion spin magnetism on account of ligand field effect (H_lf), spin‐orbit coupling (H_so), and intermolecular spin‐spin exchange interactions (H_ex). For both VCp₂Cl₂ and NbCp₂Cl₂ excellent adaptations to the measured susceptibility data were obtained (2 K ≤ T ≤ 300 K) on the basis of spectroscopic data (lf, so) and cooperative metal–metal interactions (ex) of antiferromagnetic nature [molecular field model (mf)]. For TaCp₂Cl₂ experimental term structure data are not available. Therefore, Jørgensen's spectroscopical series (g‐factor of the central ion) was applied to extrapolate the data set for TaCp₂Cl₂. H_lf, H_so, and H_ex (antiferromagnetic) increase in the order 3d¹ → 4d¹ → 5d¹ leading, with rising atomic number of the metals, to a distinct enhancement of the magnetic anisotropy. At 4 K the μ_eff components μ_eff,y (oriented perpendicular to the cg–M–cg plane; “cg” = center of gravity of the Cp ring), μ_eff,z (oriented along the twofold pseudoaxis), and μ_eff,x are 1.73, 1.69, 1.68 (V), 1.73, 1.62, 1.59 (Nb), and 1.71, 1.59, 1.49 (Ta). While μ_eff,y is independent of T, both μ_eff,z and μ_eff,x decrease with decreasing T.