Ab initio Study of the Keto-Enol Equilibriumof Malonaldehyde

 The mechanism of the keto-enol tautomerism of malonaldehyde was studied by ab initio methods using 6-21G^** and 6-311G^** basis functions at the HF level. Two separate mechanisms were examined: through-space proton transfer in the ω-shaped form and through-space proton transfer in a sickle-shaped form obtained from the ω form by rotation. The transition state structure of the ω form is non-planar, whereas that of the sickle form is planar. The sickle form is connected with a 2^nd order saddle, indicating that there should exist a lower energy barrier, i.e. that the through-bond mechanism may be preferred. The calculated energy barriers of keto-enol tautomerism for the sickle form is twice as high as those for the omega form.     

Cyclopentenone Annulation of 2-Oxocycloalkane-1-carbonitriles

Phase-transfer alkylation of the 2-oxocycloalkane-l-carbonitriles 1a and 1b with ethyl 4-bromo-3-methoxy-2-butenoate ( 2 ), followed by deprotection and base-catalyzed cyclization gave the annulated cyclopentenones 5a and 5b , respectively, in high overall yields (Scheme 1). Stereoselective catalytic hydrogenation of 5b followed by de-ethoxycarbonylation afforded 14-oxo-cis-bicyclo[10.3.0]pentadecane-l-carbonitrile ( 7 ). Treatment of 7 with LiN(i-Pr)₂ in THF gave the known synthetic muscone precursor 8 (Scheme 2). The tricyclo[10.4.0.0^1,15]hexadecan-14-one ( 14 ) was prepared from 7 in 5 steps by a reaction sequence proceeding without affecting the chiral centres (Scheme 2). The structure of 14 was established by X-ray structure analysis (Figure).     

Chordal varieties of Veronese varieties and catalecticant matrices

It is proved that the chordal variety of the Veronese variety is projectively normal, arithmetically caulay, and its homogeneous ideal is generated by the 3×3 minors of two catalecticant matrices. Results are generalized to the catalecticant varieties Gor_≤(T) witht ₁=2. Translated from Itogi Nauki i Tekhniki, Seriya Sovremennaya Matematika i Ee Prilozheniya. Tematicheskie Obzory. Vol. 56. Algebraic Geometry-9, 1998.     

Synthesis of macrocyclic imides by one-step ring enlargement

By one-step ring-enlargement reaction with isocyanates, 2-cyano- and 2-(ethoxycarbonyl)-substituted cycloalkanones are converted into macrocyclic imides.     

Synthese von Makrocyclen durch Ringerweiterung von 14gliedrigen cyclischen Imiden

Synthesis of Macrocyles by Ring Enlargement of 14-Membered Cyclic Imides In the presence of a base, cyclododecanone derivative 2 , activated in α-position by an allyloxycarbonyl group, underwent ring enlargement with isocyanates to give 14-membered imides (Schemes 1–3). Cleavage of the activating group gave new 14-membered imides which could be transformed by further ring-enlargement reactions into new macrocyclic compounds.     

Effects of newcastle disease virus glycoproteins on the structural and thermal behaviour of 1,2-dihexadecyl-sn-glycero-3-phosphatidylcholine lipid membranes under osmotic stress conditions

The interaction of hem agglutininneuraminidase (HN) and fusion (F) glycoproteins with swollen vesicles of 1,2-dihexadecyl-sn-glycero-3-phosphatidylcholine (DHPC) was investigated under transition from gel to fluid phase. X-ray studies of the structure of lipid/HN-F mixtures in normal and swollen vesicles have shown that the lamellar bilayer structure predominate in the gel and liquid crystalline phases. A swollen lipid phase, in which the mean repeat distance of lipid bilayers is larger than in the other phases was found. The nature of this phase is similar to the anomalous bilayer swelling reported in literature. The presence of HN and F in the vesicles led to the coexistence of structures with low and high lamellar order, showing larger repeat distance in comparison with the pure lipid. This finding was attributed to the increase in the lipid bilayer thickness due to the HN-F included in the free water layer. The thermal behaviour of the system was not affected by the vesicle swelling. The data showed the existence of gel and liquid crystalline lamellar phases and changes in lipid/HN-F specific heats, mainly due to the concentration effect of the HN-F and its location in the free water layer.