Total synthesis of (-)-kendomycin exploiting a Petasis-Ferrier rearrangement/ring-closing olefin metathesis synthetic strategy

The total synthesis of (-)-kendomycin (1), a novel macrocyclic polyketide with antibacterial and antitumor activity, was achieved in 21 steps (longest linear sequence) exploiting an effective Petasis-Ferrier union/rearrangement tactic to construct the tetrahydropyran ring, a ring-closing metathesis to generate the macrocycle, and a biomimetic quinone-methide-lactol assembly.     

The frost model and perturbation theory

Symmetry-adapted double perturbation theory is applied to the Frost model. Even when used only through zero-order in the correcting ”internal“ perturbation it gives values of average electric polarizabilities in fair agreement with experiment. If the model is extended by employing clliptical gaussians rather than spherical ones, the anisotropy of the molecular polarizability can be determined.     

Some investigations of the MP2-R12 method

Summary The MP2-R12 method was introduced by Kutzelnigg and Klopper to overcome the problem caused by truncation of the one electron basis set in correlation energy calculations at the Møller-Plesset second order level of approximation. Here, we have evaluated the integrals required by their simplest scheme using the Rys-quadrature procedure. Results are presented for Ne, H₂O, and HF using largespdf gaussian basis sets.     

Toward understanding how the lactone moiety of discodermolide affects activity

A series of simplified discodermolide analogues have been designed and synthesized in an attempt to understand the role of the lactone ring. These synthetic efforts have led to an unsubstituted butyrolactone 9 being generated, which shows improved activity over the natural product.     

Facile cobalt(III) template synthesis of novel branched hexadentate polyamine monocarboxylates

New hexadentate polyamine monocarboxylate ligands, 11-amino-9-(2-aminoethyl)-3,6,9-triazaundecanoate (tren-engly-), 12-amino-10-(2-aminoethyl)-3,7,10-triazadodecanoate (tren-tngly-) and 13-amino-11-(2-aminoethyl)-3,8,11-triazatridecanoate (tren-bngly-), were synthesized by intramolecular coupling of tetradentate tris(2-aminoethyl)amine (tren) and didentate N-([small omega]-formylalkyl)glycinates, OCH(CH2)nNHCH2CO2-, in easily and stereoselectively assembled cobalt(III) templates, p-[Co(tren){(RO)2CH(CH2)nNHCH2CO2}](O3SCF3)2, n = 1-3 (R = Me or Et). The reaction sequences comprised assembly of the template from [Co(tren)(O3SCF3)2]O3SCF3 (1) and (RO)2CH(CH2)nNHCH2CO2Et, deprotection of the pendant acetal in acid, intramolecular condensation of the resulting aldehyde with a coordinated primary amine at intermediate pH to form the imine and reduction of this by NaBH4. For n= 1, imine formation occurred exclusively at the primary amine trans to the carboxylate producing the hexadentate 11-amino-9-(2-aminoethyl)-3,6,9-triazaundeca-5-enoato (tren-enimgly-) complex, i-[Co(tren-enimgly)]Cl2.3.5H2O. In all instances, subsequent imine reduction gave the s isomer complex, exclusively. Complexes p-[Co(tren){(MeO)2CHCH2gly}](O3SCF3)2 (3), i-[Co(tren-enimgly)]ZnCl4.H2O (5), s-[Co(tren-engly)]ZnCl(4)(s-6), s-[Co(tren-tngly)]ZnCl4.H2O (s-7) and s-[Co(tren-bngly)ZnCl3]2ZnCl4 (s-8) were structurally characterized by X-ray crystallography. Charcoal-catalyzed equilibration of s-[Co(tren-engly)]Cl(2).2H(2)O dissolved in water produced the s- (s-6), p- (p-6) and t-[Co(tren-engly)]2+ (t-6) isomers in comparable amounts. p-6 and t-6 were also structurally characterized as their tetrachlorozincate and chloride salts, respectively. In base-catalyzed reactions, s-6 and t-6 each also formed p-6. Reduction of s-[Co(tren-engly)]Cl2.2H2O with (NH4)2S and acidification liberated the pentaamino carboxylic acid ligand which was isolated as the hydrochloride salt.     

Tremorgenic indole alkaloids. The total synthesis of (-)-penitrem D

A convergent, stereocontrolled total synthesis of the architecturally complex tremorgenic indole alkaloid (-)-penitrem D (4) has been achieved. Highlights of the synthesis include an efficient, asymmetric synthesis of the western hemisphere; the stereocontrolled assembly of the I-ring; discovery of a novel autoxidation to introduce the C(22) tertiary hydroxyl group, required for tremorgenic activity; union of fully elaborated eastern and western hemispheres, exploiting an indole synthetic protocol developed expressly for this purpose; and a late-stage, stereoselective construction of the A and F rings exploiting a Sc(OTf)(3-)promoted reaction cascade. The longest linear sequence leading to (-)-penitrem D (4) was 43 steps.     

Photocatalytic Umpolung of N- and O-substituted alkenes for the synthesis of 1,2-amino alcohols and diols

We report an organophotocatalytic 1,2-oxyalkynylation of ene-carbamates and enol ethers using Ethynyl BenziodoXolones (EBXs). 1-Alkynyl-1,2-amino alcohols and diols were obtained in up to 89% yield. Photocatalytic formation of radical cations led to Umpolung of the innate reactivity of the alkenes, enabling addition of a nucleophilic benzoate followed by radical alkynylation.

Photocatalytic Umpolung with organic dyes overcoming the innate nucleophilicity of enecarbamates and enol ethers for oxyalkynylation with EBX reagents to access 1-alkynyl-1,2-amino alcohols and diols.     

Principles for efficient utilization of light for mass production of photoautotrophic microorganisms

Outdoor production of microalgae could be set on a sound industrial basis if solar energy were utilized at a much higher efficiency than presently obtained. Many types of photobioreactors have been developed in the past in an attempt to answer this challenge, but their photosynthetic efficiency has been rather similar to the basically inefficient open raceway commonly used today. Efficient utilization of the oversaturating solar energy flux mandates that reactors should have a narrow lightpath to facilitate ultra-high cell densities, be maximally exposed to sunshine, and have an efficient mixing system to create strong turbulent streaming to affect dark–light cycles of the highest possible frequency.     

Self-consistent perturbation theory for conjugated molecules

The first order changes in the orbital energies of a number of hydrocarbons due to perturbations at particular atoms are given. These are useful for discussing ionization potentials, polarographic reduction and oxidation potentials, and electron affinities of heteromolecules.

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Zusammenfassung Die Änderungen erster Ordnung von Einelektronenenergien bei Störung an bestimmten Atomen werden für eine Reihe von Kohlenwasserstoffen angegeben. Sie erweisen sich als brauchbar für die Diskussion von Ionisationspotentialen, polarographischen Oxydations- und Reduktionspotentialen und Elektronenaffinitäten von Heteromolekülen.

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Résumé Les variations au premier ordre des énergies des orbitales, sous l'influence de perturbations sur des atomes déterminés, sont données pour un certain numbre d'hydrocarbures. Elles sont utiles pour la discussion des potentiels d'ionisation, des potentiels d'oxydation et de réduction polarographiques et des affinités électroniques des molécules hétéroatomiques.

     

Self-consistent perturbation theory for conjugated molecules

Since an external field produces a drift of the mobile -electrons in the plane of a conjugated molecule the electric polarizability of these molecules is anisotropic. The S.C.F. perturbation theory is used to calculate the -electron contribution to the polarizability tensor for a number of conjugated molecules. Using previous theoretical and semi-empirical values for the polarizabilities of C-C and C-H bonds the contribution is estimated and total polarizabilities for the molecules obtained as the sum of the and contributions. There is reasonable agreement between these theoretical values and the available experimental ones.

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Zusammenfassung Ein äußeres elektrisches Feld verschiebt die -Elektronen in der Molekülebene, so daß die elektrische Polarisierbarkeit von Molekülen mit konjugierten Bindungen anisotrop ist. Mittels SCF-Störungsrechnung wurde der Beitrag der -Elektronen zum Tensor der Polarisierbarkeit für eine Anzahl von Molekülen berechnet und der Beitrag des -Bindungsgerüstes aus semiempirischen Größen ermittelt. Die Übereinstimmung mit gemessenen Werten ist zufriedenstellend.

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Résumé La polarisabilité électrique des molécules conjuguées est anisotrope car un champ extérieur provoque un déplacement des électrons mobiles dans le plan moléculaire. La théorie des perturbations SCF est utilisée pour le calcul de la contribution des électrons au tenseur de polarisabilité d'un certain nombre de molécules conjuguées. En utilisant des valeurs théoriques et semi-empiriques antérieures concernant les polarisabilités des liaisons C-C et C-H on peut évaluer la contribution des électrons . Les polarisabilités totales sont obtenues comme la somme des contributions et . L'accord avec les données expérimentales disponibles est raisonnable.