Total synthesis of d-(+)-biotin

A total synthesis of d-(+)-biotin is described starting from d-(+)-glucosamine using acyliminium chemistry.     

2-(2-Selenocyanic acid ethyl ester)-1H-benz[de] isoquinoline-1,3-(2H)-dione, synthesis photophysics and interaction with bovine serum albumin: a spectroscopic approach

The compound 2-(2-selenocyanic acid ethyl ester)-1H-benz[de] isoquinoline-1,3-(2H)-dione (SEBID), a ubiquitous, bioactive naphthalimide derivative is expected to possess an anticancer, anti-tumor and other important therapeutic activities of significant potency with low systematic toxicity. In this paper, the synthesis of the compound, photophysics of the newly prepared naphthalimide derivative and its interaction with model transport protein Bovine serum albumin (BSA) have been reported using the absorption and steady state fluorescence spectroscopic techniques exploiting the intrinsic fluorescence emission properties of BSA as a probe. Interaction of this organoselenium compound in different dioxane-water mixtures with increase in the polarity of the medium has been studied spectroscopically. Interaction of SEBID with BSA leads to a dramatic decrease in the fluorescence intensity of BSA, which suggests the binding of SEBID with the tryptophan residue of BSA. Furthermore, different thermodynamic parameters for SEBID-BSA interaction have been calculated. Rationalization of the data has been attempted, particularly in relation to prospective applications in the biomedical research.     

Preface

The fifth CBRATEC (V Congresso Brasileiro de Análise Térmica e Calorimetria) conference was held in April 02–05, 2006 in Poços de Caldas, MG. One third of the 370 participants was graduates and Ph.D. students well representing the continuous interest in thermal analysis among Brazilian researchers. The structure of conference was characteristic and refreshing, since every morning one of the leading Brazil thermoanalysts held an opened teaching course especially for the representatives of the young generation. After then plenary lecturers and keynote speakers (J. Rouquerol, Cs. Novák, D. Burlett, M. Suchyta and A. Riga) occupied the podium. The afternoon sessions consisted of mainly short lectures and poster exhibitions; both provided excellent possibility for the Ph.D. students to introduce their scientific work. The scope of conference covered practically all aspects of thermal analysis. Since 1998, when the first CBRATEC conference was held, the participation of young scientists and the organization of teaching courses played essential role for them. As an effort to increase international experiences, the universities pay continuous attention to foreign language education (first of all English), so the communication between the invited international researchers, the representatives of the instrument companies and the domestic conference attendants became much more efficient in recent years. During the conference the new Executive Committee was elected. Prof. Valter José Fernandes Junior was elected as President of ABRATEC supported by the members of the Executive (Jivaldo do Rosário Matos (Vice-President), Massao Ionashiro, Lázaro Moscardini D’Assunção, Clóvis Augusto Ribeiro, Elias Yuki Ionashiro, Carlos Isidoro Braga, Manoel Luiz Cunha Rodrigues, Rodrigo Maciel). In recognition of his continuous cooperation for the development of thermoanalytical researches in Brazil and its scientific divulgation in Thermal Analysis, the ‘Special Award’ of ABRATEC (Brazilian Association for Thermal Analysis and Calorimetry) was presented to Prof. Csaba Novák. For their outstanding achievements in developing the international relation of ABRATEC, Honourable Membership of the Thermoanalytical Sub-Branch of the Hungarian Chemical Society was presented to Prof. Jivaldo do Rosário Matos, Massao Ionashiro, Prof. Valter José Fernandes Junior and Prof. Éder Tadeu Gomes Cavalheiro at the opening ceremony. At last but not least, according to the decision of ICTAC Council during the 13^th ICTAC (2004, Chia Laguna, Italy) Brazil was elected as the host of ICTAC 14 in 2008. The Brazilian thermoanalytical community feels extremely honored to be entrusted with the organization of the 14^thICTAC Conference that will take place in São Pedro, SP, in September 14–19, 2008, where the scientists, researchers and students, who are acting in the field of thermal analysis and calorimetry are cordially invited. The link to the conference site is www.ictac14.com.br.     

4-t-Butylphenoxo complexes of oxovanadium(V)

Summary Complexes of composition [VOCl₂(OC₆H₄Bu-t-4)] (1) and [VOCl(OC₆H₄Bu-t-4)₂] (2) have been synthesized by the reaction of VOCl₃ with equimolar and bimolar amounts, respectively, of 4-t-BuC₆H₄OSiMe₃ in CCl₄ and characterized by physio-chemical techniques. The complexes react with -hydroxyaldehydes and ketones such as 2-hydroxybenzaldehyde (salicylaldehyde, salH), and 2-hydroxy-2-phenylacetophenone (benzoin, benzH), 2-hydroxyacetophenone (hapH) and also with the potassium salt of p-chlorobenzohydroxamic acid (KBHACl) in 11 and 12 molar ratios, to yield five- and six-coordinate complexes.     

Self aggregation of binary mixtures of sodium dodecyl sulfate and polyoxyethylene alkyl ethers in aqueous solution

The mixed micelles of sodium dodecyl sulphate (SDS) with Brij35 and Brij 97 were studied separately by fluorescence measurement using pyrene as fluorescent probe. In the range of 0–1.0 mole fraction (X) of added SDS to Brij solutions, the cmc value of the mixed micelles varies from 0.085 to 8 mmol with Brij 35 and 0.04 to 8 mmol with Brij 97. The aggregation number also changes. A measure of the stability of mixed micelles is also presented. The interaction parameter ₁₂ and the chain–chain contribution parameter (B₁) are extracted from the analysis of the results. This parameter B₁ is related to the standard free energy change associated with the introduction of one ionic species into a nonionic micelle coupled with the release of one nonionic species from the micelle. The clouding behaviour of Brij 97 in the presence of SDS was investigated and the associated thermodynamic parameters of clouding were generated and discussed.     

Design and synthesis of novel fluoropeptidomimetics as potential mimics of the transition state during peptide hydrolysis

alpha-Fluoroamino acids were targeted in our ongoing efforts to design novel fluoropeptidomimetics (1) as potential protease inhibitors. alpha-Fluoroglycine derivative (2) and alpha-fluoro-beta-aminoethanethiol derivatives (3-9) were synthesized for the first time en route to obtain the peptidomimetic moiety 1. The stability of 2-9 was investigated under organic as well as aqueous conditions. The stability of 3-9 under acidic and basic conditions, the effect of substitution at C-2 position, and potential biological activities are discussed.     

Stereoselective synthesis of (−)-microcarpalide

A highly convergent and efficient synthesis of (−)-microcarpalide, a 10-membered lactone displaying remarkable microfilament disrupting activity is described. Ring-closing metathesis and Sharpless asymmetric dihydroxylations are the key steps. Our strategy highlights the application of novel hydroxy lactone precursors for the stereoselective synthesis of (−)-microcarpalide.     

Reactions of aromatic ketones with 3-mercapto-1,2-propanediol. Synthesis of cis- and trans-2-alkyl-2-aryl-(1,3-oxathiolane-5-methanols and 1,3-dioxolane-4-methanethiols)

Aromatic ketones react with 3-mercapto-1,2-propanediol ( 1 ) in refluxing benzene under the catalytic influence of a sulfonic acid and with azeotropic removal of water to yield a mixture comprised predominantly of cis- and trans-2-alkyl-2-aryl-1,3-oxathiolane-5-methanols 7, accompanied by lesser amounts of cis- and trans-2-alkyl-2-aryl-1,3-dioxolane-4-methanethiols 8 (up to 30%). It was discovered that 8 is the kinetic product and is isomerized by 4-toluenesulfonic acid in hot benzene to the thermodynamically more stable 7 . Under these conditions, ortho- and α-substituted aromatic ketones tend to produce more of 8 , which can be attributed to steric hindrance encountered by the thiol as it attacks the ketone. Ketalizations of 1-aryl-2-(1H-imidazol-1-yl)-1- as well as 1-aryl-2-(1,H-1,2,4-triazol-1-yl)-1-ethanones by 1 fail under these conditions, even after 24 hours of reflux in toluene. However, 1-(4-chlorophenyl)-3-(1H-imidazol-1-yl)-1-propanone and 1-(4-bromophenyl)-4-(1H-imidazol-1-yl)-1-butanone are ketalized by 1 as expected. Interestingly, the reaction of 2-bromo-4′-chloroace-tophenone with 1 produces 1-(4-chlorophenyl)-2,8-dioxa-6-thiabicyclo[3.2.1]octane. Characterization of all isomers and separation of some diastereomers is described. Nuclear Overhauser enhancement experiments are utilized to establish the stereochemistry of 1,3-oxathiolanes.     

Acceptor properties of titanium(IV) phenoxides

Summary Compounds of composition TiCl_4–n(OPh)_n · 2L (L = monodentate ligand, n = 1–4) have been prepared by the reaction of the parent titanium phenoxides (1 mol) with the ligand (2 mols) and characterized by elemental analysis, molar conductance, molecular weight and i.r. spectral studies.