Structural conversions of rhodamines in solution

A study has been made of the acidic ionization, structural conversions, and prototropic tautomerism of rhodamine chromogens in methanol and dimethyl sulfoxide, using IR, ¹³ C NMR, and electronic spectroscopy. The lactone structure has been established for the colorless form of rhodamines in DMSO. For rhodamine B in mixtures of water with DMSO, the lactone/zwitterion ratio has been estimated.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow 117975. Khar'kov State University, Khar'kov 310077. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 512–521, March, 1992.     

Commutators of singular integrals on spaces of homogeneous type

In this work we prove some sharp weighted inequalities on spaces of homogeneous type for the higher order commutators of singular integrals introduced by R. Coifman, R. Rochberg and G. Weiss in Factorization theorems for Hardy spaces in several variables, Ann. Math. 103 (1976), 611–635. As a corollary, we obtain that these operators are bounded on L ^p (w) when w belongs to the Muckenhoupt’s class A _p , p > 1. In addition, as an important tool in order to get our main result, we prove a weighted Fefferman-Stein type inequality on spaces of homogeneous type, which we have not found previously in the literature.     

The practical synthesis of a novel and highly potent analogue of bryostatin

Macrocycle 1 is a new highly potent analogue of bryostatin 1, a promising anti-cancer agent currently in human clinical trials. In vitro, 1 displays picomolar affinity for PKC and exhibits over 100-fold greater potency than bryostatin 1 when tested against various human cancer cell lines. Macrocycle 1 can be generated in clinically required amounts by chemical synthesis in only 19 steps (LLS) and represents a new clinical lead for the treatment of cancer.     

Mass spectrometric study to characterize thioisoindole derivatives of aminoglycoside antibiotics

Aminoglycoside antibiotics are widely used to treat serious Gram-negative and Gram-positive bacterial infections. The lack of a UV chromophore presents a problem in the analysis of aminoglycosides. Derivatization with 1,2-phthalic dicarboxaldehyde (OPA) in the presence of a thiol made it possible to introduce a UV chromophoric thioisoindole moiety. A qualitative mass spectrometry study was carried out to confirm the molecular identity of the products formed. The conditions described earlier to derivatize gentamicin and kanamycin yielded products in which all primary amino groups are fully derivatized. On the other hand, with tobramycin and amikacin, there was also formation of incompletely derivatized products that contained one thioisoindole group less than the fully derivatized product. This study has therefore brought an additional insight into the nature of the OPA-aminoglycoside derivatives studied.     

Compressible dimer model for the phase trasition in SnCl2·2H2O

The basic dimer model for the phase transition in the layered hydrogen-bonded crystal SnCl₂·2H₂O is modified by the inclusion of elastic effects. This compressible dimer model, in which the dimer excitation energy depends on lattice volume, is used to explain the anomalous specific-heat data close to the transition temperature.     

Total synthesis of polycavernoside A, a lethal toxin of the red alga Polycavernosa tsudai

[structure: see text] Two approaches to the synthesis of the aglycon 120 of polycavernoside A (1) were developed, only one of which was completed. The successful "second-generation" route assembled the aglycon seco acids 102 and 106 via Nozaki-Hiyama-Kishi coupling of aldehyde 70, prepared from methyl (S)-3-hydroxy-2-methylpropionate (72) and (S)-pantolactone (73), with vinyl bromide 71. The latter was obtained from a sequence which commenced from the silyl ether 24 of 3-hydroxypropionaldehyde and entailed cyclization of (Z)-zeta-hydroxy-alpha,beta-unsaturated ester 82. Regioselective Yamaguchi lactonization of trihydroxycarboxylic acids 102 and 106 and subsequent functional-group adjustments led to macrolactone 120, to which the fucopyranosylxylopyranoside moiety was attached. Stille coupling of the glycosidated aglycon 128 with dienylstannane 129 furnished polycavernoside A in a synthesis for which the longest linear sequence was 25 steps. The overall yield to lactone 120 was 4.7%.     

Average peptide score: a useful parameter for identification of proteins derived from database searches of liquid chromatography/tandem mass spectrometry data

The quantity and variable quality of data that can be generated from liquid chromatography (LC)/mass spectrometry (MS)-based proteomics analyses creates many challenges in interpreting the spectra in terms of the actual proteins in a complex sample. In spite of improvements in algorithms that match putative peptide sequences to MS/MS spectra, the assembly of these lists of possible or probable peptides into a 'correct' set of proteins is still problematic. We have observed a trend in a simple relationship, derived from standard database search outputs, which can be useful in assessing the quality of a MS/MS-based protein identification. Specifically, the ratio of the protein score and number of non-redundant peptides, or average peptide score (APS), can facilitate initial filtering of database search results in addition to providing a useful measure of confidence for the proteins identified. This parameter has been applied to results from the analysis of multi-protein complexes derived from pull-down experiments analyzed using a two-dimensional LC/MS/MS workflow. In particular, the complex list of protein identifications derived from a drug affinity pull-down with immobilized ampicillin and an E. coli lysate was greatly simplified by applying the APS as a filter, allowing for facile identification of the penicillin-binding proteins known to interact with ampicillin. Furthermore, an APS threshold can be used for any data sets derived from electrospray ionization (ESI)- or matrix-assisted laser desorption/ionization (MALDI)-MS/MS experiments and is also not specific to any database search program.     

Intramolecular Nonbonded Interactions Between Oxygen and Group VIA Elements: An Ab Initio Molecular Orbital and Density Functional Theory Investigation of the Structures of HX—CH2—COOH (X=S,Se, and Te)

Ab initio molecular orbital and density functional methods have been used to study the potential energy surfaces of the substituted acetic acids HX—CH₂—COOH, where X is one of the Group VIA Chalcophiles S, Se, or Te. The various conformers adopted by these compounds provide information regarding the energetic importance of nonbonded and hydrogen bonding interactions involving oxygen atoms with different hybridizations. Density functional and ab initio molecular orbital methods yield similar structural and energetic trends for these compounds. Calculations show that the structure of the lowest-energy conformer of each of these acids has the X—C—C—O backbone substantially twisted from planarity, similar to that previously observed for the corresponding aldehydes, HX—CH₂—CHO. In the twisted acid structures the shortest distance is within about 0.1 Å of the sum of the X and O van der Waals radii, which reduces overcrowding of the lone pairs of electrons on these atoms. In conformers where the heavy atom backbone is planar, one of the distances is significantly shorter than the sum of the van der Waals radii, and the total molecular energy of these conformers is higher than that of the twisted forms. The variation of X—H vibrational frequencies among conformers reflects the extent of X—H hydrogen bonding, and indicates that formation of this hydrogen bond is not the dominant factor in determining the lowest-energy conformation. When X is oxygen (HO—CH₂—COOH), the lowest-energy conformer is also nonplanar, whereas for the corresponding aldehyde, HO—CH₂—CHO, the lowest-energy conformer is a planar structure with C_S symmetry. The conformational preferences of these simple species provide reference points for inter- and intramolecular interactions in more complex systems of biological interest.