QSAR and mode of action studies of insecticidal ecdysone agonists†

A series of our SAR and QSAR studies of synthetic moulting hormone agonists, dibenzoylhydrazines (DBH), exhibiting insecticidal/larvicidal activity are reviewed in this article. We prepared a number of analogues where various substituents are introduced into the two benzene rings of DBH and measured their biological activity using various biological systems. Larvicidal activity was against larvae of the rice stem borer Chilo suppressalis and the moulting hormone activity was in terms of the stimulation of N-acetylglucosamine incorporation in a cultured integument system of the same insect species. Binding affinity to the ecdysone receptor was assayed with intact Sf-9 cell lines in which the ADME processes are negligible as well as using receptor proteins obtained by in vitro translation of the responsible cDNA cloned from cell-free preparation of integumentary tissue of C. suppressalis. Variations in the biological activity indices were either correlated between two types of activity or correlated using physicochemical molecular and substituent parameters in terms of the classical QSAR. Comparisons among correlations and with recently revealed X-ray crystallographic findings clearly indicate the physicochemical meaning of parameters significant in the correlation equations to help understanding molecular mechanism of the moulting hormonal action.     

Quantitative analysis of urinary phospholipids found in patients with breast cancer by nanoflow liquid chromatography–tandem mass spectrometry: II. Negative ion mode analysis of four phospholipid classes

Analysis was performed on four different categories of phospholipids (phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidic acid (PA)) from urine in patients with breast cancer. This quantitative analysis was conducted using nanoflow liquid chromatography–electrospray ionization–tandem mass spectrometry (nLC-ESI-MS-MS). This study shows the profiling of the phospholipids (PLs) that can be identified by the negative ion mode of MS. A previous study (Kim et al. Anal. Bioanal. Chem. 393:1649, 21) focused on only two PL classes: phosphatidylcholines (PCs) and phosphatidylethanolamines (PEs) and were identified by positive ion mode. PLs were extracted by lyophilization of 1 mL of urine from both healthy normal females and breast cancer patients before and after surgery. Separation of PLs was performed by nLC followed by structural identification of PLs using data-dependent collision-induced dissociation. A total of 34 urinary PL molecules (12 PSs, 12 PIs, four PGs, and six PAs) were quantitatively examined. Among the four PL categories examined in this study, most PL classes showed an increase in the total amounts in the cancer patients, yet PIs exhibited some decreases. The present study suggests that the lipid composition found in the urine of breast cancer patients can be utilized for the possible development of disease markers, when the analysis is performed with negative ion mode of nLC-ESI-MS-MS.      

Cu2+/BH−4 reduction system: Synthetic utility and mode of action

Cu²⁺/BH⁻₄ offers a mild, method of reduction for aromatic and aliphatic tertiary nitro groups. Its mode of action has been studied, in comparison with related reagents, by deuterium isotope experiments.     

Cyclization of N-allylthiourea derivatives by the action ofα-chloronitrosoalkanes

A convenient method is proposed for obtaining difficultly available derivatives of 2-amino-5-chloromethyl-2-thiazoline by the cyclization of N-allythioureas under the action of-chloronitrosoalkanes. It is assumed that the reaction proceeds as a halogenophilic process leading to the intermediate formamidinesulfenyl chloride which is rapidly and selectively cyclized with the formation of 2-amino-2-thiazoline derivatives.Institute of Physiologically Active Substances, Russian Academy of Sciences, Chernogolovka 142432, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 381–384, March, 1998.     

Synthesis and biological evaluation of enantiomeric rhamnose analogues of the antitumour agent spicamycin—is the mode of action by modification of N-linked glycoproteins?

The synthesis of both enantiomers of dodecyl rhamnospicamycin 2a and 2b, a rhamnose analogue of the naturally occurring combinatorial library spicamycin 1, are derived from l-rhamnose and methyl α-d-mannopyranoside, respectively. The l-(+)-enantiomer 2a containing an l-rhamnose fragment is shown to be highly cytotoxic towards human myeloma cells with an IC₅₀=120 nM, whereas the d-(−)-enantiomer 2b, based on a d-mannose structure, shows no significant cytotoxicity. The analogue 16, in which the nucleotide base fragment has been replaced by a simple methoxy group, has no cytotoxicity. Initial studies towards clarifying the mechanism of anti-cancer action of spicamycin analogues are reported.     

Intramolecular cyclization of S-phenyl 3-arylpropynethioates by the action of Brønsted and Lewis acids

Russian Journal of Organic Chemistry -     

Aromatase — its mechanism and mode of action of some inhibitors — a molecular modelling perspective

The mechanism for the final step of Aromatase (AR) and the mode of action of some steroidal and non-steroidal inhibitors are studied with a molecular modelling approach involving consideration of the positioning of the P-450 heme with respect to the substrate backbone — the “substrate-heme complex”.This study suggests that Aminoglutethimide (AG) type compounds mimic the steroid C(17) carbonyl and not the C(3) carbonyl group as previously suggested by other workers. It also shows that inhibitors based on pyridine ligands such as 3-(4′-pyridyl)-3-ethyl piperidine-2,6-dione (PYG) utilise the steroid C(3) carbonyl binding region, thereby agreeing with other workers. Consideration of the orientation of the R and S enantiomers of PYG shows a reversal of results previously reported. By using inhibitors bound to the “substrate-heme complex”, and data from previous studies of derivatives of androstenedione, reasons for the differences in activity of enantiomers of AG, PYG, N-octyl-3-(4′-pyridyl)-3-ethyl piperidine-2,6-dione and 10-thiiranylestr-4-ene-3,17-dione, as well as other potent and less potent inhibitors, are suggested.The study also considers the three mechanisms of aromatisation, as proposed by Wright and Akhtar, from a geometric point of view and concludes that only a ferroxy radical is involved in all three steps of aromatisation, and not the mixture of both ferroxy and peroxy as previously postulated. An alternative theoretical mechanism, which circumvents the production of the CHO radical for the final step of aromatisation, is suggested.     

Synthesis of the ‘southern’ tripeptide of Cyclomarins A and C having novel anti-tuberculocidal mode of action

The synthesis of the ‘southern’ tripeptide of Cyclomarins A and C has been described which includes two unusual amino acids. The unusual amino acids have been synthesized and coupled with l-alanine to obtain the tripeptide.     

A new mode of stereochemical control revealed by analysis of the biosynthesis of dihydrogranaticin in Streptomyces violaceoruber Tü22.

A class of Streptomyces aromatic polyketide antibiotics, the benzoisochromanequinones, all shows trans stereochemistry at C-3 and C-15 in the pyran ring. The opposite stereochemical control found in actinorhodin (3S, 15R, ACT) from S. coelicolor A3(2) and dihydrogranaticin (3R, 15S, DHGRA) from S. violaceoruber Tü22 was studied by functional expression of the potentially relevant ketoreductase genes, actIII, actVI-ORF1, gra-ORF5, and gra-ORF6. A common bicyclic intermediate was postulated to undergo stereospecific reduction to provide either the 3-(S) or the 3-(R) configuration of an advanced intermediate, 4-dihydro-9-hydroxy-1-methyl-10-oxo-3-H-naphtho[2,3-c]pyran-3-acetic acid (DNPA). Combinations of the four ketoreductase genes were coexpressed with the early biosynthetic genes encoding a type II minimal polyketide synthase, aromatase, and cyclase. gra-ORF6 was essential to produce (R)-DNPA in DHGRA biosynthesis. Out of the various recombinants carrying the relevant ketoreductases, the set of gra-ORF5 and -ORF6 under translational coupling (on pIK191) led to the most efficient production of (R)-DNPA as a single product, implying a possible unique cooperative function whereby gra-ORF6 might encode a "guiding" protein to control the regio- and stereochemical course of reduction at C-3 catalyzed by the gra-ORF5 protein. Updated BLAST-based database analysis suggested that the gra-ORF6 product, a putative short-chain dehydrogenase, has virtually no sequence homology with the actVI-ORF1 protein, which was previously shown to determine the 3-(S) configuration of DNPA in ACT biosynthesis. This demonstrates an example of opposite stereochemical control in antibiotic biosynthesis, providing a key branch point to afford diverse chiral metabolic pools.     

Hydrogenation of arenes by the RhCl3-aliquat® 336 catalyst: Part 3. Selective reduction of polycyclic compounds

Acenaphthylene, fluorene, anthracene, phenanthrene, benz[a]anthracene, pyrene, fluoranthene, benzo[c] phenanthrene and some of their derivatives were shown to undergo partial hydrogenation in the presence of the RhCl₃-Aliquat^® 336 catalyst in a highly selective manner. Olefinic double bonds were found to be hydrogenated prior to aromatic moieties. In linear aromatic molecules, only the terminal rings are reduced. In phenanthrene the C₉-C₁₀ bond and in pyrene the C₄-C₅ linkage are the only ones to be affected. Benz [a] anthracene is converted exclusively into 7,8,9,10-tetrahydrobenz[a]anthracene. Benzo[c] phenanthrene is hydrogenated to give primarily the 5,6-dihydro derivative. Chlorine and bromine substituents were found to undergo hydrogenolysis when attached to the reacting moieties, but usually remain unaffected when located on non-reacting aromatic rings.     

Polymerizability of cycloalkenes in “living” ring-opening metathesis polymerization initiated by Schrock complexes: 3. effect of monomer structure.

The kinetics of the “living” and “controlled” ring-opening metathesis homo- and copolymerization of several cycloalkenes initiated by Mo-based Schrock complexes were investigated in the context of a general study devoted to the relation between the monomer structure on its reactivity. First, the polymerizability of these monomers was measured as a function of both their ring strain and their bulkiness. In a second part, the intrinsic reactivity of both the monomers and the corresponding active centers was evaluated from the determination of the rate constants of homopropagation and the various reactivity ratios. The steric hindrance created by the monomer substituents has only a small effect on the intrinsic reactivity of the cycloalkene. The latter mainly depends on the ring strain exactly as does the polymerizability. Steric crowding around the acyclic double bonds of the polymer chain is another factor affecting the reactivity of the active propagating centers; the latter is indeed found to depend on the capability of these acyclic double bonds to compete with the double bond of the cyclic monomer for the complexation to the transition metal.     

Vibrational analysis of crystalline diketopiperazine—II. Normal mode calculations

Based on our Raman and i.r. [1] data and assignments for DKP and five of its isotopic derivatives, we have refined an intramolecular force field in a non-redundant basis. This analysis shows that the cis peptide group may be best differentiated from the trans by the presence of an NH out-of-plane bend mode in the 800 cm⁻¹ region. Several atom—atom potentials have been evaluated for their ability to explain observed lattice frequencies and internal mode splittings. Observed splittings in CO stretch modes can be accounted for by dynamical charge transfer and transition dipole coupling interactions.     

Deciphering the mode of action of the processive polysaccharide modifying enzyme dermatan sulfate epimerase 1 by hydrogen–deuterium exchange mass spectrometry

Distinct from template-directed biosynthesis of nucleic acids and proteins, the enzymatic synthesis of heterogeneous polysaccharides is a complex process that is difficult to study using common analytical tools. Therefore, the mode of action and processivity of those enzymes are largely unknown. Dermatan sulfate epimerase 1 (DS-epi1) is the predominant enzyme during the formation of iduronic acid residues in the glycosaminoglycan dermatan sulfate. Using recombinant DS-epi1 as a model enzyme, we describe a tandem mass spectrometry-based method to study the mode of action of polysaccharide processing enzymes. The enzyme action on the substrate was monitored by hydrogen–deuterium exchange mass spectrometry and the sequence information was then fed into mathematical models with two different assumptions of the mode of action for the enzyme: processive reducing end to non-reducing end, and processive non-reducing end to reducing end. Model data was scored by correlation to experimental data and it was found that DS-epi1 attacks its substrate on a random position, followed by a processive mode of modification towards the non-reducing end and that the substrate affinity of the enzyme is negatively affected by each additional epimerization event. It could also be shown that the smallest active substrate was the reducing end uronic acid in a tetrasaccharide and that octasaccharides and longer oligosaccharides were optimal substrates. The method of using tandem mass spectrometry to generate sequence information of the complex enzymatic products in combination with in silico modeling can be potentially applied to study the mode of action of other enzymes involved in polysaccharide biosynthesis.     

Observation of a New 2§ Excited Electronic State of SF by Resonance-Enhanced Multiphoton Ionization Spectroscopy

The (2+1) resonance-enhanced multiphoton ionization (REMPI) spectrum of SF has been obtained in the single-photon wavelength region of 307-321 nm. Five vibronic bands were observed and assigned to the two-photon transitions from the ground state to a 2§ Rydberg state. The term value Te, vibrational frequency, and the rotational constant of the 2§ Rydberg state were determined. Another 2P state was observed near 312 nm.     

Fourier transform infrared isotopic study of ZnC3: identification of the ν1(a') mode

An isomer of ZnC(3) with bent structure in its (1)A(') electronic state has been detected in the products from the dual laser ablation of carbon and zinc rods that were trapped in solid Ar at ~12 K. Measurements of (13)C isotopic shifts have enabled the identification of the ν(1)(a(')) asymmetric carbon stretching fundamental at 1858.9 cm(-1). The experimental results are in good agreement with the predictions of DFT-B3LYP/6-311G(d) calculations that indicate a singlet bent isomer ground state structure with triplet linear and singlet cyclic isomers lying slightly higher in energy. This is the first optical detection of any isomer of ZnC(3).     

Structural analysis of κ-carrageenan sulfated oligosaccharides by positive mode Nano-ESI-FTICR-MS and MS/MS by SORI-CID

Structural analysis of sulfated oligosaccharides from kappa-carrageenan of up to ten residues (MW >2 kDa) was successfully carried out by positive mode nano-ESI-FTICR-MS together with MS/MS using sustained off-resonance irradiation-collision induced dissociation (SORI-CID). Glycosidic bond cleavage reactions via the B- and Y-types of fragmentation were observed and enabled complete sequencing of the oligosaccharide samples. The positions of the labile sulfate substituents were observable using SORI-CID, enabling the determination of the sequence of the sulfated residues.