Ring-opening dynamics of jadomycin A and B and dalomycin T

[structure: see text] A novel oxazolone ring-opening and interconversion process between the two jadomycin diastereomeric forms has been characterized by NMR spectroscopy. An analogue, dalomycin T, has been isolated for the first time and does not undergo interconversion.     

Synthetic studies on jadomycins: synthesis of dimethyljadomycin A

Dimethyljadomycin A was synthesized as the first example for the construction of 8H-benzo[b]oxazolo[3,2-f]phenanthridine skeleton.     

Synthesis, NMR and X-ray structure analysis of macrolide aglycons

Macrolide aglycons (E)-9-hydroxyimino-6-O-methylerythronolide A (4), 9a-aza-9-deoxo-9,9-dihydro-9a,11-O-dimethyl-9a-homoerythronolide A (5) and 9a-aza-9-deoxo-9,9-dihydro-9a-homoerythronolide A (6) were prepared by multistep syntheses. A conformational study of these new macrolide aglycons was performed using single crystal X-ray crystallography to gain information about the solid state, while a combination of NMR spectroscopy and molecular modelling was employed to study the solution structures. The crystal structures were found to be stabilised by a complex network of hydrogen bonds and van der Waals interactions. To some extent, the same building motif of infinite molecular chains held together by O?CH···O hydrogen bonds was present in the crystal structure of all three compounds. Thorough analysis and comparison of the obtained solid state structures with their solution counterparts showed no significant differences between them, confirming the constrained flexibility of the macrocyclic ring. Moreover, in all three compounds, in both solution and solid state, the macrolactone ring adopts energetically more favoured folded-out conformations.     

Synthesis and properties of oligonucleotides with iodo-substituted aromatic aglycons: investigation of possible halogen bonding base pairs

Ab initio calculations of halogen bond energies of artificial base pairs constructed between iodinated aromatic nucleobase mimics and nitrogen-containing acceptor molecules such as pyridine and imidazole suggest that modified base pairs are converted to optimized planar base pairs with weak Delta E values of -0.19 to -3.93 kcal/mol. To evaluate the contribution of halogen bonding toward duplex stabilization of such modified nucleobase mimics introduced into artificial base pairs, we synthesized three C-nucleoside analogues 1-3 with several iodinated aromatic rings and an imidazole nucleoside derivative 4 and incorporated them into oligodeoxynucleotides. Hybridization studies of modified oligodeoxynucleotides incorporating iodoaromatic bases showed their unique universal base-like ability; however, no indication of halogen bond formation was observed. A more sophisticated design is required for the development of new base pairs stabilized by halogen bonding.     

Synthesis and studies of catechol-containing mycobactin S and T analogs

The syntheses of catechol-containing mycobactin S and T analogs are described. These analogs incorporate a catechol-glycine moiety in place of the phenol-oxazoline of the naturally occurring mycobactins S and T. Studies indicated that the new siderophore analogs bind iron, and promote the growth of a number of microbes, especially strains of mycobacteria, as expected.     

Synthesis of 3-benzoyl-4-benzylfurans structural related to furolignans

Abstract

Furolignan-type natural products, possessing important biological properties, have been synthesized from a commercially available furan. The elaborated synthetic strategy is based on an innovative Friedel-Crafts reaction starting from an alcohol or a carboxylic acid and triflic anhydride as promoter. Through this synthetic strategy, furolignans having two different aryl groups have been obtained. The products have been evaluated for their antimicrobial properties on Gram positive and Gram negative bacteria, in order to compare their biological activities with those of natural analogues.     

Synthesis and structural anomaly of xyloketals-unique benzoxacycles: A review

Xyloketals, unique bioactive compounds, isolated from mangrove fungus Xylaria sp. (no. 2508), having multiple pharmacological, therapeutic properties, have prompted enormous research on their stereochemistry, bioactivity and synthetic attempts made toward this novel family. This review brings forward a systematic and comprehensive survey of the method of both racemic and enantioselective synthesis, reactivity, and biological properties associated with the xyloketal derivatives and their analogues.     

Synthesis and structural revision of annuionone A

Annuionones (1-5), allelopathic agents isolated from Helianthus annus (sunflower), were reported to be ionone-type bisnorsesquiterepenes. However, the proposed structures for annuionones A (1), B (2) and E (5) were thought to be incorrect. Thus, we have tentatively proposed a revised structure (6) for annuionone A based on careful re-analyses of the reported spectral data. The synthesis of (±)-6 was accomplished to prove the structure of natural annuionone A as 6.     

T肽的合成:合成方法的比较研究

本文用Fmoc-及Boc-固相多肽合成法合成了T肽, 结果表明BOC法得率略高于Fmoc法, 但其纯度没有Fmoc法好, 在两种合成T肽方法中, 均得到一个副产物, 经质谱分析证明, 在BOC法中的副产物是侧链仍含有一个苄基保护的T肽; 在Fmoc法中的副产物是侧链仍含有一个叔丁基保护的T肽。     

Weight-reducing effect of Acer truncatum Bunge may be related to the inhibition of fatty acid synthase

In order to study the anti-obesity ability and inhibition towards fatty acid synthase (FAS) of the extract, a 70% ethanol extract of Acer truncatum Bunge (AT) leaves was further extracted with ethyl acetate. FAS is a very significant lipogenic enzyme, participating in energy metabolism in?vivo; it has also been observed that FAS inhibitors might be potent anti-obesity agents. Experimental results on animals showed that the extract significantly reduced food intake and adipose, and effectively controlled weight evolution. Lipogenesis inhibition might be regarded as one of the reasons for the weight control and adipose reduction by AT. The extract was further isolated using a series of column chromatography that yielded 10 known compounds. 1,2,3,4,6-Penta-O-galloyl-β-D-glucose was found to be one of the major active constituents in the extract of AT.     

Phyteumosides A and B: new saponins with unique triterpenoid aglycons from Phyteuma orbiculare L

Phyteumosides A (1) and B (2), two saponins with unprecedented triterpenoid aglycons, were isolated from the aerial parts of Phyteuma orbiculare (Campanulaceae). Their structures were elucidated by spectroscopic and chemical methods and corroborated by X-ray diffraction analyses of the aglycons obtained through enzymatic hydrolysis. The aglycon of 1 can be considered as an incompletely cyclized onoceroid or gammaceroid triterpene with two additional tetrahydropyran rings arising from oxygen bridges. Compound 2 possesses a new 17-polypodene aglycon.     

Synthesis of the sedum and related alkaloids: A personal perspective

Significant recent contributions to the synthesis of the sedum alkaloids are discussed. Related compounds, such as pinidinol, porantheridine, dumetorine and the tetraponerines are also included. The syntheses are categorised according to the key motif or chemistry employed: isoxazolidines, metathesis, asymmetric aza-Michael, heterocycle lithiation, organocatalysis, aromatic heterocycles and chiral imines.     

Synthesis of alkaloid 223A and a structural revision

[structure: see text] Synthesis of alkaloid 223A has been achieved by sequential use of our original conjugate addition reaction to enaminoesters as the key step. The proposed structure for natural 223A (A, absolute configuration unknown) was revised to B, and the relative stereostructure was determined to be 5R*,6R*,8R*,9S* by the present synthesis.     

A series of mono and diesters of itaconic acid: Synthesis and structural determination

Summary A series of mono and diesters of itaconic acid containing alkoxy and sulfide side chains of variable lengths has been synthesized. Their structures have been established on the basis of their spectral data.

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Eine Serie von Mono- und Diestern von Itaconsäure: Synthese und Strukturbestimmung

Zusammenfassung Es wurde eine Serie von Mono- und Diestern von Itaconsäure mit Alkoxy- und Sulfidseitenketten variabler Länge synthetisiert. Die Strukturaufklärung erfolgte mittels spektroskopischer Daten.

     

TheT 1 state ofp-nitroaniline and related molecules: A CNDO/S study

The nature of the lowest energy triplet state (T ₁) ofp-nitroaniline (PNA), N,N-dimethyl-p-nitroaniline (DMPNA) and nitrobenzene (NB) is reexamined using the semiempirical CNDO/S-CI method with selected parameter options. The present results indicate that in the case of theunperturbed molecules the short-axis polarized * n() triplet largely localized at the acceptor end of the molecule may lie lower in energy than the triplet manifold counterpart of the intense intramolecular charge-transferD ⁺ A ^–singlet excitation. Computations suggest, however, that polar solvents strongly stabilize the PNA and DMPNA * charge-transfer triplet relative to other excitations, whereas specific solvent hydrogen-bonded interactions stabilize the * n() triplet of NB below those of * character. These assignments allow a rationalization of phosphorescence lifetime data,T _n T ₁ absorption measurements and relative photochemical behavior.     

A new platform for NCN dimethylamino pincer complexes: Synthesis and structural studies

The reaction of 2,6-(2-{Me₂NCH₂}C₆H₄)₂C₆H₃I (2) with Pd₂(dba)₃ produced the NCN diamine pincer complex [2,6-(2-Me₂{NCH₂}C₆H₄)₂C₆H₃PdI] (3) by an oxidative addition route. The structural analysis of ligand precursor 2 revealed a syn-conformation in the solid state. Single crystal X-ray analysis of complex 3 revealed a conventional square planar geometry about the palladium center and a global C₂ symmetric structure. Variable temperature and concentration NMR spectroscopic studies of complex 3 suggest an equilibrium between 3 and the dinuclear species [{2,6-(2-{Me₂NCH₂}C₆H₄)₂C₆H₃Pd}₂μ²-I]I in CDCl₃ solution. An unusual carbonate complex [{2,6-(2-{Me₂NCH₂}C₆H₄)₂C₆H₃Pd}₃μ³-CO₃]I₃ (4) was also structurally characterized as a minor product during synthesis of 3.     

pumiliotoxins: magnetic resonance spectral assignments and structural definition of pumiliotoxins A and B and related allopumiliotoxins

Magnetic resonance spectral assignments for carbon-13 and protons of pumiliotoxin A, B and $\text{251D}$ and of related allopumiliotoxins (7-hydroxy congeners) are presented. Pumiliotoxin A and its 7-hydroxy congener allopumiliotoxin $\text{323B}$ can occur as pairs of 15-hydroxy epimers in dendrobatid frogs. Allopumiliotoxin $\text{323B'}$ and $\text{323B''}$ and allopumiliotoxin 267A (the 7-hydroxy congener of $\text{251D}$) have 7-axial hydroxy moieties. Allopumiliotoxin $\text{339A}$ and $\text{339B}$ are, respectively, the 7- axial-hydroxy and 7-equatorial-hydroxy congeners of pumiliotoxin B. Formation of ring phenyl boronides occurs only with allopumiliotoxin $\text{339B}$ which has the 7-equatorial hydroxy cis to the 8-axial hydroxy of the indolizidine ring.     

Iron-sulfur proteins: structural chemistry of their chromophores and related systems

Intensive studies of iron-sulfur proteins were begun only a decade or so ago but many biological and physicochemical data have since been accumulated and summarized^[1–5]. As a result of the very recent X-ray analyses of the structures of rubredoxin^[6], ferredoxin (Peptococcus aerogenes)^[7] and the Chromatium vinosum high potential iron protein (Hipip)^[8], it has become possible to review our understanding of the nature and function of the inorganic chromophores in these proteins; to relate these findings to ‘model’ systems of varying relevance; but of more general interest, to comment on redox processes in biological systems particularly with respect to what might be termed electron transfer—allosteric effects in metalloenzymes.