Organic & Biomolecular Chemistry Blog

In this addition to OBC‘s online Organocatalysis collection, Shu-Li You and co-workers from Shanghai Institute of Organic Chemistry report a highly efficient tandem double Friedel–Crafts reaction between indoles and 2-formylbiphenyl derivatives catalysed by chiral N-triflyl phosphoramide which produces various fluorene derivatives in excellent yields and ee.

Notably, the fluorene products obtained with the chiral N-triflyl phosphoramide have the opposite absolute configuration compared to that obtained with the corresponding chiral phosphoric acid. This allows access to both enantiomers of the products by utilizing different catalysts derived from one enantiomer of binaphthol.

This paper is FREE to access for 4 weeks, and while you’re there why not have a look at the rest of the Organoncatalysis collection.

Enantioselective synthesis of fluorene derivatives by chiral N-triflyl phosphoramide catalyzed double Friedel–Crafts alkylation reaction
Shou-Guo Wang, Long Han, Mi Zeng,  Feng-Lai Sun, Wei Zhang and Shu-Li You
Org. Biomol. Chem., 2012,
DOI: 10.1039/C2OB07168A

In this HOT communication Liming Zhang and colleagues at Hunan University demonstrate how α-oxo gold carbenes generated via intermolecular oxidation of terminal alkynes are highly electrophilic. So much so that they can effectively abstract halogens from halogenated solvents. They rationalise that this carbene is more electrophilic than related rhodium species due to the presence of only one α-carbonyl group, meaning it is less capable of back bonding.

Liming Zhang et al. believe that because of this differnece α-oxo gold carbenes may provide new opportunities for methodology development. To exemplify this they show that synthetically useful chloro/bromomethyl ketones can be prepared in one-step from terminal alkynes, avoiding the problems of poor regioselectivity and over-halogenation experienced by previous methods.

Sound interesting? Why not take a look, it’s FREE to access for the next 4 weeks.

Electrophilicity of α-oxo gold carbene intermediates: halogen abstractions from halogenated solvents leading to the formation of chloro/bromomethyl ketones
Weimin He, Longyong Xie, Yingying Xu, Jiannan Xiang and Liming Zhang
Org. Biomol. Chem., 2012,
DOI: 10.1039/C2OB25235J

Gang Zhaoet al. from University of Science and Technology of China present highly diastereoselective and enantioselective [4 + 2] cycloadditions between allenoates and dual activated olefins catalyzed by bifunctional N-acyl aminophosphine catalysts.

To demonstrate the potential of the N-acyl aminophosphine catalysts in asymmetric phosphine mediated reactions, Gang Zhao et al. have prepared a range of synthetically valuable cyclohexene structures based on α-substituted buta-2,3-dienoates, which bear three contiguous chiral centers with good to excellent diastereoselectivities and enantioselectivities.

Take a look and let us know what you think!

This HOT OBC article will be free to access for the next 4 weeks.

Highly enantioselective [4 + 2] cycloadditions of allenoates and dual activated olefins catalyzed by N-acyl aminophosphines
Hua Xiao, Zhuo Chai, Dongdong Cao, Hongyu Wang, Jinghao Chen and Gang Zhao
Org. Biomol. Chem., 2012,
DOI: 10.1039/C2OB25295C

In this HOT OBC paper Jun O. Liu and co-workers at Johns Hopkins University School of Medicine report structure–activity relationship studies of two oxines, which have been previously identified as hits in a high-throughput screen aimed at finding new anti-angiogenic agents, by characterising different analogues in human umbilical vein endothelial cell assays. In addition they have determined the effects of a subset of oxine derivatives on human methionine aminopeptidase and sirtuin 1 activities in endothelial cells and screened a selection of the potent inhibitors of human umbilical vein endothelial cells against two other malignant cells.

Through this they have been able to identify new oxine derivatives that exhibit improved inhibitory activity against endothelial cell proliferation, and furthermore, have made the surprising finding that subtle structural alterations can lead to dramatic changes in the mechanism of action of the resulting derivatives.

For all the in-depth details of this study check out this paper today! It’s free to access for the next 4 weeks!

Substituted oxines inhibit endothelial cell proliferation and angiogenesis
Shridhar Bhat, Joong Sup Shim, Feiran Zhang, Curtis Robert Chong and Jun O. Liu
Org. Biomol. Chem.,  2012, 10, 2979–2992
DOI: 10.1039/C2OB06978D

In this HOT OBC paper Heiko Ihmels and colleagues at University of Siegen present the fluorimetric detection of Mg²⁺ and DNA with 9-(alkoxyphenyl)benzo[b]-quinolizinium derivatives. Although there are quite a few fluorescent probes that enable the detection of different analytes from the same class of compounds, probes that allow optical detection of different types of analytes are much rarer. In this paper Heiko Ihmels et al. show that a benzo[b]quinolizinium-benzo-15-crown-5 ether conjugate can be used for the detection of both Mg²⁺ and DNA by a significant light-up effect and with different emission wavelengths for the two different analytes.

The authors investigated the light-up mechanism by comparison with the photophysical properties of methoxyphenyl-substituted benzo[b]quinolizinium reference compounds, revealing that the position of the methoxy functionality had a significant influence on the emission properties of the donor–acceptor systems.

Find the full paper here. It’s FREE to access for the four weeks, so why not take a peek!

Fluorimetric detection of Mg²⁺ and DNA with 9-(alkoxyphenyl)benzo[b]quinolizinium derivatives
Maoqun Tian, Heiko Ihmels and Shite Ye
Org. Biomol. Chem., 2012, 10, 3010–3018
DOI: 10.1039/C2OB06948B

In this HOT OBC Communication Mark E. Graham, Richard J. Payne and co-workers probe the effect of a recently discovered post-translational modification of threinine of the assembly protein AP180, a protein which plays a crucial role in clathrin coated vesicle formation in synaptic vesicle endocytosis.

Using pull down experiments on AP180 peptide fragments they aimed to explore how binding to proteins in rat brain lysate is influenced by this modification.

Read the article to find out more about the peptides used and the effect of this modification on the affinity towards synaptic proteins.

Go on, it’s FREE to access for the next 4 weeks!

 
Synthesis and protein binding studies of a peptide fragment of clathrin assembly protein AP180 bearing an O-linked β-N-acetylglucosaminyl-6-phosphate modification
Mark E. Graham, Robin S. Stone, Phillip J. Robinson and Richard J. Payne
Org. Biomol. Chem., 2012, 10, 2545-2551
DOI: 10.1039/C2OB07139H