This article explores recent advances in the design and engineering of materials wholly or principally constructed from peptides. We focus on materials that are able to respond to changes in their environment (pH, ionic strength, temperature, light, oxidation/reduction state, presence of small molecules or the catalytic activity of enzymes) by altering their macromolecular structure. Such peptide-based responsive biomaterials have exciting prospects for a variety of biomedical and bionanotechnology applications in drug delivery, bio-sensing and regenerative medicine.

Peptide-based stimuli-responsive biomaterials

Macrolactonizations in the Total Synthesis of Natural Products

Gold(III) Salen complex-catalyzed synthesis of propargylamines via a three-component coupling reaction.

Current perspectives on the mechanism of action of artemisinins

A catalytic enantioselective syn-1,4-bromolactonization of conjugated (Z)-enynes was reported. Diastereomeric ratios >20:1 and up to 99% enantiomeric excesses were observed. Di-, tri-, and tetra-substituted bromoallenes were prepared together with lactone heterocycles efficiently and stereoselectively. Preliminary investigations suggest that the chiral catalyst may serve as a bifunctional reagent by interacting with both a carboxylic acid nucleophile and NBS electrophile.

Enantioselective bromolactonization of conjugated (Z)-enynes.

Halo- and selenolactonisation: the two major strategies for cyclofunctionalisation

Artemisinin (1) and its analogues have been well studied for their antimalarial activity. Here we present the antimalarial activity of some novel C-9-modified artemisinin analogues synthesized using artemisitene as the key intermediate. Further, antileishmanial activity of more than 70 artemisinin derivatives against Leishmania donovani promastigotes is described for the first time. A comprehensive structure-activity relationship study using CoMFA is discussed. These analogues exhibited leishmanicidal activity in micromolar concentrations, and the overall activity profile appears to be similar to that against malaria. Substitution at the C-9beta position was shown to improve the activity in both cases. The 10-deoxo derivatives showed better activity compared to the corresponding lactones. In general, compounds with C-9alpha substitution exhibited lower antimalarial as well as antileishmanial activities compared to the corresponding C-9beta analogues. The importance of the peroxide group for the observed activity of these analogues against leishmania was evident from the fact that 1-deoxyartemisinin analogues did not exhibit antileishmanial activity. The study suggests the possibility of developing artemisinin analogues as potential drug candidates against both malaria and leishmaniasis.

Structure-activity relationships of the antimalarial agent artemisinin. 8. design, synthesis, and CoMFA studies toward the development of artemisinin-based drugs against leishmaniasis and malaria.

Progress in the development of peroxide-based anti-parasitic agents.

Semi-synthetic derivatives of the anti-malarial drug artemisinin hold great promise in the search for an effective and economical treatment of chloroquine-resistant forms of malaria. Unfortunately, synthetic functionalization of the artemisinin skeleton is often tedious and/or impractical. We seek to utilize 7β-hydroxyartemisinin, obtained from microbial transformation, as a semi-synthetic precursor for the synthesis of novel 7β-substituted artemisinin anti-malarial agents. Here we employ liquid cultures of Cunninghamella elegans as a means for the rational and economical bioconversion of artemisinin to 7β-hydroxyartemisinin in 78.6% yield. In addition, there were three other bioconversion products: 7β-hydroxy-9α-artemisinin (6.0%), 4α-hydroxy-1-deoxoartemisinin (5.4%), and 6β-hydroxyartemisinin (6.5%).

Transformation of artemisinin by Cunninghamella elegans

Transformation of the anti-malarial drug artemisinin by the fungi Eurotium amstelodami and Aspergillus niger were investigated. Cultures were grown in sucrose/malt broth with artemisinin for 14 days and extracted with ethyl acetate. Extracts were characterized by liquid chromatography. Two metabolites from each fungal extract were isolated and identified using mass spectrometry and nuclear magnetic resonance. 5β-hydroxyartemisinin and 7β-hydroxyartemisinin were isolated in 63 and 32% yields, respectively, from the extract of E. amstelodami, and 80 and 19%, respectively, from the extract of A. niger.

K. M. Muraleedharan

Papers

Halo- and selenolactonisation: the two major strategies for cyclofunctionalisation

Structure-activity relationships of the antimalarial agent artemisinin. 8. design, synthesis, and CoMFA studies toward the development of artemisinin-based drugs against leishmaniasis and malaria.

Progress in the development of peroxide-based anti-parasitic agents.

Transformation of artemisinin by Cunninghamella elegans

Microbial transformation of artemisinin to 5-hydroxyartemisinin by Eurotium amstelodami and Aspergillus niger