Chemistry

Flavones were prepared using a one-pot procedure starting from the corresponding 2 0 -hydroxyacetophenones. The latter were treated with 3 equiv of aroyl chloride in wet K 2 CO 3 /acetone (1% w/w water) to afford a good yield of flavone and a smaller amount of 3-aroylflavone. Evidence was obtained that the reaction proceeds via a triketone intermediate. When the reactants were heated in 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and pyridine, the 3-aroylflavone was obtained exclusively. Use of a stoichiometric amount of aroyl chloride afforded only the corresponding flavone.

1~,25-Dihydroxyvitamin D3 (1,25) is a structurally unique steroid hormone because it not only possesses the complete 25-hydroxycholesterol side chain, but most notably, it possesses a seco-B triene structure (it lacks a B-ring and is usually depicted in a non-steroidal, extended conformation). In contrast, the classical steroid hormones possess a truncated side chain (progesterone, cortisol, and aldosterone) or no side chain (estradiol and testosterone) and they all possess the fully intact ABCD steroid rings. These structural differences render the seco-B-steroid 1,25 considerably more conformationally flexible. Since 1,25 is now known to target a myriad of tissues where specific interactions occur to produce an array of biological responses, it is of interest to determine whether different topologies of 1,25 (resulting from different conformational orientations of 1,25) are necessary to interact effectively at the different target sites. The array of biological responses include both non-genomic and genomic effects and there is considerable promise for the efficacy of 1,25 analogs as chemotherapeutic agents in a variety of human disease states. For the non-genomic calcium transport response of transcaltachia, the finding that two 6-s-cis locked analogs, la,25dihydroxyprevitamin D3 (pre-l,25) and l~,25-dihydroxylumisterol 3 (1,25-Lumi), are equipotent to 1,25, points strongly to the involvement of the 6-s-cis conformer of 1,25 as the biologically active conformer. Since there is a continuum of easily interconvertible 6,7-single bond conformers of the seco-B ring available to 1,25, conformational minima (either local or global) may have little to do with the manner in which 1,25 is bound to receptor. For the genomic calcium transport response, and for other genomic (or non-genomic) effects, there is no clear evidence whether the steroidal (s-cis) or non-steroidal (s-trans) conformer of 1,25 is involved. In order to address this matter further, efforts are underway to evaluate other conformationally locked analogs of 1,25 which might mimic either the planar 6-s-trans-l,25 or some intermediate conformer between it and the planar-6-s-cis form.

This work discusses the application of an Artificial Intelligence (AI) technique called Qualitative Reasoning (QR) coupled with the Qualitative Process Theory (QPT) ontology to model, simulate and explain chemical behaviours of reaction mechanisms. We have tested the new approach on two types of organic mechanisms under nucleophilic substitution reaction. This paper describes one specific type of the mechanisms called SN1 to demonstrate how the qualitative models can be constructed for chemical processes such ...

Boesenbergia rotunda is a herb from the Boesenbergia genera under the Zingiberaceae family. B. rotunda is widely found in Asian countries where it is commonly used as a food ingredient and in ethnomedicinal preparations. The popularity of its ethnomedicinal usage has drawn the attention of scientists worldwide to further investigate its medicinal properties. Advancement in drug design and discovery research has led to the development of synthetic drugs from B. rotunda metabolites via bioinformatics and medicinal chemistry studies. Furthermore, with the advent of genomics, transcriptomics, proteomics, and metabolomics, new insights on the biosynthetic pathways of B. rotunda metabolites can be elucidated, enabling researchers to predict the potential bioactive compounds responsible for the medicinal properties of the plant. The vast biological activities exhibited by the compounds obtained from B. rotunda warrant further investigation through studies such as drug discovery, polypharmacology, and drug delivery using nanotechnology.

Cyclization of a variety of chalcones to flavanones catalyzed by 1 mol% phosphomolybdic acid (PMA) supported on silica as a mild, efficient, and reusable catalyst was carried out in high yields. PMA-SiO 2 is an efficient, inexpensive, and green catalyst which gave high conversion yields and could be recycled up to three times without significant loss in activity.

The conversion mechanism of b-carotene to vitamin A has been a topic of much discussion for many years since the ®rst proposal of central cleavage mechanism, which was soon challenged by arguments supporting the eccentric cleavage mechanism. Inconclusive evidences have led to the proposal that the conversion of b-carotene does take place through both these mechanisms, possibly by different oxygenase enzymes at different locations in the body. In order to have further insight and better understanding of the cleavage mechanism, molecular mechanics calculations were performed on several cis-and transconformations of b-carotene at different polyene portion. The results indicated a series of relatively low energy cis-conformers in addition to the all trans-conformer with lowest energy conformation being the cis-C9 H ±C10 H double bond (E 46.46 kcal/ mol in water) which could act as the possible starting conformer for the reaction. The molecular mechanics (MM) energy of various cyclic peroxide structures was also carried out and the results seem to support the formation of vitamin A via a systematic degradation of b-carotene. q