In vivo transformations of artemisinic acid in Artemisia annua plants

Artemisinic acid labeled with both ¹³C and ²H at the 15-position has been fed to intact plants of Artemisia annua via the cut stem, and its in vivo transformations studied by 1D- and 2D-NMR spectroscopy. Seven labeled metabolites have been isolated, all of which are known as natural products from this species. The transformations of artemisinic acid—as observed both for a group of plants, which was kept alive by hydroponic administration of water and for a group, which was allowed to die by desiccation—closely paralleled those, which have been recently described for its 11,13-dihydro analog, dihydroartemisinic acid. It seems likely therefore that similar mechanisms, involving spontaneous autoxidation of the Δ^4,5 double bond in both artemisinic acid and dihydroartemisinic acid and subsequent rearrangements of the resultant allylic hydroperoxides, may be involved in the biological transformations, which are undergone by both compounds. All of the sesquiterpene metabolites, which were obtained from in vivo transformations of artemisinic acid retained their unsaturation at the 11,13-position, and there was no evidence for conversion into any 11,13-dihydro metabolite, including artemisinin, the antimalarial drug, which is produced by A. annua. This observation led to the proposal of a unified biosynthetic scheme, which accounts for the biogenesis of many of the amorphane and cadinane sesquiterpenes that have been isolated as natural products from A. annua. In this scheme, there is a bifurcation in the biosynthetic pathway starting from amorpha-4,11-diene leading to either artemisinic acid or dihydroartemisinic acid; these two committed precursors are then, respectively, the parents for the two large families of highly oxygenated 11,13-dehydro and 11,13-dihydro sesquiterpene metabolites, which are known from this species.     

Field ionization mass spectrometry—IV. Isotopically labeled heptanals

The field ionization (FI) mass spectra of n-heptanal and a series of deuterium labeled analogs have been studied, with the objectives of initiating systematic investigations of reaction mechanisms of FI produced ions and to permit comprison with those found for other ionization processes. It is now recognized that FI ions have: (a) lower average internal energies and (b) shorter residence times than similar ions generated by electron-impact (EI), and the possibility exists of H/D-randomization occuring in ions formed by desorption from the emitter, by unimolecular decomposition close to the emitter and by either ‘fast’ or ‘slow’ metastable decompositions. In this study only the peak shifts of normal ions could be utilized; accurate mass measurements of all major ions revealed elemental compositions similar to EI. A site-specific McLafferty rearrangement gave the base peak at m/e 44 ([C₂H₄O]^+.), although the apparently complementary ion at m/e 70 ([C₅H₁₀]^+.) arose in a less specific process. Ions at m/e 43 ([C₃H₇]⁺) and 71 ([C₅H₁₁]⁺ 80%; [C₄H₇O]⁺ 20%) were apparantly generated without significant H/D-scrambling. Of special interest was the observation of the rearrangement ion at m/e 86 ([C₅H₁₀O]^+.) caused by loss of C-2 and C-3 as C₂H₄, as found for EI. It is concluded that at least in this system, decomposing molecular ions formed: (a) in the gas phase extremely close to the emitter and/or (b) on the emitter surface, have lifetimes sufficiently short to preclude complete H/D randomization. The results also provide evidence for common fragmentation mechanisms for heptanal molecular ions at both the low end and the high end of the energy distribution.     

Cytoskeletal elements of chick embryo fibroblasts revealed by detergent extraction.

Treatment of chick embryo fibroblasts with 0.5% Triton X-100 extracts most of the cell protein, leaving an organized part of the cell structure attached to the tissue culture dish. This "Triton cytoskeleton" consists largely of intermediate-sized filaments and bundles of microfilaments. SDS polyacrylamide gel electrophoresis reveals that this cytoskeleton is made up of three main proteins. One protein component is 42,000 daltons and co-migrates with muscle actin. The other two components are 52,000 and 230,000 daltons and remain quantitatively associated with the cytoskeleton during the detergent extraction. The possible identity of these three protein components and their organization into a supramolecular structure is discussed.     

Kinetic studies in mass spectrometry—IV. The [M — Cl] reaction in substituted chlorobenzenes and the question of molecular ion isomerization.

The [M]⁺˙ → [M ? Cl]⁺ reaction in a series of m- and p-X substituted chlorobenzenes has been studied, utilizing a simple kinetic approach, comparison of metastable ion relative abundances, and by measurement of ionization and appearance potentials. All evidence obtained is consistent with rearrangement prior to cleavage in the molecular ions, in which substituent position becomes effectively randomized. These findings are related to known hydrogen randomization reactions occurring in either the molecular ion or [M ? Cl] ion of chlorobenzenes. Mechanisms involving carbon scrambling via such species as ionized benzvalenes or prismanes, or ring-opening to isomeric acyclic molecular ions in which hydrogen randomization might occur can be entertained, but mechanisms involving simple hydrogen shifts in the intact benzene ring appear less likely.     

Study of the Reactions of Platinum Macrocyclic Complex Ions with Free Radicals Formed by Pulse Radiolysis of Aqueous Media

The near-diffusion-controlled reactions of hydroxyl radical, hydrated electron, and hydrogen atom with platinum macrocyclic complex ions in aqueous media have been studied using pulse radiolysis in conjunction with UV-visible absorption and conductivity detection. The hydrated electron and hydrogen atom react with trans-[Pt(cyclam)(Cl)(2)](2+) where cyclam is 1,4,8,11-tetraazacyclotetradecane to yield platinum(III) transients that exhibit intense absorption peaks in the 280-300 nm region; however in the case of the H-atom, the reaction involves a competition between chloride abstraction and a minor process, suggested to be attack on the organic ligand. The platinum(III) products are kinetically labile toward loss of chloro ligands, but these reactions are reversible in the presence of added KCl. The reactions of hydroxyl radical with [Pt(cyclam)](2+) and with [Pt(tmc)](2+), where tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, lead to platinum(III) intermediates absorbing in the 250-300 nm region. Depending on the presence or absence of added KCl and on the pH, the platinum(III) cyclam systems can react to form a product(s) exhibiting absorption peaks near 330 and 455 nm, and this species is proposed to be a long-lived amidoplatinum(III) complex. In support of this proposal is the observation that the tmc system does not give rise to a similar visible-absorbing product. The interrelations of the cyclam-based transients through acid-base, chloro-substitution and water-elimination processes are discussed.     

Microwave spectra of transient species — cyclopentadienone

The microwave spectrum of the main isotopic species of cyclopentadienone has been measured and assigned. The rotational constants imply an essentially planar geometry and that the ring is rather “fatter” than the analogous ring in fulvene.The dipole moment, derived from Stark-effect measurements, is 10.4 × 10^?30 C m (3.13 D). A vibrational satel- lite spectrum, which, from its inertial defect, corresponds to an out-of-plane vibration has also been assigned.The life time of cyclopentadienone under our spectroscopic conditions is approximately 15 sec.     

Synthesis of 2– and 4-amino-1,5-naphthyridines

The structure of the product obtained from the reaction of potassium amide in liquid ammonia on 1,5-naphthyridine has been identified as 4-amino-1,5-naphthyridine by comparison with a known sample. The 2-amino isomer was not detected in the mixture. The NMR spectra for 2-and 4-amino-1,5-naphthyridine along with the corresponding chloroisomers are described.     

A pharmaceutical information manager's viewpoint on R & D information resource management

An overview of the environment (from my perspective) related to information resource management in pharmaceutical R & D has been presented. Some notions of organizational preference (functional), employee selection (chemist turned information scientist), automation (user friendly, cost effective), and the value of project teams (information transfer) have been noted. Difficulties associated with keeping our innovative tools sharp were observed. Finally, we noted that our bottom line--productivity--should first consider what is useful (effectiveness) and then learn how to do it well--efficiency. Success in the management of information resources depends on the proactive delivery of information packets which find their way into problem solving and decision support for scientists or line managers.     

The de novo design of median molecules within a property range of interest

Summary In this paper an application is presented of the median molecule workflow to the de novo design of novel molecular entities with a property profile of interest. Median molecules are structures that are optimised to be similar to a set of existing molecules of interest as an approach for lead exploration and hopping. An overview of this workflow is provided together with an example of an instance using the similarity to camphor and menthol as objectives. The methodology of the experiments is defined and the workflow is applied to designing novel molecules for two physical property datasets: mean molecular polarisability and aqueous solubility. This paper concludes with a discussion of the characteristics of this method.     

Substitution with retention in organoboranes and utilization of the phenomenon for a general synthesis of pure enantiomers

Organoboranes, readily available via the hydroboration of unsaturated organic compounds, exhibit a remarkable versatility in their reactions. The boron atom in these organoboranes can be readily converted into a wide variety of organic groups under very mild conditions, providing simple versatile syntheses of organic compounds. Exploration of these substitution reactions reveal that, with rare exceptions, the organoboranes transfer the alkyl group to other elements of synthetic interest with complete retention of stereochemistry. Recently we have discovered a method of synthesizing essentially optically pure organoborane intermediates. These optically active alkyl groups attached to boron can also be transferred with complete retention of optical activity. Consequently, it is now possible to achieve by a rational synthesis the preparation of almost any optically active compound with a chiral center, either R- or S-, in essentially 100% enantiomeric excess.