807leaves little doubt that the acylated phenylisoserine side chain of these taxoids is synthesized via path a of Scheme I. Unexpectedly, in both experiments 1, but not 2, also showed a pronounced M + 10 peak, as well as a P + 10 satellite for the m / z 286 fragment representing the side chain. Hence, the aromatic ring of 4a and Sa must have also becn incorporated into the benzoyl group of the 1 side chain. Together with the non-incorporation of 7a this suggests the operation of a new pathway, other than the estab-lishedI3 path b/c of Scheme I, for the genesis of the benzoate moieties in this plant which proceeds from 3 via 4 (path a/d) or 4 and S (path a/e).In summary, the side chain of 1 and 2 is formed from phenylalanine via @-phenylalanine, presumably generated by an aminomutase reaction,14 followed by hydroxylation of C-2 and acylation of the nitrogen. The benzoyl moiety is also formed via @-phenylalanine and possibly phenylisoserine rather than via cinnamic acid. A&"t .We are indebted to Prof.
We report the electrochemical properties of Group 15 quaternary alkyl bistriflimide salts, which have very wide electrochemical windows (between ؉2.6 and ؊3.4 V vs. There is much current research effort focused on the use of low temperature ionic liquids in synthesis, catalysis and separations, because of their properties of negligible vapour pressure and high thermal stability.1 We are currently interested in developing ionic liquid technology for the electrodeposition of actinides of relevance to nuclear fuel processing (U and Pu). High temperature inorganic melts are currently being used for this process, 2 but the extremely high temperatures of operation (>500 ЊC), and corrosive nature of the molten solvent, makes the switch to lower temperature melts appear advantageous. However, the actinides are very electropositive metals and to achieve electrodeposition requires the use of melts with large electrochemical windows.Chloroaluminate based ionic liquids have been studied for aluminium electroplating 3 and for U and Pu electrochemical processing, 4 but the hygroscopic nature of these ionic liquids means that they are unsuitable for the bulk electrodeposition of electropositive metals. More recently, attention has focused on tetraalkyl ammonium and pyrrolidinium bis[(trifluoromethyl)-sulfonyl]amide (bistriflimide) salts, which are air and moisture stable and also possess wide electrochemical windows.5-7 These salts would appear to have wide enough electrochemical windows to allow the deposition of both U and Pu and a preliminary report has indicated that both Na and K (both more electropositive than Pu) can be electrochemically deposited8 However, despite the ongoing interest in the electrochemical processing of nuclear waste in ionic liquids 9,10 there have been no reports of f-element electrodeposition in air and moisture stable melts. In addition, there have been no investigations into the use of these ionic liquids as supporting electrolytes in organic solvent based electrochemistry.As tetraalkyl ammonium salts appeared to have the greatest cathodic stability we decided to synthesise a range of Group 15 salts of general formula [(Me) 4 X][N(SO 2 CF 3 ) 2 ] where X = N, P or As and study their electrochemical properties. These salts were prepared by standard synthetic techniques (methylation and/or metathesis reactions) and characterised by a range of analytical and spectroscopic techniques. † All of these salts are air and moisture stable and are thus suitable for industrial electrochemical application. They are also all immiscible with water. Melting points, onset of decomposition point and electrochemical window ranges as 0.2 mol L Ϫ1 electrolytes in MeCN (vs. ferrocinium/ferrocene-Fc ϩ /Fc) for all three salts are given in Table 1.All three salts have very high thermal stability, but melt at comparatively high temperatures for ionic liquids (the distinction between ionic liquid and molten salt is arbitrary but ionic liquids are usually assumed to melt below 100 ЊC). This is due to the high symmetry of t...
The Chemical Nature of Amavadin.-Mushrooms of the genus Amanita accumulate very small amounts of vanadium, an essential trace element, wherein the metal forms the complex Amavadin with (S,S)-2,2'(hydroxyimino)dipropionic acid. EPR spectra show that V(IV) is present, which is reversibly oxidizable to V(V). The V(V) complex (I) is prepared and characterized, establishing that oxidized Amavadin consists of approximately an equal mixture of the δ and λ forms of the anion. Cyclic voltammetry of Amavadin and its chemical analogues indicates that each of the V(IV)/V( V) pairs possesses a common geometry in solution. The present studies not only reveal the chemical nature of the title compound but also demonstrate that this species belongs to the group of transition metal centers in biology (e.g. blue copper, cyctochroms, iron-sulfur) which retain their structure through a one-electron redox change.-(ARMSTRONG, E. M.; BEDDOES, R. L.; CALVIOU, L. J.; CHARNOCK, J. M.; COLLISON, D.; ERTOK, N.; NAISMITH, J. H.; GARNER, C. D.; J. Am. Chem. Soc. 115 (1993) 2, 807-808; Dep. Chem., Manchester Univ., Manchester M13 9PL, UK; EN)
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