Synthesis and Wagner-Meerwein Rearrangement of 9-(a-Hydroxyalkyl)xanthenes to 10-Substituted Dibenz[b,f]oxepins: Scope, Limitations and ab initio Calculations S y n t h e s i s a n d W a g n e r -M e e r w e i n R e a r r a n g e m e n t o f 9 -( a -H y d r o x y a l k y l ) x a n t h e n e s Abstract: A series of 9-(hydroxy)alkyl xanthenes 5 was prepared in good yields via: (a) addition of 9-lithioxanthene to functionalized acetaldehydes, or, via a new method, (b) addition of carbanions to xanthene-9-carbaldehyde. A practical and efficient synthesis was found for the latter. Under acidic catalysis, the majority of the addition products underwent Wagner-Meerwein rearrangement to give either the corresponding, 10-substituted dibenz[b,f]oxepin 6 or the xanthenylid-9-ene b-elimination product 7. The first WagnerMeerwein rearrangement of a homobenzylic cyanohydrin is reported. The dibenz [b,f]oxepins are potential precursors of neuroactive substances. To rationalize product distribution, and probe the scope of the new rearrangement, ab initio quantum mechanical calculations have been carried out on products and transition states in selected cases.

Intact chloroplasts isolated from leaves of eight species of 16:3 and 18:3 plants and chromoplasts isolated from Narcissus pseudonarcissus L. flowers synthesize galactose-labeled mono-, di-, and trigalactosyldiacylglycerol (MGDG, DGDG, and TGDG) when incubated with UDP- [6-3H]galactose. In all plastids, galactolipid synthesis, and especially synthesis of DGDG and TGDG, is reduced by treatment of the organelles with the nonpenetrating protease thermolysin. Envelope membranes isolated from thermolysin-treated chloroplasts of Spinacia oleracea L. (16:3 plant) and Pisum sativum L. (18:3 plant) or membranes isolated from thermolysin-treated chromoplasts are strongly reduced in galactolipid:galactolipid galactosyltransferase activity, but not with regard to UDP-Gal:diacylglycerol galactosyltransferase. For the intact plastids, this indicates that thermolysin treatment specifically blocks DGDG (and TGDG) synthesis, whereas MGDG synthesis is not affected. Neither in chloroplast nor in chromoplast membranes is DGDG synthesis stimulated by UDP-Gal. DGDG synthesis in S. oleracea chloroplasts is not stimulated by nucleoside 5'-diphospho digalactosides. Therefore, galactolipid:galactolipid galactosyltransferase is so far the only detectable enzyme synthesizing DGDG. These results conclusively suggest that the latter enzyme is located in the outer envelope membrane of different types of plastids and has a general function in DGDG synthesis, both in 16:3 and 18:3 plants.The 16:3 plants differ from 18:3 plants by the occurrence of cis-7,10,1 3-hexadecatrienoic acid in MGDG4 of the chloroplasts (7,16,17,24 doplasmic reticulum. These lipids consequently are called eukaryotic (9,14,17,30). In 16:3 plants, the two galactolipids MGDG and DGDG are present in both the prokaryotic and eukaryotic configuration (3,16,20), and thus must be derived partially from plastid and partially from reticular diacylglycerol residues. The galactolipids of 18:3 plants, however, are found only in the eukaryotic configuration.In the membranes of chloroplasts and other plastids, MGDG and DGDG are formed by stepwise galactosylation of diacylglycerol (7,21,25,29). It has been suggested that pro-and eukaryotic galactolipid molecules might be synthesized in plastids by different sets of enzymes, the prokaryotic galactolipids being formed in the inner and eukaryotic lipids in the outer envelope membrane (2, 3,17,18). A different localization of UDP-Gal:diacylglycerol galactosyltransferase (MGDG synthase) in the outer envelope membrane of pea (a 18:3 plant) chloroplasts (4), but in the inner envelope membrane of spinach (16:3 plant) chloroplasts (2, 12), was considered evidence for such a hypothesis. Moreover, two distinct enzymatic activities have been proposed for the biosynthesis of DGDG. In 1961, Ferrari and Benson (8) suggested a pathway of DGDG synthesis in which MGDG is galactosylated by UDP-Gal. Using extracts from pea leaves, indeed, Siebertz and Heinz (26) succeeded in measuring DGDG formation from the two precursors UDP-Gal and MGDG. Lat...

A new convenient and scalable synthesis of phenylacetic acids has been developed via the iodide catalyzed reduction of mandelic acids. The procedure relies on in situ generation of hydroiodic acid from catalytic sodium iodide, employing phosphorus acid as the stoichiometric reductant.

The prescribing of diamorphine to opiate dependent drug users remains rare in the United Kingdom. Not all eligible doctors seek a licence to prescribe, and not all those with licences actually prescribe it. There is no clear consensus on who should be treated with diamorphine and in what way.

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