Retention keto groups

One other samandarine alkaloid, namely cycloneosamandaridine, contained a tautomeric aminocarbonyl carbinolamine system, and it was initially thought to be related to samandaridine just as cycloneosamandi-one was related to samandarone 34). However, synthetic cycloneosamandaridine with the carbinolamine formed with a C-19 aldehyde was not identical with the natural compound 36), which thus appears to have a carbinolamine formed with a 6-keto group. Retention of the original name, cycloneosamandaridine, for the natural compound would be unfortunate, since it implies the presence of the cycloneosamandione A,B ring system. The name isocycloneosamandaridine, proposed in Ref. 5, is used in this chapter (see Fig. 2). The name cycloneosamandaridine was retained for the synthetic material, which is shown in Fig. 3 it has not been reported in Nature. 

The hqnorice extract is a classical expectorant component in cough syrups. Furthermore, liquorice is used, owing to its sweet taste, in the confectionery industry and also the food industry (liquorice ice cream ). After overdosage of liquorice (more than 25 g), cortisone-effects (due to the structural similarities between cortisone and glycyrrhetinic acid, among others the 11-keto-group) are obtained oedema, salt retention, hypokalae-mia (low potassium content in blood). 

Retention of keto groups. A mixture of nonanal and cyclohexanone in methylene chloride treated with 2 eqs. MAD, and 1.1 eqs. ethylmagnesium bromide added at —78° undecan-3-ol. Y 71%. F.e., also reduction of aldehydes with r-BuLi or /-BuMgCl, s. 

Prim, alcohols from aldehydes Preferential reduction of aldehyde groups with retention of keto-groups... 

Acetone and triethylsilane heated 24 hrs. at 100 in the presence of anhydrous ZnGlg isopropoxytriethylsilane. Y 78%. F. e., also selective addition at the keto group with retention of carbon-carbon double bonds, s. R. Galas, E. Frain-net, and J. Bonastre, G. r. 251, 2987 (1960). 

The location of the hydroxy substituent in compounds like juglone and 7-methyljuglone (Fig. 18) influences the retention of these compounds. Intramolecular hydrogen bonding between the keto group and the hydroxyl substituent reduces the polarity and results in relatively high Rf values. In contrast, lawsone (Fig. 18) is strongly sorbed on the TLC layer. 

Retention data for all the Isomeric methyl oxostearates were recorded by Tulloch [926], and the elution pattern resembles that described above for the corresponding acetoxy derivatives. GC retention data for some conjugated polyenoic fatty acids with keto groups in position 4 have been recorded [334]. 

Three possible mechanisms can be postulated for formation of the oxygen-bearing centres in the macrolides and ionophores (a) retention or direct reduction of the keto group in the growing -ketoacyl chain (b) reduction followed by dehydration and stereospecific rehydration of the resulting enone or (c) multistep reduction to a fully saturated deoxygenated chain followed by aerobic oxidation. A number of studies have shown path (a) to be the predominant one. 

Reduction of vinyloxiranes The substrates are reduced rapidly by Sml2 to (E)-allylic alcohols without effect on keto, ester, or nitrile groups. Chiral substrates are reduced to optically active alcohols with complete retention of stereochemistry. 

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