Cholesterol methyl ethers

If cholesterol esters are esterified directly and the free cholesterol is not removed prior to GC analysis, it may dehydrate to form cholestadiene on the column and this may obscure some of the C22 components [499]. Similarly, cholestadiene and cholesterol methyl ether are generated to some extent when most acidic reagents are used for transesterification, and analogous by-products are formed from plant sterols [376,494,626,835]. This does not occur with base-catalysed transesterification. Other hydrolysis products of low molecular weight from lipids, such as phytol and aldehydes, can be troublesome in some... 

Development of sterically stabilized liposomes (SSL) composed of high Tm lipids, cholesterol, and a lipopolymer, such as poly-(ethylene glycol methyl ether)-l,2-distearoyl-i n-glycero-3-phospho-ethanolamine triethyl ammonium salt (1,3-5,8,9,14,15)... 

Methyl ethers were applied firstly to the GC of cholesterols [390,391]. They are prepared by the method common for the preparation of ethers, e.g., by treatment with dimethyl sulphate or methyl iodide in the presence of potassium rert.-butoxide (cf., p. 64). Their good chromatographic properties, e.g., on SE-30 and PEGS stationary phases, are usually obtained only after further treatment with a silylating or acylating agent. 

In comparison to some of the other activation methods however, the dimethyl sulfoxide-acetic anhydride procedure has certain disadvantages. The method often requires the use of long reaction times (1 24 h), which can result in many side reactions, especially with sensitive substrates. Notable in this respect is that it is not uncommon for this procedure to result in the formation of substantial yields of the thiomethyl ethers obtained from the Pummerer rearrangement product as described above. In fact upon attempted oxidation of cholesterol with this system, the major product obtained was the corresponding (methylthio)methyl ether. Acetates may also be formed if the alcohol is unhindered. For example the sugar derivative (9) reacts under these conditions to form an enol acetate (derived from the requir carbonyl compound) in 40% yield contaminated with 30% of the acetate (10 equation S). ... 

The concept of a stable mesomeric cation cannot be inferred solely from kinetic results, but follows from analysis of reaction products, and studies of the reactions of "i-cholesterol and its derivatives. Most important was the demonstration by Winstein [35] that identical product mixtures are produced by the methanolysis of either cholesteryl tosylate or 6 trichloroacetoxy-3a,5a-cyclocholestane (15 X O-COCCls), from which it was argued that these steroids solvolyse through a common cation. Furthermore i-cholesteryl methyl ether (15 X = OMe) is converted by absolute ethanol into a mixture of i-cholesteryl ethyl ether (15 X — OEt) and cholesteryl ethyl ether [36]. i-Cholesteryl acetate (15 ... 

As silyl derivatives of oxygen-containing compounds are those most frequently used, we shall cite some examples of their application. Experimental results [83] indicate the expediency of using the trimethylsilyl ether of cholesterol and not the methyl ether, as the former yields more symmetrical chromatographic zones. VandenHeuvel et al. 

Cellulose, carboxymelhyl ether Cellulose, ethyl ether Cellulose, methyl ether Cholest-4-en-3-oI, 4-methyl- (3ot) Cholest-5-en-3-ol (3 3)- cholesterol ... 

Cholesterol, heated in dimethyl phosphite, alfords cholesteryl methyl phosphite (128), but in the presence of an acid the product is cholesteryl methyl ether. 

Steroidal methyl ethers are readily obtained from the alcohols with diazomethane and fluoroboric acid. The novel dicholesteryl acetal (132) of formaldehyde has been obtained from cholesterol, either by the anodic oxidation of a solution in aqueous acidic methanol, or by the action of sodium hydride and chloromethyl methyl ether. Dimethoxymethane undergoes partial exchange with cholesterol in acidic solution to give the methoxymethyl ether (133). ... 

Two reports of Simmons-Smith methylene addition (iodomethylzinc iodide) on to A -olefinic steroids contain several points of disagreement. The earlier paper states that cholest-5-en-3a-ol (epicholesterol) reacts readily to give the 5a,6a-methano-derivative (165). A stereospecific reaction in this sense would accord with earlier indications that a suitably placed hydroxy-group directs the approach of the reagent towards the same side of the olefinic bond. The 3/ -alcohol (cholesterol), as well as the methyl ethers and acetates of both alcohols, apparently failed to react. The later paper, by different authors, states that both unsaturated alcohols react, each giving a similar mixture of the 5a,6a- and 5) ,6/ -methano-adducts. with no evidence for control by the oxygen function. 

The jff-diethylaminoethyl esters of two substituted thyroacetic acids, LIX and LX, have been reported to be as active as L-T3 [192]. However, introduction of the )ff-diethylaminoethoxy group at the 4 -position, as in LXI, caused almost complete elimination of hypocholesterolemic activity. The 4 -methyl ether of 3,3, 5-triiodo- and 3,5-diiodo-3 -isopropylthyroacetic acid possessed hypocholesterolemic activity in the rat which was almost one-half that of L-T3. The latter two compounds exhibited a greater degree of separation between the cholesterol-lowering activity and the calorigenic or cardiotropic effects than the corresponding nonetherified substances [193]. 

Fig. 3 Effect of cholesteryl ethers in liposomes prepared with DOPC on the relative amount of glucose released (A) (x) cholesterol (o) cholesteryl methyl ether ( ) cholesteryl ethyl ether (v) cholesteryl-n-propyl ether ( ) cholesteryl isopropyl ether (A) cholesteryl butyl ether (B) (x) cholesterol (o) cholesteryl (2 -hydroxy)-3-ethyl ether ( ) cholesteryl methoxy methyl ether ( ) cholesteryl acetate.

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