Dimethylsilyl derivatives

FIGURE 6.31 Simultaneous protection of the amino and carboxyl groups of an amino acid by reaction (A) with copper(II) basic carbonate133 or acetate,134 giving the copper complex, (B) with triethyl borane giving the boroxazolidone,139 and (C) with dichlorodimethylsilane giving the dimethylsilyl derivative.138141... 

Although several advantages of dimethylsilyl (Me2HSi) ethers have been claimed,191 few examples of their use have been reported, except for the separation of cycloamyloses.133 Thus, dimethylsilyl derivatives (which are more volatile than trimethylsilyl ethers) require lower column-temperatures and have shorter retention times for example, for glucose, the per(trimethylsilyl) derivative has a retention time of 11.4 min, and the per(dimethylsilyl) derivative, 5.10 min. Both types of derivative may be analyzed on the same column, and, in certain cases, compounds inseparable as their O-trimethylsilyl derivatives may be separated as their dimethylsilyl ethers. The potential of di-methylsilylation for converting oligosaccharides into volatile derivatives should be examined. 

Thus far, there are only a few examples of the use of dimethylsilyl derivatives, but cyclo-hexa-, -hepta-, and -octa-amylose have been separated from each other by using these ethers.133... 

Cavitand 6.29 has a vase-shaped cavity that is large enough to accommodate Me2NCHO in the solid state. In solution, the most effective host is the dimethylsilyl derivative (6.28e), which has a tall, narrow cavity suitable for inclusion of linear guests such as those listed above. Compound 6.28e is prepared readily from the octol [4] resorcarene 6.3 by treatment with SiMe2Cl2. The X-ray crystal structure of the CS2 complex of 6.28e is shown in Figure 6.7, indicating clearly the neat fit of the linear... 

Of other silyl derivatives, trialkylsilyl derivatives [93], particularly for GC-MS, and dimethylsilyl derivatives [94] have been described. They are prepared by similar methods to TMS derivatives. DMS derivatives are more volatile and have shorter retention times than TMS derivatives (see Table 4.11), but they are less stable they are suitable for com-... 

Henderson et al. 1% SDS/water/methanol Enzymatic digestion SPE GC/MS (dimethylsilyl deriv) 7... 

A new method for preparing dimethylsilyl derivatives, based on silylene transfer from hexamethylsilacyclopropane to a transition-metal hydride, has been reported (equation... 

A slightly different approach was adopted by Chen and his colleagues, who protected baccatin III as its 1-dimethylsilyl derivative 4.3.I.6. Treatment of this compound with Red-Al gave a 66% yield of 4-deacetyl product 4.3.1.7, together with a small amount of dideacetyl product (188). 

The preparation of alkoxydialkylsilyl derivatives raises possibilities for varying the nature of the alcohol (and hence the alkoxy group in the final derivative) in order to induce shifts in GC elution orders for compounds containing different numbers of protic sites. The possibility of varying the nature of the alcohol could also be used to modify the selectivity of detection of a chosen analyte. Two methods of preparing alkoxy-dimethylsilyl derivatives of steroids and cannabinoids were considered by Harvey [438]. The preferred approach proceeds as follows. 

Crouholm, T. Norsten, C. Gas chromatography-mass spectrometry of carboxylic acids in tissues as their tert-butyl dimethylsilyl derivatives. J. Chromatogr. B, 1985,... 

Isopropylidene ethers of cytokinin ribosides can be made by dissolving sample in 2. 2-dimethoxypropane (30 ]ul. Fluka) to which cone. HCl (1 jul) is added. Samples are allowed to stand for 5 min at 30°C, then rapidly evaporated under a stream of N.>. These can be further converted to /m-butyl-dimethylsilyl derivatives if required [10]. 

Alternate Names l,l -(l-propene-l,3-diyl)bis[l,l,l-trimethy-Isilane] (lE)-l-propene-l,3-diylbis[trimethylsilane] (E)-prop- 1-ene-1,3-diylbis(trimethylsilane) (IZ)- 1-propene-1,3-diylbis[trimethylsilane], CAS 141291-16-9 Bis(r-butyl-dimethylsilyl) derivative (l )-l-propene-l,3-diylbis[(l,l-dimethylethyl)dimethylsilane] Bis(dimethylphenyl) derivative [[(l )-3-dimethylphenylsilyl)-1-propen-l-yl]dimethyl-silyl]-benzene other derivatives are known but less widely used. 

Corey, E.J., and A. Venkateswarlu Protection of Hydroxyl Groups as /er/-Butyl-dimethylsilyl Derivatives. J. Amer. Chem. Soc. 94, 6190 (1972). 

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