Methyloxime derivatives

Bromine trifluoride is very efficient in converting various carbonyl groups into CF2 moieties via azine, hydrazone, and O-methyloxime derivatives.122... 

Shimada et al. [29] described the conversion pregnenolone and its 3-stearate ester into 3-acetate-20-methyloxime and 20-methyloxime derivatives, respectively. 20-fold improvement in the detection limit was reported by Liu et al. [30] as a result of the derivatization of oxosteroids into their oximes. 16P-hydroxystanozolol was derivatized with phei rlboronic acid to reduce the fragmentation in MS-MS [31]. Williams et al. [32] reported derivatization of 2- and 4-hydroxyestradiol with... 

Synthesis from o-glucose Various methods have been reported for the synthesis of trehazolamine (3) from carbohydrate precnrsors such as D-glucose. Thus, the 4,6-benzylidene derivative 10, easily prepared from D-glucose, was converted quantitatively to the respective open chain 0-methyloxime derivative (Scheme 2) Subsequent oxidation ... 

The simultaneous g.c.-(e.i.)m.s. analysis of sugars (aldoses, ketoses, sugar acids, oligosaccharides and alditiols), carboxylic acids and phosphoric acid as their pertrimethylsiylated oxime derivatives has been optimized and applied to the analysis of over 40 such components in apple varieties. G.c.-m.s. analysis of carbohydrates as their acetylated 0-methyloxime derivatives was particularly useful for application to glycoconjugates of plant origin. ... 

Product Characterization. The products of sunflower leaf hydroperoxide lyase are cw-3-hexenal and 12-oxo-c/.y-9-dodecenoic acid. Analysis of the methoxylamine derivative of the volatile C -aldehyde product by GC-MS showed that it had a mass spectrum and GC retention time identical to that of the methyloxime derivative of commercial c/>3-hexenal, with a small molecular ion at m/z 127 and a large M-29 peak at m/z 98. In contrast, the methyloxime derivative of commercial rra/ij-2-hexenal had a large molecular ion at m/z 127 and a smaller M-29 peak (m/z 98), and it eluted later on the chromatogram. The oxoacid product, 12-oxo-ci>9-dodecenoic acid, was characterized as its methyloxime, methyl ester derivative. The compound had a molecular ion at m/z 255, with a larger M-31 fragment at m/z 224. Its GC retention time was earlier than that of a methoxylamine, methyl ester derivative of 12-oxo-rra/2j-10-dodecenoic acid standard, which had an M-31 fragment (m/z 224) smaller than the molecular ion at m/z 255. 

A direct preparation of selectively protected derivatives of 3-hydroxyquinoline-2-carboxylates 55 was found through use of a modified Friedlander condensation employing the readily accessible O-methyloxime 54 <95JCX3(60)7369>. 

The final coupling reaction of l-cyclopropyl-6-fluoro-7-chloro-l,4-dihy-dro-4-oxo-l,8-naphthyridine-3-carboxylic acid (7a) and 4-( er -butoxycarbo-nylaminomethyl)pyrrolidin-3-one-0-methyloxime (15a) proceeds according to the methods described by Sanchez et al. [13], Domogala et al. [16], and Kimura et al. [17], followed by acid hydrolysis to afford gemifloxacin, 7 - (4 - (aminomethyl) - 3 - (methoxyimino)pyrrolidin -1 - yl) -1 - cyclopropyl - 6 -fluoro-4-oxo-l,4-dihydro[l,8]naphthyridine-3-carboxylic acid and other corresponding derivatives, according to Scheme 5. 

Kahane et al. [169] first oxidized vanillylmandelic acid, after its extraction from urine by the action of sodium periodate, to vanillin. The vanillin was then converted into the methyloxime by reaction with methoxylammonium chloride and finally silylated. The recovery of the total procedure, including extraction from urine, is said to be minimally 95%, with the resulting derivative being highly specific for the compound under analysis. The GC analysis was performed on QF-1 as stationary phase. 

To deduce the location of the double bond within the lipid backbone, the mixture (500 ng) was subjected to consecutive bisthiomethylation of the alkene85 and O-methyloxime formation (Equation 3). GC—MS study of the fragmentation of these derivatives (e.g., see 31, derived from 24) allowed simultaneous determination of the cleavage site (between C24 and C25) and of which portion contained the original ketone (i.e., the odd versus even mass fragments of 17 3 and 426 for 31). All of the monounsaturated lipid ketones had the alkene in the same downstream location in other words, they varied in the number of methylene units between the ketone and alkene functional groups but were constant in their -octyl terminal alkyl moiety. The four most major components (24, 25, 27, and 28) were prepared by chemical synthesis and used to confirm their identity in the natural pheromone and their pheromonal activity both alone and in admixtures. 

MS and GC-MS. A variety of derivatives have been used to protect labile functional groups of the free prostaglandins prior to gas chromatography and direct fragmentation in GC-MS. The 9,11-/3-ketol grouping of the E series is particularly sensitive in vapour phase analysis and commonly 0-methyloxime TMS ether derivatives or O-methyloxime acetates have been employed in GC-MS (e.g. [426]). An alternative approach is to dehydrate the ketol under controlled conditions to the more stable enone analogues of the B series [427,428]. The cyclic n-butylboronate of the 9,11-diol in the F series when used with methyl ester TMS ethers confers good GC properties and some simplification in... 

Single-peak sugar derivatives which allow the resolution of sugar constituents in pectin include the trimethylsilylated methyloximes (52), acetylated aldononitriles (53), trimethylsilylated alditols T54), and acetylated alditols (51.). A comprehensive review article on GLC of sugars has been published (26). 

Developments in capillary columns for GLC have improved the resolution of the individual components with a concomitant reduction of elution times. Neeser and Schweizer (1984) have separated the 0-methyloxime acetates of several sugars using a fused-silica Carbowax 20M capillary column. Although alditol acetates can be separated by capillary GLC (Blakeney et al., 1982), this method is more suitable for separating complex mixtures of partially methylated alditol acetates derived from meth-ylation analysis. It has been reported that phthalic esters interfere with the determination of alditol acetates by GLC (Dudman and Whittle, 1976) on conventional packed columns. This problem can be overcome to some extent by the use of capillary columns with polar phases (Henry et al.,... 

Fig. 11.4.4. Separation of oxime derivatives of saccharides. Chromatographic conditions column, polar-bonded amino column (Lichrosorb NH2) mobile phase, acetonitrile-water (80 20) detection, UV at 220 nm. Peaks are O-methyloximes of 1, D-glucose 2, D-maltose 3, D-cellobiose 4, D-maltotriose. Reproduced from Chen and McGinnis (1983), with permission.

The O-methyloximes of several aldoses have been examined in solution by C-n.m.r. and by g.l.c. and the authors conclude that the 0-methyl oximes exist as acyclic modifications. Those derived from simple aldoses existed as the anfi-isomer, whereas those derived from 2-deoxyaldoses existed as anti- and jyn-mixtures.The oxime of D-glucose, however, exists as a mixture of the syn- and anft-forms and the two pyranose forms. All four isomers have been separated by t.l.c. and identified spectroscopically. ... 

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