X-ray Analysis of 2a. Single crystals of 2a were tetrahedral, space group P43 (for the configuration shown in Figure 1) or P4lt with a -12.896 (1) Á, c = 13.773 (3) A, and d^= 1.300 g cm"1 23 for Z = 4 (CggHgjjOg, mol wt 448.47). The intensity data were measured on a Hilger-Watts diffractometer (Ni-filtered Cu Ka radiation, 0-20 scans, pulse-height discrimination). A crystal measuring approximately 0.30 X 0.6 X 0.6 mm was used for data collection. A total of 1616 reflections was measured for 0 < 57°, of which 1570 were considered to be observed [/ > 2.5»(/)]. The structure was solved by a multiple solution procedure13 and was refined by full-matrix least-squares. In the final refinement (13)

No abstract

A high performance liquid chromatographic (HPLC) method is described for separation and quantitation of 1-alkyl-3-acyl-and 1-alkyl-2-acyl-sn-glycerol, products of the detritylation reaction of 1-alkyl-2-acyl-3-trityl-snglycerol. The alkyl glycerides were separated on a 25 cm X 4.6 mm ID column packed with ~5-6 ~n silica and eluted isocratically with isooctane/isopropanol (98:2, v/v) as mobile phase. The good separation and linear refractive index (RI) detector responses using cholesterol as an internal standard indicated the applicability of the method not only for the quantitative determination of the alkylglycerols but also for their semipreparative isolation. This HPLC method shows excellent reproducibility and accuracy and is applicable to other types of glycerides such as mono-and diacylglycerols. Lipids 22, 362-365 (1987).Common precursors for the stereospecific synthesis of 1-alkyl-neutral and phospholipids are 1-alkyl-2-acyl-3trityl-sn-glycerols in which the trityl group is used to protect the hydroxyl group at the 3-position of glycerol (1,2). The next step in the synthetic sequence is removal of the trityl protecting group, under general acid catalysis, to yield 1-alkyl-2-acyl-sn-glycerols as key intermediates (Scheme 1). Acylation or phosphorylation of the latter glycerides gives the desired 1-alkyl-neutral or phosphoglyceride, respectively. Quite often, however, removal of the trityl protecting group is complicated by the concomitant migration of the 2-acyl moiety to yield the isomeric 1-alkyl-3-acyl-sn-glycerol derivative (3-6). As a consequence of this acyl rearrangement, it is necessary to separate and quantify these isomeric alkyl glycerides prior to further modification. A number of analytical methods, including column chromatography (7), thin layer chromatography (TLC) (8,9), high performance liquid chromatography (HPLC) (10,11) and gas liquid chromatography (GLC) (12) have been reported for separation and quantitative determination of mixtures of mono-, diand triacylglycerols. For the isolation of glycerides for subsequent chemical manipulation, however, HPLC methods are more advantageous than other analytical methods because of their nondestructive nature, greater range of sample capacity and ease or rapidity of opera-

No abstract

3-(Phenylsulfonyl)isoxazolines, readily obtained from alkenes by cycloaddition with benzenesulfonylcarbonitrile oxide, undergo a variety of substitution reactions. Alkyl, aryl, and acetylenic lithium reagents, cyanide, lithium or sodium alkoxides, and sodium borohydride are all useful nucleophiles. Tandem alkylations are possible with alkyllithium reagents when excess base and alkyl iodide are used. Excess base can also be used to cleave the isoxazoline ring of the initial substitution products. 3-(2-Propenyloxy)isoxazolines will undergo an aza-Claisen rearrangement on heating.