Efficient isolation of individual lipid classes is a critical step in the analysis of plasma and lipoprotein fatty acid compositions. Whilst good separations of total lipid extracts are possible by TLC, this method is time consuming and a major rate-limiting step when processing large numbers of specimens. A method for rapid separation of phosphatidylcholine (PC), non-esterified fatty acids (NEFA), cholesterol ester (CE) and triacylglycerol (TAG) from total plasma lipid extracts by solid-phase extraction (SPE) using aminopropyl silica columns has been developed and validated. Following initial separation of polar and neutral lipids, individual classes were isolated by application of solvents with increasing polarity. Recoveries for combined plasma extraction with chloroform–methanol and SPE were (%): PC 74·2 (SD 7·5), NEFA 73·6 (sd 8·3), CE 84·9 (sd 4·9), and TAG 86·8 (sd 4·9), which were significantly greater for TAG and NEFA than by TLC (P<0·001). Both GC–flame ionisation detector and GC-MS analysis of fatty acid methyl esters demonstrated that there was no cross-contamination between lipid classes. Measurements of repeatability of fatty acid composition for TAG, PC, CE and NEFA fractions showed similar CV for each fatty acid. The magnitude of the CV appeared to be related inversely to the fractional fatty acid concentration, and was greatest at concentrations of less than 1 g/100 g total fatty acids. There was no evidence of selective elution of individual fatty acid or CE species. In conclusion, this method represents an efficient, rapid alternative to TLC for isolation of these lipid classes from plasma.

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Cyclin-dependent kinases (CDKs) are regulatory proteins of the eukaryotic cell cycle. They act after association with different cyclins, the concentrations of which vary throughout the progression of the cell cycle. As central mediators of cell growth, CDKs are potential targets for inhibitory molecules that would allow disruption of the cell cycle in order to evoke an antiproliferative effect and may therefore be useful as cancer therapeutics. We synthesized several inhibitory 2,6,9-trisubstituted purine derivatives and solved the crystal structure of one of these compounds, H717, in complex with human CDK2 at 2.6 A resolution. The orientation of the C2-p-diaminocyclohexyl portion of the inhibitor is strikingly different from those of similar moieties in other related inhibitor complexes. The N9-cyclopentyl ring fully occupies a space in the enzyme which is otherwise empty, while the C6-N-aminobenzyl substituent points out of the ATP-binding site. The structure provides a basis for the further development of more potent inhibitory drugs.

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