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Dedicated to Professor Dr. A . Eschenmoser on the occasion of his 60th birthday (6.V1.85)The hypothesis which explains the diastereoselectivity of the 1,3-dipolar cycloaddition of the N-glycosylnitrones 1-3 leading to the 5,s-disubstituted isoxazolidines 4 6 on the basis of a kinetic anomeric effect predicts that nucleophiles should add to N-glycosylnitrones with a high degree of diastereoselectivity. To test this prediction, the nucleophilic addition of lithium and potassium dialkylphosphites to the crystalline (Z)-nitrone 11, prepared from oxime 9 and (benzy1oxy)acetaldehyde has been examined. The addition of lithium phosphites gave the N-glycosyl-N-hydroxyaminophosphonates 12-16 (d. e. 78-92%) in high yields (Scheme 4). The addition of potassium phosphites showed a much lower diastereoselectivity. Glycoside cleavage, hydrogenolysis, and dealkylation of 12-16 gave (+)-(S)-phosphoserine (+)-19 (34-45 % from 9).Its absolute configuration was confirmed by an X-ray analysis of the N-(3,3,3-trifluoro-2-methoxy-2-phenylpropionyl) derivative 24. Similarly, the crystalline nitrone 25 gave the N-glycosyl-N-hydroxyaminophosphonate 26, which was transformed into ( +)-(S)-phosphovaline (+)-31 (42% from 9). The diastereoselectivity of the nucleophilic addition and the enantiomeric purity of ( + )-31 were determined by the analysis of the derivative 30 (d.e. 92%) and 32 (d.e. 93%), respectively. The addition of lithium diethyl phosphite to the nitrone 33, prepared in situ, gave the N-glycosyl-N-hydroxyaminophosphonate 34 (41 %;d.e. 91 YO), which was transformed in (+)-(S)-phosphoalanine (+)-37 (21 Sb from 9).

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Parallel synthesis of focused compound libraries for hit confirmation and lead optimization are certainly important drivers for shortening the lead discovery phase in the pharmaceutical and crop protection industries. In this article we show with permission of Roche and Syngenta three real case studies where Polyphor synthesized focused libraries for lead validation and optimization using high-throughput parallel synthesis and purification techniques. The three examples differ significantly in the synthetic strategies which were employed as well as in the chemical complexity of the final products. A multigeneration approach towards insecticidal triazines, the application of a sequential three-component reaction towards insecticidal and fungicidal thiazoles and finally a multistep synthesis approach of advanced building blocks followed by a two-step final derivatization towards novel antiviral N-hydroxy-indolin-2-ones are presented. In all cases 100–200 analogues were synthesized using parallel synthesis in solution followed by purification of the final products by parallel flash or high-throughput (unattended) HPLC (coupled to MS) within four months. Promising biological results were obtained in all three cases.

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