The conversion of pentoses to 3,4-dihydroxyprolines

The synthesis of two naturally-occurring isomers of 3,4-dihydroxyproline is reported. l-2,3-cis-3,4-trans-3,4-Dihydroxyproline was synthesized from l-arabinose in 10 steps and 31% overall yield. The same series of reactions was employed to convert l-xylose to l-2,3-trans-3,4-trans-3,4-dihydroxyproline. Orthogonally protected versions of these amino acids were produced on gram scale, en route to the free amino acids, and these will serve as versatile intermediates in peptide synthesis. This synthetic strategy involved Nα-Fmoc protection and protection of the C3 and C4 secondary alcohols as methoxyethoxymethyl (MEM) ethers.