Preparation of free and of specifically protected oligo[β-malic acids] for enzymatic degradation studies

Article abstract of DOI:10.1002/1099-0690(200004)2000:7<1207::AID-EJOC1207>3.0.CO;2-2

The polyanionic poly[β-(S)-malic acids] (β-PMA) occur in slime molds (myxomycetes), black yeasts and other fungi and are involved in DNA replication. In order to be able to study the cleavage mechanism of β-PMA hydrolases, we have synthesized cyclic and linear oligomers of malic acid (β-OMA) consisting of up to eight residues. To this end, fragments with three different protecting groups were prepared, with allyl ester groups on the C-terminus, TBDPS groups at the O-terminus, and benzyl ester groups at the side chains (Schemes 2, 3, 7). Selective deprotection and fragment coupling (COCl₂/C₅H₅N/CH₂Cl₂/-75 °C) gave dimers, tetramers, and octamers, either fully protected or specifically protected at the O- or C- terminus or at the side chain acid groups, and also fully deprotected oligoacids (Schemes 3-7). The new compounds were fully characterized (R(f), IR, ¹H- and ¹³C-NMR spectroscopy, mass spectrometry and elemental analysis or high-resolution electrospray mass spectrometry). Enzymatic degradation experiments with the previously prepared cyclo-tetramer, the unprotected, and the O- or C-terminally protected samples of linear β-OMAs show that the enzyme from Physarum polycephalum is an exo-hydrolase cleaving the chain from the O-terminus.