Synthesis of Monodisperse Macromolecular Bicyclic and dendritic compounds from (R)-3-hydroxybutanoic acid and benzene-1,3,5-tricarboxylic acid and analysis by fragmenting MALDI-TOF mass spectroscopy

As previously shown, oligo- and poly(β-hydroxyalkanoates) have a high tendency to form lamellar crystallites with ca. 50-Å thickness which corresponds to chain lengths of 16 units (Fig. 1). To have monodisperse model compounds, we have now prepared bicyclic derivatives with three parallel ( 27 – 29 ) or two parallel and an antiparallel chain ( 68 – 70 ) consisting of up to 16 3-hydroxybutanoate (3-HB) units. We also prepared dendritic compounds ( 71 – 75 , 82 – 85 ) containing oligo(3-HB) chains which cannot possibly be arranged as in the lamellae; the branching units were prepared from trimesic acid (= benzene-1,3,5-tricarboxylic acid). So far, none of the prepared samples formed crystals or contained crystalline domains which would have been suitable for single-crystal or powder-diffraction X-ray analysis. The terminally deprotected dendrimers ( 74 , 75 , and 85 ) are multi-anionic (up to 12 peripheral CO₂H groups) and biodegradable. The macromolecular HB derivatives (molecular weight up to 10150 Da) have been fully characterized by IR, ¹H- and ¹³C-NMR, [α]_D, and elemental analysis. Especially important is the analysis by mass spectrometry with the MALDI-TOF technique (Fig. 2), proving that the products are monodisperse; application of a new variation of this MS method (post source decay = PSD or fragment analysis by structural time of flight = FAST^TM) allows for the observation of metastable fragment ions and, thus, is a tool for structural oligomer analysis (Fig. 3).