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-A 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 = FASTTM) allows for the observation of metastable fragment ions and, thus, is a tool for structural oligomer analysis (Fig. 3).