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 CO 2 H groups) and biodegradable. The macromolecular HB derivatives (molecular weight up to 10150 Da) have been fully characterized by IR, 1 H‐ and 13 C‐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 f ragment a nalysis by structural t ime of flight = FAST TM ) allows for the observation of metastable fragment ions and, thus, is a tool for structural oligomer analysis ( Fig. 3 ).