Synthesis of 1,1'- and 2,2'-Bicarbazole Alkaloids by Iron(III)-Catalyzed Oxidative Coupling of 2- and 1-Hydroxycarbazoles.

We describe the synthesis of 1,1'- and 2,2'-bicarbazoles by oxidative homocoupling of 2- and 1-hydroxycarbazoles. The oxidative coupling using catalytic amounts of F16 PcFe can be applied to both groups of substrates. Although F16 PcFe generally provides the best yields for the synthesis of 1,1'-bicarbazoles, di-tert-butyl peroxide affords better results for the 2,2'-bicarbazoles. In our study, we have achieved the first syntheses of the biscarbalexines A-C, bisglybomine B, 2,2'-dihydroxy-7,7'-dimethoxy-3,3'-dimethyl-1,1'-bicarbazole, bispyrayafoline C, and bisisomahanine. The iron-catalyzed coupling of koenigine led to an improved synthesis of 8,8''-biskoenigine and afforded an unprecedented decacylic product. Oxidative coupling of 1-hydroxycarbazoles led to bisclausenol, and to the first total syntheses of bismurrayafoline B and D.

Anti-tuberculosis activity and structure-activity relationships of oxygenated tricyclic carbazole alkaloids and synthetic derivatives.

A series of 49 oxygenated tricyclic carbazole derivatives has been tested for inhibition of the growth of Mycobacterium tuberculosis and a mammalian cell line (vero cells). From this series, twelve carbazoles showed a significant anti-TB activity. The four most active compounds were the naturally occurring carbazole alkaloids clauszoline-M (45), murrayaline-C (41), carbalexin-C (27), and the synthetic carbazole derivative 22 with MIC90 values ranging from 1.5 to 3.7µM. The active compounds were virtually nontoxic for the mammalian cell line in the concentration range up to 50µM.

Synthesis of Glycoborine, Glybomine A and B, the Phytoalexin Carbalexin A and the ß-Adrenoreceptor Antagonists Carazolol and Carvedilol.

We describe a regioselective synthesis of 4- or 5-substituted carbazoles by oxidative cyclisation of meta-oxygen-substituted N-phenylanilines. Using the regiodirecting effect of a pivaloyloxy group, we prepared 4-hydroxycarbazole, a precursor for the enantiospecific synthesis of the ß-adrenoreceptor antagonists (-)-(S)-carazolol (5) and (-)-(S)-carvedilol (6). Regioselective palladium(II)-catalysed cyclisation of different diarylamines led to total synthesis of glycoborine (7) and the first total syntheses of the phytoalexin carbalexin A (8), glybomine A (9) and glybomine B (10). For glybomine B (10), a 5-hydroxycarbazole was converted into the corresponding triflate and utilized for introduction of a prenyl substituent.

Novel Expandable Epoxy Beads and Epoxy Particle Foam.

Expanded polymeric beads offer the advantage of being able to produce parts with complex geometries through a consolidation process. However, established polymeric beads are made of thermoplastics, deform and melt beyond their temperature services. In this manuscript, a new technique is proposed to fabricate expandable epoxy beads (EEBs), then expand and fuse them to produce epoxy particle foams (EPFs). This technique is called solid-state carbamate foaming technique. For production of EEBs, a mixture of epoxy, carbamate and hardener is prepared and poured into a 10 mL syringe. The mixture is manually extruded into 60 °C water to obtain a cylindric shape. The extrudate is then further cured to obtain an epoxy oligomer behaving rheological tan delta 3 and 2 at 60 °C. The extrudate is cut into pellets to obtain EEBs. The EEBs are then loaded into an aluminum mold and placed in an oven at 160 °C to expand, fuse to obtain EPFs of 212 kg/m3 and 258 kg/m3. The obtained EPFs provide a Tg of 150-154 °C. The fusion boundaries in EPFs are well formed. Thus, the produced EPFs exhibit a compressive modulus of 50-70 MPa, with a torsion storage modulus at 30 °C of 34-56 MPa.

Investigation of the Thermal and Hydrolytic Degradation of Polylactide during Autoclave Foaming.

Polylactide (PLA) is one of the most important bioplastics worldwide and thus represents a good potential substitute for bead foams made of the fossil-based Polystyrene (PS). However, foaming of PLA comes with a few challenges. One disadvantage of commercially available PLA is its low melt strength and elongation properties, which play an important role in foaming. As a polyester, PLA is also very sensitive to thermal and hydrolytic degradation. Possibilities to overcome these disadvantages can be found in literature, but improving the properties for foaming of PLA as well as the degradation behavior during foaming have not been investigated yet. In this study, reactive extrusion on a twin-screw extruder is used to modify PLA in order to increase the melt strength and to protect it against thermal degradation and hydrolysis. PLA foams are produced in an already known process from the literature and the influence of the modifiers on the properties is estimated. The results show that it is possible to enhance the foaming properties of PLA and to protect it against hydrolysis at the same time.

Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA).

In this comprehensive study, the influence of (i) material specific properties (e.g., molecular weight, zero shear viscosity, D-content) and (ii) process parameters (e.g., saturation temperature, -time, -pressure, and pressure drop rate) on the expansion behavior during the autoclave foaming process were investigated on linear Polylactide (PLA) grades, to identify and evaluate the foam relevant parameters. Its poor rheological behavior is often stated as a drawback of PLA, that limits its foamability. Therefore, nine PLA grades with different melt strength and zero shear viscosity were systematically chosen to identify whether these are the main factors governing the foam expansion and whether there is a critical value for these rheological parameters to be exceeded, to achieve low density foams with fine cells. With pressure drop induced batch foaming experiments, it could be shown that all of the investigated PLA grades could be foamed without the often used chemical modifications, although with different degrees of expansion. Interestingly, PLAs foaming behavior is rather complex and can be influenced by many other factors due to its special nature. A low molecular weight combined with a high ability to crystallize only lead to intermediate density reduction. In contrast, a higher molecular weight (i.e., increased zero shear viscosity) leads to significant increased expandability independent from the D-content. However, the D-content plays a crucial role in terms of foaming temperature and crystallization. Furthermore, the applied process parameters govern foam expansion, cell size and crystallization.