Total Synthesis of Peganumine A: Journey towards drug discovery, organocatalyst design and synthetic methodology development

The primary aim of this thesis was to develop an efficient synthetic route of peganumin A and its application to the discovery of potent analogues. Peganumine A was isolated from the seeds of Peganum harmala in 2014, and is distinguished from the classic tetrahydro-β-carboline alkaloids due to the unique 5,5-dimethyl-2,7-diazabicyclo[2.2.1]heptan-3-one ring system, as well as the excellent cytotoxicity. In the initial total synthesis of racemic peganumine A, three different strategies were investigated. One strategy could realize the total synthesis of peganumine A in a protection group free fashion, which relied on a Bischler–Napieralski type annulation and a Pictet– Spengler reaction cascade to construct the two tetrahydro-β-carboline cores. With the powerful synthetic route in hand, 11 analogues were designed and synthesized based on the functionoriented strategy. By further cytotoxic assay, not only the preliminary SAR was illustrated, but also a potent analogue was discovered. Based on the racemic synthetic route, organocatalysis was applied to the asymmetric syntheses of peganumine A and its analogues. The enantioselective synthesis of was realized by a chiral disulfonimide catalyzed Pictet–Spengler reaction cascade. However, the highly enantioenriched analogues could not be obtained by the chiral disulfonimide catalyzed Pictet–Spengler reaction cascade. Through design, synthesis and screening of chiral N-phosphinyl phosphoramides, a highly enantioselective synthesis of the potent analogue was achieved. Besides the original three strategies, two new N-acyliminium ion cyclization strategies were further explored to improve the efficiency of the synthetic route. Another 5-step synthesis of peganumine A was realized and featured a Pictet‒Spengler reaction–iminium ion cyclization–aminalation cascade to assemble the two tetrahydro-β-carboline motifs in a one-step synthesis. In the protection group free total synthesis of peganumine A, an annulation reaction was discovered, which was then developed into a general methodology to construct the polycyclic fused quinolizidine scaffolds. This new approach was then applied to the total synthesis of harmalanine, harmalacinine, nortetoyobyrine and ilicifoline B, and the formal total synthesis of deplancheine, 10-desbromoarborescidine A, hirsutine, rhynchophylline and isorhynchophylline. In summary, this thesis focused on the development of efficient synthetic routes towards peganumine A, which promoted the discovery of a potent analogue, design of new organocatalyst and investigation of new synthetic methodology.Das primäre Ziel dieser Dissertation war die Entwicklung einer effizienten Route zur Synthese von Peganumin A und die Anwendung dieser Route zur Entdeckung potenter Analoga. Peganumin A wurde aus den Samen der Steppenraute Peganum harmala in 2014 isoliert und unterscheidet sich von den klassischen Tetrahydro-β-carbolin-Alkaloiden durch das einzigartige 5,5-Dimethyl-2,7-diazabicyclo[2.2.1]heptan-3-on-Ringsystem, sowie eine hohe Zytotoxizität. Bei der anfänglichen Totalsynthese von racemischem Peganumin A wurden drei verschiedene Strategien untersucht. Eine dieser Strategien lieferte schließlich den Naturstoff in einer schutzgruppenfreien Synthese. Dabei wurde das Tetrahydro-β-carbolin-Gerüst durch eine Bischler-Napieralski-artige Anellierung und einer Pictet-Spengler-Reaktionskaskade aufgebaut. Mit Hilfe dieser Syntheseroute wurden 11 weitere Analoga, basierend auf dieser funktionsorientierten Strategie, entworfen und synthetisiert. Durch zytotoxische Tests konnte nicht nur eine vorläufige SAR ermittelt, sondern ein potentes Analogon entdeckt werden. Die Verwendung von Organokatalyse erlaubte, basierend auf der Strategie für die Synthese des Racemats, eine asymmetrische Synthese von Peganumin A und dessen Analoga. Während die hohe Enantioselektivität für Peganumin A durch ein chirales Disulfonimid als Katalysator für die Pictet-Spengler-Reaktionskaskade erreicht werden konnte, war dieses für die entsprechenden Analoga nicht möglich. Durch Design, Synthese und Screening chiraler N-Phospinylphosphoramide gelang es schließlich einen geeigneten Katalysator für die hoch enantioselektive Synthese eines potenten Analogons zu finden. Neben den ursprünglichen drei Strategien wurden zusätzlich zwei neue Strategien zur Zyklisierung von N-Acyliminiumionen untersucht, um die Effizienz der Syntheseroute zu verbessern. Dabei konnte eine fünfstufige Synthese von Peganumin A durch eine Kaskade, bestehend aus Pictet-Spengler-Reaktion, Iminiumionenzyklisierung und Aminalbildung, die es ermöglichte die Tetrahydro-β-carbolin-Motive in einer Stufe aufzubauen, realisiert werden. Die Anellierungsreaktion aus der Synthese von Peganumin A wurde anschließend zu einer allgemeinen Methodik für den Aufbau von polyzyklischen, fusionierten Chinolizidingerüsten weiterentwickelt. Dieser neue Ansatz wurde schließlich auf die Totalsynthese von Harmalanin, Harmalacinin, Nortetoyobyrin und Ilicifolin B, sowie die Formalsynthese von Deplanchein, 10-Desbromarborescidin A, Hirsutin, Rhynchophyllin und Isorhynchophyllin angewandt. Zusammenfassend konnten mit dieser Arbeit effizienter Syntheserouten von Peganumin A realisieren werden, wodurch sich die Entdeckung eines potenten Analogons sowie das Design eines neuen Organokatalysators und Untersuchungen neuer Synthesemethoden ergaben

Unified Synthesis of Polycyclic Alkaloids by Complementary Carbonyl Activation

A complementary dual carbonyl activation strategy for the synthesis of polycyclic alkaloids has been developed. Successful applications include the synthesis of tetracyclic alkaloids harmalanine and harmalacinine, pentacyclic indoloquinolizidine alkaloid nortetoyobyrine, and octacyclic β-carboline alkaloid peganumine A. The latter synthesis features a protecting-group-free assembly and an asymmetric disulfonimide-catalyzed cyclization. Furthermore, formal syntheses of hirsutine, deplancheine, 10-desbromoarborescidine A, and oxindole alkaloids rhynchophylline and isorhynchophylline have been achieved. Finally, a concise synthesis of berberine alkaloid ilicifoline B was completed

Detecting top-Higgs at high energy e+e−e^{+}e^{-} colliders

We calculate the contributions of the top-Higgs $h_{t}^{0}$ predicted by topcolor assisted technicolor(TC2) models to $e^{+}e^{-}\longrightarrow \overline{t}c\overline{\nu}_{e}\nu_{e}$ and compare the results with the contributions of $h^{0}_{t}$ to the processes $e^{+}e^{-}\longrightarrow Z h^{0}_{t}\longrightarrow Z\overline{t}c$ and $e^+e^-\longrightarrow \gamma h^{0}_{t} \longrightarrow \gamma \overline{t}c$. We find that $e^{+}e^{-} \longrightarrow\overline{t}c\overline{\nu}_{e}\nu_{e}$ is very sensitive to $h^{0}_{t}$, which can be easy detected via this process at high-energy $e^{+}e^{-}$ collider(LC) experiments with $\sqrt{s}\geq 500$ $GeV$, as long as its mass below the $\overline{t}t$ threshold. The process $e^{+}e^{-} \longrightarrow \gamma\overline{t}c$ also can be used to detect $h^{0}_{t}$ at LC experiments.Comment: latex file, 10 pages, 4 eps figure, submitted to Phys. Lett.

Neutral top-pion and top-charm production in high energy e+e−e^{+}e^{-} collisions

We calculate the contributions of the neutral top-pion, predicted by topcolor-assisted technicolor (TC2) theory, to top-charm production via the processes $\gamma\gamma \longrightarrow\bar{t}c$ and $e^{+}e^{-}\longrightarrow \gamma\gamma\longrightarrow \bar{t}c$ at the high energy linear $e^{+}e^{-}$ collider (LC) experiments. The cross section is of order $10^{-2}pb$ in most of the parameter space of TC2 theory, which may be detected at the LC experiments. So the process $e^{+}e^{-}\longrightarrow \bar{t}c$ can be used to detect the signature of TC2 theory.Comment: Latex file, 8 pages with 4 eps figures. to be published Phys.Lett.

A colorimetric method for point mutation detection using high-fidelity DNA ligase

The present study reported proof-of-principle for a genotyping assay approach that can detect single nucleotide polymorphisms (SNPs) through the gold nanoparticle assembly and the ligase reaction. By incorporating the high-fidelity DNA ligase (Tth DNA ligase) into the allele-specific ligation-based gold nanoparticle assembly, this assay provided a convenient yet powerful colorimetric detection that enabled a straightforward single-base discrimination without the need of precise temperature control. Additionally, the ligase reaction can be performed at a relatively high temperature, which offers the benefit for mitigating the non-specific assembly of gold nanoparticles induced by interfering DNA strands. The assay could be implemented via three steps: a hybridization reaction that allowed two gold nanoparticle-tagged probes to hybrid with the target DNA strand, a ligase reaction that generates the ligation between perfectly matched probes while no ligation occurred between mismatched ones and a thermal treatment at a relatively high temperature that discriminate the ligation of probes. When the reaction mixture was heated to denature the formed duplex, the purple color of the perfect-match solution would not revert to red, while the mismatch gave a red color as the assembled gold nanoparticles disparted. The present approach has been demonstrated with the identification of a single-base mutation in codon 12 of a K-ras oncogene that is of significant value for colorectal cancers diagnosis, and the wild-type and mutant type were successfully scored. To our knowledge, this was the first report concerning SNP detection based on the ligase reaction and the gold nanoparticle assembly. Owing to its ease of operation and high specificity, it was expected that the proposed procedure might hold great promise in practical clinical diagnosis of gene-mutant diseases

The flavor-changing rare top decays t→cVVt\to c V V in topcolor-assisted technicolor theory

In the framework of topcolor-assisted technicolor (TC2) theory, we calculate the contributions of the scalars(the neutral top-pion $\pi_{t}^{0}$ and the top-Higgs $h_{t}^{0}$) to the flavor-changing rare top decays $t\to c V V$(V= W, g, $\gamma$ or Z). Our results show that $h_{t}^{0}$ can enhance the standard model $B_{r}^{SM}(t\longrightarrow cWW)$ by several orders of magnitude for most of the parameter space. The peak of the branching ratio resonance emerges when the top-Higgs mass is between $2m_{W}$ and $m_{t}$. The branching ratio $B_{r}(t\to c W W)$ can reach $10^{-3}$ in the narrow range.Comment: Latex file, 11pages, 2 eps figure

Contrasting off-line segmentation decisions with on-line word segmentation during reading

In two experiments, we investigated the correspondences between off-line word segmentation and on-line segmentation processing during Chinese reading. In Experiment 1, participants were asked to read sentences which contained critical four-character strings, and then they were required to segment the same sentences into words in a later off-line word segmentation task. For each item, participants were split into 1-word segmenters (who segmented four-character strings as a single word) and 2-word segmenters (who segmented four-character strings as 2 two-character words). Thus, we split participants into two groups (1-word segmenters and 2-word segmenters) according to their off-line segmentation bias. The data analysis showed no reliable group effect on all the measures. In order to avoid the heterogeneity of participants and stimuli in Experiment 1, two groups of participants (1-word segmenters and 2-word segmenters) and three types of critical four-character string (1-word strings, ambiguous strings and 2-word strings) were identified in a norming study in Experiment 2. Participants were required to read sentences containing these critical strings. There was no reliable group effect in Experiment 2, as was the case in Experiment 1. However, in Experiment 2, participants spent less time and made fewer fixations on 1-word strings compared to ambiguous and 2-word strings. These results indicate that the off-line word segmentation preferences do not necessarily reflect on-line word segmentation processing during Chinese reading, and that Chinese readers exhibit flexibility such that word, or multiple constituent, segmentation commitments are made on-line