Enantioselective Spirocyclizations from Tryptophanol-Derived Oxazolopiperidone Lactams

An approach to functionalized carbazoles from Z-enoate propargylic alcohols. A unified total synthesis of N-Me-carazostatin, N-Me-carbazoquinocin C and N-Me-lipocarbazole A4

Development of an acid catalyzed, intramolecular benzannulation of indoles for the synthesis of functionalized carbazoles has been reported. The indole appended Z-enoate propargylic alcohols have been employed. The N-EDG-indoles involve the 5-exo-dig cyclization followed by 1,2-migration to give the carbazole-butenoates, whereas the N-EWG-indoles undergo the Z-enoate assisted Meyer-Schuster rearrangement to give the dihydrocarbazole-4-oxo-butanoates. Utilizing one of the 2-methyl-carbazole-butyraldehyde (obtained from the corresponding carbazole-butanoate) as the key intermediate, we have developed a simple approach for an efficient synthesis of N-Me-carazostatin, N-Me-carbazoquinocin C and N-Me-lipocarbazole A4.

Natural Product Inspired Novel Indole based Chiral Scaffold Kills Human Malaria Parasites via Ionic Imbalance Mediated Cell Death

Natural products offer an abundant source of diverse novel scaffolds that inspires development of next generation anti-malarials. With this vision, a library of scaffolds inspired by natural biologically active alkaloids was synthesized from chiral bicyclic lactams with steps/scaffold ratio of 1.7:1. On evaluation of library of scaffolds for their growth inhibitory effect against malaria parasite we found one scaffold with IC50 in low micro molar range. It inhibited parasite growth via disruption of Na+ homeostasis. P-type ATPase, PfATP4 is responsible for maintaining parasite Na+ homeostasis and is a good target for anti-malarials. Molecular docking with our scaffold showed that it fits well in the binding pocket of PfATP4. Moreover, inhibition of Na+-dependent ATPase activity by our potent scaffold suggests that it targets parasite by inhibiting PfATP4, leading to ionic imbalance. However how ionic imbalance attributes to parasite's death is unclear. We show that ionic imbalance caused by scaffold 7 induces autophagy that leads to onset of apoptosis in the parasite evident by the loss of mitochondrial membrane potential (ΔΨm) and DNA degradation. Our study provides a novel strategy for drug discovery and an insight into the molecular mechanism of ionic imbalance mediated death in malaria parasite.

Enantioselective Synthesis of Spiro[indolizidine-1,3'-oxindoles]

A three-step procedure for the enantioselective synthesis of spiro[indolizidine-1,3'-oxindoles], consisting of a stereoselective cyclocondensation reaction between (S)-tryptophanol and a prochiral or racemic δ-oxoester, bromination of the resulting oxazolopiperidone lactam, and a final stereoselective spirocyclization, is reported.

Enantiopure Indolo[2,3-a]quinolizidines: Synthesis and Evaluation as NMDA Receptor Antagonists

Enantiopure tryptophanol is easily obtained from the reduction of its parent natural amino acid trypthophan (available from the chiral pool), and can be used as chiral auxiliary/inductor to control the stereochemical course of a diastereoselective reaction. Furthermore, enantiopure tryptophanol is useful for the syntheses of natural products or biological active molecules containing the aminoalcohol functionality. In this communication, we report the development of a small library of indolo[2,3-a]quinolizidines and evaluation of their activity as N-Methyl d-Aspartate (NMDA) receptor antagonists. The indolo[2,3-a]quinolizidine scaffold was obtained using the following key steps: (i) a stereoselective cyclocondensation of (S)- or (R)-tryptophanol with appropriate racemic δ-oxoesters; (ii) a stereocontrolled cyclization on the indole nucleus. The synthesized enantiopure indolo[2,3-a]quinolizidines were evaluated as NMDA receptor antagonists and one compound was identified to be 2.9-fold more potent as NMDA receptor blocker than amantadine (used in the clinic for Parkinson’s disease). This compound represents a hit compound for the development of novel NMDA receptor antagonists with potential applications in neurodegenerative disorders associated with overactivation of NMDA receptors.

A tryptophanol-derived oxazolopiperidone lactam is cytotoxic against tumors via inhibition of p53 interaction with murine double minute proteins

Inactivation of the p53 tumor suppressor protein by interaction with murine double minute (MDM) proteins, MDM2 and MDMX, is a common event in human tumors expressing wild-type p53. In these tumors, the simultaneous inhibition of these interactions with MDMs, for a full p53 reactivation, represents a promising anticancer strategy. Herein, we report the identification of a dual inhibitor of the p53 interaction with MDM2 and MDMX, the (S)-tryptophanol derivative OXAZ-1, from the screening of a small library of enantiopure tryptophanol-derived oxazolopiperidone lactams, using a yeast-based assay. With human colon adenocarcinoma HCT116 cell lines expressing wild-type p53 (HCT116 p53(+/+)) and its p53-null isogenic derivative (HCT116 p53(-/-)), it was shown that OXAZ-1 induced a p53-dependent tumor growth-inhibitory effect. In fact, OXAZ-1 induced p53 stabilization, up-regulated p53 transcription targets, such as MDM2, MDMX, p21, Puma and Bax, and led to PARP cleavage, in p53(+/+), but not in p53(-/-), HCT116 cells. In addition, similar tumor cytotoxic effects were observed for OXAZ-1 against MDMX-overexpressing breast adenocarcinoma MCF-7 tumor cells, commonly described as highly resistant to MDM2-only inhibitors. In HCT116 p53(+/+) cells, the disruption of the p53 interaction with MDMs by OXAZ-1 was further confirmed by co-immunoprecipitation. It was also shown that OXAZ-1 potently triggered a p53-dependent mitochondria-mediated apoptosis, characterized by reactive oxygen species generation, mitochondrial membrane potential dissipation, Bax translocation to mitochondria, and cytochrome c release, and exhibited a p53-dependent synergistic effect with conventional chemotherapeutic drugs. Collectively, in this work, a novel selective activator of the p53 pathway is reported with promising antitumor properties to be explored either alone or combined with conventional chemotherapeutic drugs. Moreover, OXAZ-1 may represent a promising starting scaffold to search for new dual inhibitors of the p53-MDMs interaction.

Metal-free [3 + 2 + 1]/[2 + 2 + 1] biscyclization: stereospecific construction with concomitant functionalization of indolizin-5(1H)-one

A metal-free [3 + 2 + 1]/[2 + 2 + 1] biscyclization strategy has been developed for the stereospecific construction with concomitant derivation of biologically significant indolizin-5(1H)-ones from simple and commercial starting materials. The transformations are notable because they can yield five new σ bonds and six stereocenters including a quaternary carbon center in a single operation.

Synthesis of spirocyclic indolines by interruption of the Bischler-Napieralski reaction

The development of a versatile method for the synthesis of spirocyclic pyrrolidinoindolines is discussed. Treatment of N-acyltryptamines with trifluoromethanesulfonic anhydride-2-chloropyridine reagent combination affords highly persistent spiroindoleninium ions that are subject to intra- and intermolecular addition at C2 by nucleophiles.

Enantioselective formal synthesis of ent-rhynchophylline and ent-isorhynchophylline

Starting from (S)-tryptophanol, a formal synthesis of ent-rhynchophylline and ent-isorhynchophylline, involving stereoselective cyclocondensation, spirocyclization, and alkylation reactions, and the final adjustment of the oxidation level at the oxindole and piperidine moieties, is reported.