Mass spectrometric-based investigation of differentially protected azatryptophan derivatives using Orbitrap mass spectrometry: Differentiation of positional isomers under protonation and alkali-cationization conditions.

RATIONALE: Differentiation and structural characterization of positional isomers of differentially protected azatryptophan derivatives using electrospray ionization high-resolution tandem mass spectrometry (ESI-HRMS/MS) is important from the perspective of drug discovery research. Also, these derivatives can be used as building blocks for the synthesis of various biologically active compounds and have attracted significant attention in the field of modern drug discovery, especially peptide-based drugs, protein folding and protein-protein interactions because of their interesting spectral properties. METHODS: ESI-HRMS/MS in positive ionization mode was used to differentiate and characterize positional isomers of protected azatryptophan derivatives. RESULTS: ESI-HRMS/MS of [M + H]+ and [M + Na]+ ions of positional isomers of differentially protected azatryptophan derivatives display distinct fragmentation patterns. The MS/MS of [M + H]+ ion of isomer 1 showed an additional ion at m/z 358.0846 ([M + H-Boc-C14 H10 -HF]+ ) which was not present for 4. The fragment ion at m/z 332.0857 was observed for 1 and not for 4 which would be formed by the expulsion of butyloxycarbonyl (Boc) and fluorenylmethyloxycarbonyl (Fmoc) groups. Moreover, the ions 422.0812 and 378.0912 are found to be relatively more abundant for isomer 4 which could be probably attributed to the formation of stable ions. Similarly, other positional isomers exhibited distinct fragmentation from one another. CONCLUSIONS: The present study demonstrates that ESI-HRMS/MS can be used for differentiation and structural characterization of positional isomers of protected azatryptophan derivatives. The MS/MS of [M + H]+ and [M + Na]+ ions of these positional isomers displayed differences in their fragmentation behaviour. The impact of different substitutions at different positions (1 and 6) of protected azatryptophan derivatives (1-6) on their fragmentation behaviour was also investigated in detail. Also, the nitrogen atom at different positions in the pyrrolopyridine ring led to different fragmentation patterns.

Synthesis of Differentially Protected Azatryptophan Analogs via Pd2(dba)3/XPhos Catalyzed Negishi Coupling of N-Ts Azaindole Halides with Zinc Derivative from Fmoc-Protected tert-Butyl (R)-2-Amino-3-iodopropanoate.

Unnatural amino acids play an important role in peptide based drug discovery. Herein, we report a class of differentially protected azatryptophan derivatives synthesized from N-tosyl-3-haloazaindoles 1 and Fmoc-protected tert-butyl iodoalanine 2 via a Negishi coupling. Through ligand screening, Pd2(dba)3/XPhos was found to be a superior catalyst for the coupling of 1 with the zinc derivative of 2 to give tert-butyl (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-3-(1-tosyl-1H-pyrrolo[2,3-b]pyridin-3-yl)propanoate derivatives 3 in 69-91% isolated yields. In addition, we have demonstrated that the protecting groups, namely, Ts, Fmoc, and tBu, can be easily removed selectively.

Design, synthesis and biological evaluation of phenol-linked uncialamycin antibody-drug conjugates.

Uncialamycin is one of the structurally simpler and newer members of enediyne family of natural products. It exhibits highly potent activity against several types of bacteria and cancer cells. Described herein is a strategy for the targeted delivery of this cytotoxic agent to tumors using an antibody-drug conjugate (ADC) approach. Central to the design of ADC were the generation of potent and chemically stable uncialamycin analogues and attachment of protease cleavable linkers to newly realized phenolic handles to prepare linker-payloads. Conjugation of the linker-payloads to tumor targeting antibody, in vitro activity and in vivo evaluation are presented.

Discovery of a Highly Selective JAK2 Inhibitor, BMS-911543, for the Treatment of Myeloproliferative Neoplasms.

JAK2 kinase inhibitors are a promising new class of agents for the treatment of myeloproliferative neoplasms and have potential for the treatment of other diseases possessing a deregulated JAK2-STAT pathway. X-ray structure and ADME guided refinement of C-4 heterocycles to address metabolic liability present in dialkylthiazole 1 led to the discovery of a clinical candidate, BMS-911543 (11), with excellent kinome selectivity, in vivo PD activity, and safety profile.