A new class of positional isomeric pairs of -Boc protected oligopeptides comprised of alternating nucleoside derived β-amino acid (β-Nda-) and L-amino acid residues (alanine, valine, and phenylalanine) have been differentiated by both positive and negative ion electrospray ionization ion-trap tandem mass spectrometry (ESI-MS n ). The protonated dipeptide positional isomers with β-Nda-at the N-terminus lose CH 3 OH, NH 3 , and C 2 H 4 O 2 , whereas these processes are absent for the peptides with L-amino acids at the N-terminus. Instead, the presence of L-amino acids at the N-terminus results in characteristic retro-Mannich reaction involving elimination of imine. A good correlation has been observed between the conformational structure of the peptides and the abundance of y n + and b n + ions in MS n spectra. In the case of tetrapeptide isomers that are reported to form helical structures in solution phase, no y n + and b n + ions are observed when the corresponding amide -NH-participates in the helical structures. In contrast, significant y n + and b n + ions are formed when the amide -NH-is not involved in the H-bonding. In the case of tetra-and hexapeptides, it is observed that abundant b n + ions are formed, presumably with stable oxazolone structures when the C-terminus of the b n + ions possessed L-amino acid and the β-Nda-at the C-terminus appears to prevent the cyclization process leading to the absence of corresponding b n + ions.
A para‐toluenesulfonic acid (pTSA) catalyzed domino aza‐Piancatelli rearrangement/Michael reaction was developed for the construction of 1,4‐benzodiazepin‐5‐ones in one pot. The method proceeds well in the presence of various furfurylcarbinols and o‐aminobenzamides to give products that contain medicinally relevant chemical entities.
A concise preparation of triazole-linked deoxynucleoside phosphoramidite for its direct use in solid-phase oligonucleotide synthesis is reported. This dimer has successfully been utilized in solid-phase synthesis to make the 10-and 12-mer oligomers.
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