Isocyanide-Based Multicomponent Reactions Coupled One-Pot Process: Efficient Tools to Diversity-Oriented Synthesis of Structural Peptidomimetics.

Multicomponent diversity-oriented synthesis (DOS) of conformationally anchored structural peptidomimetics like 2,5-diketopiperazines (2,5-DKP) containing heterocyclic bioisosteres of the amide bond, such as 1,2,3-triazoles and 1,5-disubstituted tetrazoles (1,5-DS-T) is described. Structural peptidomimetics are synthesized from similar available starting materials, via a strategy based on isocyanide-based multicomponent reactions (IMCRs): Ugi-4CR and Ugi-Azide (UA), followed by a one-pot process: SN 2/intramolecular alkyne-azide cycloaddition (IAAC). The sequential aligning of two powerful synthetic tools (IMCR and IAAC) has parallelly contributed to generate anchored conformation and complexity in target molecules, which are considered structural peptidomimetics of 2,5-DKP. Herein, the 1,2,3-triazole ring plays a key role in the preference for the boat conformation. Furthermore, the use of UA reaction generates scaffold diversity at the N-1 α-carbon of the pyrazinone ring, replacing a linear amide bond with a heterocyclic bioisostere such as 1,5-DS-T leading to the synthesis of novel tricyclic peptidomimetics. The DFT calculations confirmed the boat conformation of the synthesized molecules.

TiCl4 catalyzed cleavage of (25R)-22-oxo-23-spiroketals. Synthesis of sapogenins with furostanol and pyranone E rings on the side chain.

The regioselective opening of the F ring of 22-oxo-23-spiroketals 7a-d using TiCl4 in acetic anhydride yielded the novel furostanols 11a-d along with cholestanic derivatives 8a-d with pyranone E ring. The structures of the new derivatives thus obtained were established using one- (DEPT) and two-dimensional 1H, 13C NMR experiments (COSY, HSQC, HMBC, NOESY). The 22α-hydroxyl orientation in compounds 11a-d was proposed by comparison of the 13C chemical shifts with those of other aglycone members of this family, and confirmed by combined NOESY and X-ray diffraction analysis of compound 11a.

Access to 27-Nortomatidine and 27-Norsoladulcidine Derivatives.

Synthesis of (22 R)- and (22 S)-27-norspirosolane alkaloids from tigogenin, epismilagenin, and smilagenin is described. The alkaloids were prepared from readily available dinorcholanic lactones via their reaction with 4-chlorobutyllithium followed by substitution of chloride with azide and reductive N-cyclization under the Staudinger conditions.