A unified approach to access Nβ-protected amino alkyl isothiocyanates using Nβ-protected amino alkyl azides through a general strategy of Staudinger/aza-Wittig reaction is described. The type of protocol used to access isothiocyanates depends on the availability of precursors and also, especially in the amino acid chemistry, on the behavior of other labile groups towards the reagents used in the protocols; fortunately, we were not concerned about both these factors as precursor-azides were prepared easily by standard protocols, and the present protocol can pave the way for accessing title compounds without affecting Boc, Cbz and Fmoc protecting groups, and benzyl and tertiary butyl groups in the side chains. The present strategy eliminates the need for the use of amines to obtain title compounds and thus, this method is step-economical; additional advantages include retention of chirality, convenient handling and easy purification. A few hitherto unreported compounds were also prepared, and all final compounds were completely characterized by IR, mass, optical rotation, and 1H and 13C NMR studies.
The Ugi‐azide reaction of an enantiopure amino acid derived isocyanides, amino acid esters, aldehydes and TMS‐N3 in MeOH:THF solvent system at 50 °C yielded peptidomimetics comprising tetrazole as amide bond isostere. Both N‐terminal (α‐isocyanoesters) and C‐terminal isocyanides (Nβ‐Cbz‐protected amino alkyl isocyanides) have been employed to yield diversified tetrazole peptidomimetics, having the possibility of further derivatization through either N‐ or C‐terminal chain elongation. Ugi‐azide reaction is a isocyanide based multi‐component reaction (IMCR), as a result, change in amino acid derived isocyanides had given structurally diverse products of biological interest. Good yields of products were obtained after column purification and were stable for shelf storage. The products are novel and were well characterized by Mass, 1H NMR and 13C NMR spectral studies. The present method offers several advantages such as one‐pot simple procedure, high yields and easy purification of products.
Mild and highly efficient I2 and Et3N aided cyclodeselenization of in situ generated selenosemicarbazide is described to obtain 2-amino-1,3,4-oxadiazole peptidomimetics.
The synthesis of α‐ureidopeptidomimetics employing a simple, mild and straight forward route starting from benzyloxy carbonyl (Cbz‐) protected amino acid esters in presence of 2‐Cl pyridine (2‐chloropyridine) and Tf2O (triflic anhydride) in one‐pot is described. The in situ generated isocyanate intermediates react with amino acid esters to yield the title compounds in good yields (89‐96%) and the protocol proved to be racemization free.
An efficient one‐pot synthesis of 2‐iminohydantoins and 2‐amino‐1H‐imidazol‐4(5H)‐ones via iodine mediated intramolecular cyclodeselenization of intermediate selenourea tethered amides/peptides is described. The method employs selenophilic ability of environmentally benign iodine to effect the deselenization at room temperature, thereby avoids harsh conditions that are generally employed in the synthesis of iminohydantoins. Significantly 2‐(N‐alkylamino)‐1H‐imidazol‐4(5H)‐ones and 2‐iminohydantoin conjugates of di‐ and tripeptides could be synthesized. Other advantages of the method include mild condition, short duration, wide substrate scope, simple workup and purification of the products.
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