The C-linked carbo-beta-peptides, oligomers of a new class of C-linked carbo-beta3-amino acids, have been shown to generate mixed 12/10 and 10/12 helices. The design involves use of "alternating chirality" of the epimeric (at the amine center) monomers to control the stability of these helices. The observation of stable 12/10 helix in a tripeptide and 10/12 helix in a tetrapeptide is unprecedented.

Dedicated to Professor Goverdhan Mehta on the occasion of his 60th birthdayGlycals are ambident electrophiles capable of reacting with various nucleophiles such as alcohols, malonates, and silyl nucleophiles under the influence of acid catalysts or oxidants to produce 2,3-unsaturated glycosides. [1,2] In recent times, indium halides have emerged as versatile Lewis acid catalysts imparting high regio-, chemo-, and diastereoselectivity to a variety of organic transformations.[3] Compared to conventional Lewis acids, indium tribromide, in particular, has advantages of low catalyst loading, moisture stability, and catalyst recycling.[4] C-Glycosides bearing carbon-linked heterocycles have attracted great attention owing to their potent antiviral and antitumor behavior.[5] Because of these properties of aryl glycosides, we have attempted C-glycosidation with aryl amines to synthesize aryl C-glycosides with a free amino functionality for further derivatization. Interestingly, we observed for the first time an unusual formation of benzofused heterobicycles in the aminoglycosidation.In our continuing research on glycoside synthesis, [6] we have made unprecedented observations in the aminoglycosidation reactions of glycals with aryl amines, which we report here. Initially, we attempted the aminoglycosidation reaction of d-glucal with aniline using 10 mol % indium(iii) bromide as a novel glycosyl activator. Interestingly, the unusual bicyclic adduct 3 a (R = H) was isolated in 85 % yield with high stereoselectivity (Scheme 1).The product 3 a was characterized thoroughly by various NMR experiments including double-quantum-filtered correlation spectroscopy (DQFCOSY), nuclear Overhauser effect spectroscopy (NOESY), heteronuclear single-quantum correlation spectroscopy (HSQC), [7] and 3 J CH -optimized HMBC experiments.[8] The edited HSQC spectrum showed the presence of two methylene groups in addition to eight methine and two methyl groups. The location of the methylene group in the bridge of a bicyclononene-like structure was confirmed by the presence of small couplings between these protons and the bridgehead protons H1 and H3 (J H1-H2(pro-S) = 3.7 Hz, J H1-H2(pro-R) = 1.8 Hz, J H2(pro-S)-H3 = 2.4 Hz, and J H2(pro-R)-H3 = 4.6 Hz; Figure 1)). Fusion of the bicyclononene and the aromatic ring at C1ÀC11 and NHÀC3 was confirmed by nOe interactions between H1 and H12. Further support for the structure came from HMBC peaks for H1/C12, H1/C11, H1/C16 and H12/C1. The two six-membered rings of the bicyclononane moiety have two different conformations. The one containing oxygen takes a chair form,

alpha/beta-Hybrid peptides are prepared from amino acids with proteinogenic side chains on the basis of the concept of "alternating chirality", involving D-Phe and a beta3-hVal. Through the extensive NMR, CD, and MD studies, robust left-handed 11/9-mixed helices were identified in these peptides in CDCl3 solutions, wherein the 11/9-mixed helix was observed even in a small peptide with three residues.

A highly regio- and stereoselective route for the synthesis of racemic and nonracemic tetrahydroquinoxalines via the S(N)2-type ring-opening of activated aziridines with 2-bromoanilines followed by the Pd-catalyzed intramolecular C-N bond formation is described.

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