Both diastereomeric right-handed (P) and left-handed (M) 310-helices exist in homopeptides having twelve chiral centers at the side-chain bicyclic skeletons.

The synthesis of a 6-CF3-substituted 2-amino-dihydro-1,3-thiazine via N,N-diethylaminosulfur trifluoride (DAST)-mediated cyclization of N-hydroxypropyl thiourea 6 is described. This reaction gave 6-CF3-1,3-thiazine 7 with high chemical yield and chemoselectivity, suppressing the common byproduct of oxazine 8. This new protocol enabled access to 6-CF3-substituted 1,3-thiazine β-secretase inhibitor 2.

Chiral bicyclic α‐amino acid (R,R)‐Ab5,6=c with stereogenic centers at the γ‐position of fused‐ring junctions, and its enantiomer (S,S)‐Ab5,6=c, were synthesized. The CD spectra of (R,R)‐Ab5,6=c oligomers indicated that the (R,R)‐Ab5,6=c hexapeptide formed a mixture of right‐handed (P)‐ and left‐handed (M)‐310‐helices, while, in the (R,R)‐Ab5,6=c nonapeptide, a right‐handed (P)‐310‐helix slightly dominated over the (M)‐helix. X‐Ray crystallographic analyses of (S,S)‐tripeptide and (R,R)‐hexapeptide revealed that both the tripeptide and hexapeptide formed a mixture of (P)‐ and (M)‐310‐helices, respectively. These results indicated that the side‐chain environments around the stereogenic centers are particularly important to control the helical‐screw handedness of foldamers.

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