A generic macrocyclic peptide structure 2 was designed as a potential inhibitor of a range of proteinases, by using as a basis for the design the known structures of a series of enzyme-inhibitor complexes. The macrocyclic nature of the target 2 was chosen so as to reduce the entropic advantage in the hydrolytic enzymatic step, and thereby to inhibit the function of the enzyme. The nature of the linking group was identified as a benzoxazole by molecular modeling, so as to preserve the recognized conformation of the peptide chain. The specificity of the potential inhibitor was tuned by variation of the P(1) group (by incorporating phenylalanine, aspartic acid, or lysine), to allow recognition by different enzyme classes. The targets were prepared from the bis-amino acid derivative 5, itself prepared using the Pd-catalyzed coupling of an organozinc reagent with the iodobenzothiazole 7 and subsequent macrocyclization of the open-chain derivatives 22-24 using HATU. None of the macrocylic compounds 25, 28-30, and 32 inhibited their target enzymes. NMR and MS studies on the interaction of macrocycle 29 and chymotrypsin established that compound 29 was in fact a substrate of the enzyme. This result indicated that while the design had been partially successful in identifying a compound that bound, the reduction in entropic advantage due to its macrocyclic nature was not sufficient to allow 29 to act as an inhibitor.

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A new approach to the synthesis of unsaturated nitro-allenyltetrahydrofurans 3 and -tetrahydropyrans 5 has been developed, involving oxa-Michael addition/S N 2Ј substitution of propargyl and homopropargyl alcohol derivatives 2a and 4h on nitroalkenes1a−g. Complete allylic 1,3-strain control dur-

Upon one-electron oxidation by ammonium hexanitratocerate(iv) (CAN), aci-nitro anions 3a-d resulting from oxa-Michael addition of allylic alcohol to a,b-disubstituted nitroalkenes 1a-d undergo stereoselective radical cyclization into 3-nitro-4-nitrooxymethyltetrahydrofurans 6a-d and 3-nitro-4-hydroxymethyltetrahydrofurans 7,8a-d.

The synthesis of various heterocycles and carbocycles (tetrahydrofurans, pyrrolidines, cyclopentanes) has been achieved by using new and efficient ionic addition/cyclization sequences. Nitroolefins play an important role in the Michael addition induced ring-closing reactions (MIRC) reported in the present article, with various substituted alcohols, amines, Grignard reactants, or malonate derivatives acting as the nucleophile partner. The optimized cascade reactions were high yielding in most cases and highly stereoselective, creating up to three stereogenic centers starting from achiral substrates.