Total synthesis of (+/-)-jamtine using a thionium/N-acyliminium ion cascade

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.

Asymmetric total synthesis of the proposed structure of the medicinal alkaloid jamtine using the chiral base approach

[reaction: see text] A highly step-economic asymmetric synthesis of the tetracyclic structure assigned to the medicinal alkaloid jamtine has been accomplished using a chiral lithium amide base desymmetrization of a ring-fused imide. The structure synthesized appears to be different from that of the natural product originally reported.

A short diastereoselective synthesis of the putative alkaloid jamtine, using a tandem pummerer/mannich cyclization sequence

Treatment of 2-phenylhex-5-enal with benzylamine followed by sequential reaction with ethylthioacetyl chloride and sodium periodate oxidation afforded a E/Z mixture of alpha-sulfinylamides. As anticipated from a 4pi-conrotatory mechanism, cyclization of each olefin afforded fused isoquinoline lactams as single diastereomers epimeric at the ethylthio position without any cross contamination. Some preliminary studies were directed toward the synthesis of mesembrine using a 3,4-dimethoxy aryl group. In this case, the Z-enamide prefers to undergo electrophilic aromatic substitution to give a substituted azepinone as the preferred product in 87% yield. In contrast, the E-enamide isomer provided the desired hydroindolone. The convergency and stereochemical control associated with the tandem Pummerer /Mannich cyclization make it particularly suited for the assembly of jamtine, a tetrahydroisoquinoline alkaloid reputed for its therapeutic properties. The key step in the synthesis involves a domino thionium/N-acyliminium ion cyclization to provide the tricyclic ring skeleton 27a as the major diastereomer. Deprotonation of 27a with NaH gave 28a, which contains the fully assembled skeleton of jamtine. Completion of the synthesis entailed installation of the double bond and reduction of the lactam. Oxidation of a synthetic sample of jamtine with MCPBA afforded the corresponding N-oxide, which does not match the spectral data reported in the literature for this alkaloid. Our synthetic efforts raise the possibility of a revision of the earlier assignment.