Synthesis of Tetrahydroxyquinolizidines: Ring-Expanded Analogs of the Mannosidase Inhibitor Swainsonine
摘要:
The indolizidine azasugar swainsonine (1) is an important inhibitor of mannosidase II and has shown antitumor and immunomodulatory activity. A comparison of the structure of swainsonine and D-mannopyranose shows that swainsonine lacks the C(4) hydroxymethine group of mannose. Ring-expanded quinolizidine analogs 4 of swainsonine were prepared where the ''missing'' hydroxymethine group was incorporated into the pyrrolidine ring of swainsonine between C(1) and C(8a). The quinolizidine analogs 4 resemble both D-mannopyranose and the related azasugar deoxymannojirimycin, a selective inhibitor of the glycoprotein processing enzyme mannosidase I. D-Arabinose was converted into the omega-halo azidoalkene 13, which was subjected to thermolysis, a strategy which had been successful in an earlier synthesis of swainsonine itself. Rather than the desired quinolizidine 4, the pyridinium ion 16 was produced. An alternate synthesis of all four C(9)/C(9a) diastereomers of 4 was developed which relied on the reductive double-alkylation of epoxides bearing remote azido and chloro groups. Thus, reduction of compounds 21 alpha, 21 beta, 26, and 27 resulted in the formation of the quinolizidines 22, 23, 28, and 29, which were deprotected to give the quinolizidine analogs of swainsonine (9S,9aR)-4, (9R,9aS)-4, (9S,9aS)-4, and (9R,9aR)-4, respectively. An alternate synthesis of(9R,9aR)-4 involving the reductive N-alkylation of a cyclic imine was also developed. None of the quinolizidines showed significant glycosidase activity in screens against mannosidases, glucosidases, or fucosidases. Speculation on the significance of these findings is presented.
A direct approach to the synthesis of indolizidine and quinolizidine scaffolds of iminosugars is described. The presented strategy is based on a one-pot sugar lactam reduction with Schwartz’s reagent followed by a diastereoselective Mannich/Michael tandem reaction of the resulting sugar imine with Danishefsky’s diene. The stereochemical course of the investigated reaction has been explained in detail
Sugar-derived cyclic nitrones were synthesized from the corresponding aldoses through an efficient and practical procedure involving a seven-step reaction sequence in good to excellent overall yield (10-42%). This synthetic strategy, requiring only inexpensive reagents, is easy to perform and hence suitable for large-scale preparations.
A systematic study of diastereoselective nucleophilic addition of Grignard reagents to six-membered chiral tri-O-benzyl cyclicnitrones is described. With all eight chiral cyclicnitrones and asymmetric reaction conditions in hand, a practical methodology is established for the preparation of diverse 1-deoxyazapyranosides bearing various stereogenic centers.
Generation and fragmentation of the C1-alkoxy radicals of pyranosederivatives are nicely promoted by (diacetoxyiodo)benzene or lead tetraacetate in the presence of iodine catalyst under mild conditions to give the corresponding mixed-acetal formates which are further converted to the furanosederivatives by acid-catalysed transacetalization.
Regioselective and Diastereoselective Amination of Polybenzyl Ethers Using Chlorosulfonyl Isocyanate: Total Syntheses of 1,4-Dideoxy-1,4-imino-<scp>d</scp>-arabinitol and (−)-Lentiginosine
作者:In Su Kim、Ok Pyo Zee、Young Hoon Jung
DOI:10.1021/ol061614x
日期:2006.8.1
The total syntheses of DAB1 (1) and (-)-lentiginosine (2) were concisely accomplished from D-lyxose via regioselective and diastereoselective NHCbz introduction using CSI, chemoselective removal of the Cbz protection, and ring-closing metathesis as key steps.