No abstract

An efficient total synthesis of thalicarpine (13b), a tumor-inhibitory aporphine benzylisoquinoline alkaloid, is described. The diaryl ether (8a), prepared from lb and 4a, was condensed with the 3,4-dihydroisoquinolinium salt 2a to give 9a. Reduction of 9a, followed by diazotization in phosphoric acid and heating, yielded the aporphine 10a and the phenol 9h. Formylation of 10a gave (±)-hernandaline (10b), which was resolved with (+)-a-bromocamphor-7T-sulfonic acid. The overall yield of the hernandaline precursor 10a was improved by a reaction sequence involving the phenolic intermediates 2b, 9f, 9g, and 10c. Hernandaline (10b, S configuration) was condensed with the Reissert compound 5 and the product (12) was reduced with zinc in acetic acid to a mixture of nor bases (13a and epimer). Methylation with formalin-formic acid gave thalicarpine (13b).

Summary. The specific binding activity to [laC]thiamine was found to be located in the plasma membrane of Saccharomyces cerevisiae. The activity was inhibited by several thiamine analogs and it was hardly detectable in the plasma membrane from a thiamine transport mutant of Saccharomyces cerevisiae. Some properties of the thiamine-binding activity of yeast plasma membrane are discussed in connection with those of the thiamine transport system.

No abstract

The addition of a carboxyl-modifying reagent N,N'-dicyclohexylcarbodiimide (DCCD) to thiamine-binding protein isolated from rice bran resulted in a remarkable loss of its binding activity with [14C]thiamine. Thiamine and chloroethylthiamine substantially protected the protein against inactivation by DCCD, whereas thiamine phosphates did not. Another carboxyl reagent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) also inactivated rice bran thiamine-binding protein. Inactivation of the thiamine-binding protein was accompanied by covalent binding of DCCD to the protein as shown by the use of [14C]DCCD. The binding of [14C]DCCD to the thiamine-binding protein was specific, and significantly inhibited by the addition of thiamine. The loss of thiamine-binding activity was proportional to the specific binding of [14C]DCCD. For complete inactivation of the thiamine-binding activity, the binding of 2.46 mol of [14C]DCCD per mol of thiamine-binding protein was required. Furthermore, limited proteolysis of the binding protein by trypsin yielded two polypeptides with molecular weights of 35,000 (large polypeptide) and 12,500 (small polypeptide) which were separated by SDS-polyacrylamide gel electrophoresis. The binding sites of [14C]DCCD were found to be located on the large polypeptide. These results suggest that a specific carboxyl residue in the large polypeptide releasable from rice bran thiamine-binding protein by trypsin digestion when modified by DCCD is involved in the binding of thiamine.