P-35 窒素原子が結合した不斉四級炭素をもつ海洋天然物の合成研究(ポスター発表の部)

抄録

The isonitrile analogue of diterpenoid geranyllinalool was isolated by Scheuer during a screening program for bioactive constituents from marine sponges Halichondria sp. as an active compound against Staphylococcus aureus. This molecule possesses a unique isonitrile-containing quaternay carbon at C-3. The nitrogen-substituted quaternary stereocenter was planned to constuct by [3.3] sigmatropic rearrangement of allyl cyanate. Starting with D-lactic acid methyl ester, allyl alcohol was prepared and then was transformed into allyl carbamate, dehydration of which was carrid out by using the modified Appel's conditions (PPh_3, CBr_4, Et_3N, CH_2Cl_2, -10℃) to generate allyl cyanate, which immediately underwent [3.3] sigmatropic rearrangement at -10℃ to afford allyl isocyanate. After careful work-up, the isolated isocyanate was treated with lithium tert-butoxide in THF. Further transformation of the resultant Boc-carbamate and synthesis of opticallyl active geranyllinalool isocyanide will be presented. Manzacidins A and C were isolated and its structure was determined by Kobayashi. The first synthesis of manzacidins A and C were reported by Ohfune, who established the stereochemistry by total synthesis. The most critical problem in the synthesis of manzacidins is the construction of quaternary stereogenic center attached nitrogen. Retrosynthetic analysis showed that dehydration of carbamate would generate the allyl cyanate, which will undergo [3,3] sigmatropic rearrangement to construct the quaternary stereogenic center attaced nitrogen. The isocyanate could be transformed to the Boc-carbamate by the reaction with tert-butanol. Further details of our synthetic studies of manzacidins will be reported.