29 短工程かつ実用的な麦角アルカロイド全合成
詳細
We have now established a common and practical short step synthetic method, as shown in chart 5, which is widely applicable for various ergot alkaloids and their analogs only by changing a reagent in each step and without changing the reaction type. Thus, when 2-methyl-3-buten-2-ol is used as an olefin in the second step, X, L, R^1, and R^2 of the formulas in chart 5 are I, OH, H, and H, respectively, and (±)-6,7-secoagroclavine (9) was synthesized in 36% overall yield. In the case of using 2-methoxy-2-methyl-3-buten-1-ol as an olefin, X, L, R^1, and R^2 are I, OMe, OH, and H, respectively, and (±)-6-norchanoclavine-I (20 or G) and (±)-6-norisochanoclavine-I (23 or G, R^1=H, R^2=OH) were obtained in good overall yields. These synthetic alkaloids were readily converted to (±)-chanoclavine-I (22 or I) or (±)-isochanoclavine-I (25 or I, R^1=H, R^2=OH), respectively. Treatment of 25 with thionyl chloride produced (±)-agroclavine (26). Since the alkaloid (26) has already been led to festuclavine, costaclavine, setoclavine, and isosetoclavine, formal syntheses of these alkaloids were also achieved. For the syntheses of above mentioned ergot alkaloids in large quantity, experimental procedures were extensively examined and now we can carry out successfully each of all steps involved in chart 1 in 50g scale.
