A Practical Synthesis of N-(4-Isopropyl-2,2-dimethyl-3-oxo-3,4 dihydro-2H-benzo(1,4)oxazine-6-carbonyl)guanidine Methanesulfonate (KB-R9032) Utilizing Potassium Fluoride-Alumina Catalyzed N-Alkylation.
作者:Takeshi YAMAMOTO、Manabu HORI、Ikuo WATANABE、Hisayoshi TSUTSUI、Shoji IKEDA、Hiroshi OHTAKA
DOI:10.1248/cpb.46.1317
日期:——
N-Isopropylation of methyl 2, 2-dimethyl-3-oxo-3, 4-dihydro-2H-benzo[1, 4]oxazine-6-carboxylate (2a) with various reagents was examined in order to prepare 3a, the key intermediate in the synthesis of N-(4-isopropyl-2, 2-dimethyl-3-oxo-3, 4-dihydro-2H-benzo[1, 4]oxazine-6-carbonyl)guanidine methanesulfonate (1, KB-R9032), a novel, potent Na/H exchange inhibitor. When a base such as sodium hydride, potassium carbonate or potassium tert-butoxide was used, the undesired O-isopropyl derivative 4a was produced as the main product. Among the hydrogen bond assisted mild bases examined, potassium fluoride (KF)-alumina afforded the best N-/O-selectivity with a ratio of about four. The undersired O-isopropyl derivative 4a could be easily converted to the starting 2a under non-aqueous acidic conditions. Combination of the above two processes increased the N-/O-ratio (to about 42). Consequently, the N-isopropyl derivative 3a was isolated without column chromatography in more than 70% yield. This KF-alumina catalyzed repeated isopropylation was applicable to N-selective alkylation of other hindered cyclic amides to afford N-alkyl derivatives in high yields.
研究了 2,2-二甲基-3-氧代-3,4-二氢-2H-苯并[1,4]恶嗪-6-羧酸甲酯(2a)与各种试剂的 N-异丙基化反应,以制备 3a、3a,这是合成新型强效 Na/H 交换抑制剂 N-(4-异丙基-2,2-二甲基-3-氧代-3,4-二氢-2H-苯并[1,4]恶嗪-6-甲酰基)甲磺酸胍(1,KB-R9032)的关键中间体。当使用氢化钠、碳酸钾或叔丁醇钾等碱时,主要生成物为不需要的 O-异丙基衍生物 4a。在所研究的氢键辅助温和碱中,氟化钾(KF)-氧化铝的 N/O 选择性最好,比例约为 4。在非水酸性条件下,未充分反应的 O-异丙基衍生物 4a 可以很容易地转化为起始产物 2a。将上述两个过程结合起来,N-/O-选择性比率就会提高(约为 42)。因此,不用柱层析就能分离出 N-异丙基衍生物 3a,收率超过 70%。这种 KF-氧化铝催化的重复异丙基化反应适用于其他受阻环酰胺的 N-选择性烷基化反应,以获得高产率的 N-烷基衍生物。