Scheme 21 Synthesis of asperlicin [242]

Epoxidation of 95 with Davis' oxaziridine reagent [214,215], followed by NaBH4 reduction and DDQ oxidation affords 96, which upon deprotection by hydrogenolysis gives asperlicin 20 (15 steps from L-tryptophan with 8% overall yield).

Total synthesis of asperlicin C and E via condensation route by Bock et al. is well known [76-79,243]. The first total synthesis of asperlicin D via both cyclodehydration and intramolecular aza-Wittig routes has been fulfilled very recently by Al-Said et al. [244], and the iminophosphorane intermediates having secondary amide protons have been shown to provide a one-step entry to quinazolino[1,4]benzodiazepine ring system like asperlicin D (a positional isomer of asperlicin C). A facile route to N-benzylsclerotigenin has been reported also by this group [245]. On the other hand, total synthesis of circumdatin F (19) (and circumdatin C) via dehydrative cyclization (or ben-zoxazine) route has been also fulfilled by Bergman et al. [246].

Pyrazinoquinazoline Alkaloids

Several groups of quinazoline alkaloids involving pyrazino[2,1-fr]quinazoline-3,6-dione substructure are found in fungal metabolites. These include glyantrypine (21) [87], fumiquinazolines A-E, F (22), G (23) [88,89], H and I [90], and fiscalines A-C [91,92]. Novel spiro-type pyrazinoquina-

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