A new β-carboline alkaloid from the Streptomyces flocculus CGMCC4.1223 mutant ΔstnK4

Synthesis of Canthin-4-ones and Isocanthin-4-ones via B Ring Construction

“…Calcd for C 15 H 10 N 2 O: C,76.91;H,4.30;N,11.96. Found: C,77.02;H,4.26;N,2,5]naphthyridin-4-one (8c). 2-Chloro-4-methoxyphenylboronic acid (83.9 mg, 0.45 mmol) gave compound 8c (chromatography eluent, 50:50 EtOAc/THF) as pale yellow needles (26.5 mg, 35%): mp (DSC) onset 298.2 °C, peak max 301.0 °C, decomposition peak max 302.9 °C (EtOH); R f = 0.18 (THF); λ max (DCM, nm) 259 inf (log ε = 4.26), 264 (4.29), 284 inf (4.28), 293 (4.45), 299 (4.48), 345 (4.10), 373 (4.16); v max (ATR, cm −1 ) 3032w (aryl C−H), 1641m, 1607s (C�O), 1557m, 1510s, 1477m, 1470m, 1454m, 1441m, 1431m, 1329m, 1310m, 1275w, 1227s, 1192m, 1175m, 1163m, 1115m, 1069w, 976w, 868m, 853m, 826m, 802m, 793m 2 (s), 162.3 (s), 146.8 (d), 140.8 (s), 137.9 (s), 135.0 (s), 133.6 (d), 133.3 (s), 124.9 (d), 116.54 (s), 116.47 (d), 112.4 (d), 97.3 (d) ), 1643m, 1618m, 1593m, 1555m, 1506m, 1483m, 1445m, 1430m, 1329m, 1300m, 1273m, 1229m, 1190m, 1152m, 1121w, 1084w, 1024m, 953m, 912m, 862m, 849m, 824s, 793w, 756m 11.76.…”

“…The latter was only recently isolated from a mutant ΔstnK4 of Streptomyces f locculus CGMCC4, and its structure elucidated by extensive one-and two-dimensional nuclear magnetic resonance (NMR). 5 Several syntheses for norisotuboflavine, 6 isotuboflavine, 7 and tuboflavine 8 have been reported. In 1966, Schmid et al reported a four-step synthesis for tuboflavine, starting from tryptophan in 0.3% overall yield, 7 while in 1968, they reported the syntheses of norisotuboflavine and isotuboflavine, 6 in three steps starting from 4,5-dihydrocanthin-6-one in <1% overall yield.…”

“…Canthin-4-ones represent the lesser-known family of canthine alkaloids, the most well-known of which are the canthin-6-ones . More than 60 natural analogues of canthin-6-ones have been isolated to date, but only four natural analogues of canthin-4-ones are known: tuboflavine, norisotuboflavine, isotuboflavine, and oxoproopaline H (Figure ). The latter was only recently isolated from a mutant ΔstnK4 of Streptomyces flocculus CGMCC4, and its structure elucidated by extensive one- and two-dimensional nuclear magnetic resonance (NMR) …”

“…The latter was only recently isolated from a mutant ΔstnK4 of Streptomyces flocculus CGMCC4, and its structure elucidated by extensive one- and two-dimensional nuclear magnetic resonance (NMR). 5 …”