Isolation and structure of oxirapentyn.

Sir: A new antibiotic, oxirapentyn was isolated from the culture broth of fungus identified as Beauveria felina SANK 13682. It was characterized to have a new skeleton with two isoprene units and an activity against Gram-positive bacteria. In this paper we report the isolation, biological activities and structure of oxirapentyn. Oxirapentyn was produced in a shaken culture of B. felina SANK 13682 for 3 to 5 days at 26°C in a medium containing 2 % sucrose, 2.5 % mashed potatoes, 1 % Casamino Acids, 0.5 % KH2PO4 and 0.25% MgSO4 • 7H2O. The culture filtrate (8.7 liters) was extracted with ethyl acetate (9 liters) and the solvent layer was concentrated in vacuo to syrup. This syrup was dissolved in 10 ml of benzene ethyl acetate (9: 1) and further purified by silica gel column chromatography. The active fractions were concentrated to yield the crude oxirapentyn. The pure oxirapentyn (1.3 g) was obtained by recrystallization from the solvent mixture of hexane ethyl acetate as colorless needles. Oxirapentyn (1): soluble in methanol, acetone, ethyl acetate, and chloroform and insoluble in water; mp 114~115'C; Anal. calcd. for C18H20O6: C 65.05, H 6.07, found: C 65.42, H 6.05; MS m/z 332 (M+); UV 2MeOHmax n (E1%1cm) 225 (480); [a]20D -111.7° (c 1, CHCl3); IR vKBrmax 2230 (triple bond), 1740 (acetyl), 1710 (ketone) and 1608 cm-1 (double bond). The 1H and 13C NMR spectra of 1 are shown in Figs. 1 and 2. The complete structure of 1 was determined by JCC coupling and the long-range JCH, resolved 2-D method in the NMR spectrum, the result of which will be discussed elsewhere. However, the structure of 1 with its relative configuration was elucidated by means of X-ray analysis as follows: The crystals are trigonal, space group P3121 (or P3,21) with a=11.078 (2), c=25.170 (4) A, Z=6. Intensity data were measured on a Rigaku AFC-5 apparatus equipped with a rotating-anode X-ray generator (graphite-monochromated Cu-Ka radiation). The structure was solved by MULTANI) and refined by block-diagonal least-