In a method for spectrophotometric determination of ergosterol in yeast samples containing 5 to 100 mg. of yeast solids, the yeast is digested with alcoholic alkali and ergosterol is extracted in a single extraction with a measured volume of pure n-heptane. Absorbances at 281.5 and 230 µ are determined on an aliquot of the heptane diluted in absolute ethyl alcohol. Amount of "ergosterols" are determined from the 281.5-µ measurement, and amount of 24(28)-dehydroergosterol is determined from the 230-µ measurement.

Ergosterol has long been known as the primary sterol of yeast (1) and several other yeast sterols have been reported. Smedley-MacLean (2) reported the presence of zymosterol, a dextrorotatory sterol. The structure of zymosterol was long in question until Barton (3) showed it to be 8,24-cholestadien-3/3-ol. As a consequence of the establishment of the zymosterol structure and from the recent development of theories concerning optical rotation and structure, it would appear that two other dextrorotatory sterols of yeast reported by Wieland and others (4), namely ascosterol and fecosterol, are also unsaturated at the 8(9) position. Callow (5) reported the occurrence in yeast of "a-dihydroergosterol", since shown to be 5-dihydroergosterol (6). The neosterol described by Wieland (4) appears from the work of Barton ( 7) to be a mixture of 5-dihydroergosterol and ergosterol. Cerevisterol, described by Honeywell and Bills (8) has recently been shown (9) to be 7,22-ergostadiene-3/3,5 , 6,5-triol. It therefore appears to be an oxidation product of ergosterol, but whether it is formed metabolically by yeast or whether it is formed from ergosterol by chemical oxidation during isolation of the sterols, is not clear. Wieland and Gough (10) have also described two other yeast sterols, episterol and hyposterol.The new yeast sterol we wish to report is a tetraethenoid sterol having a ring structure identical with that of ergosterol, and having a conjugated double bond system in the side chain. Although the position of the conjugated double bond system in the side chain has not been positively established, the ultraviolet and infrared absorption characteristics lead us to believe that the new sterol has one of the structures (I or II) shown. The location of the ultraviolet maximum at 230 µ and the infrared band at 11.3 µ lend credence to the presence of a vinylidene group (11). It may further be reasonable to assume that since the new sterol is a metabolic product of yeast, the enzyme systems which are involved in production of ergosterol and zymosterol would be more likely to place a second double bond in ergosterol at 24(28) than at 20(21). Hence we favor structure I and tentatively designate the new sterol as 24(28)-dehydroergosterol, or 5,7,22,24 (28)-ergostatetraen-3#3-ol. SUMMARYThe isolation of a new tetraethenoid sterol from yeast is described. Its concentration in some yeasts approximates the ergosterol content. On the basis of chemical and spectroscopic evidence, its structure is proposed to be 5,7,22,24-(28)-ergostatetraen-30-ol.Stamford, Conn.