[CONTRIBUTION FROM
THE
STERLING CHEMISTRY LABORATORY AND LABORATORY, Y A L E UNIVERSITY ]
THE
BINGHAM
OCEANOGRAPHIC
CONTRIBUTIONS TO THE STUDY OF MARINE PRODUCTS. XX. REMARKS CONCERNING THE STRUCTURE OF STEROLS FROM MARINE INVERTEBRATES ERNER BERGMA”
AND
EVA M. LOW
Receiued June 10, 1946
I n 1941, Fernholz and Ruigh (1) convincingly demonstrated that campesterol and campestanol differ from 22,23-dihydrobrassicasteroland ergostanol solely in the optical configuration at C-24. Since then it has been shown that this C-24 epimerism is not infrequently encountered among naturally occurring sterols, and that the Css-sterols from marine invertebrates such as the stellasterols and stellastenols (21, neospongosterol (3) and chalinasterol (4) predominantly belong to the campestanol series. In conformity with the customary designation of steroid epimers, it is here proposed to refer to the ergostanol and campestanol series as the 24-(a)- and 24-(p)-methylcholestanol series, and following a suggestion by Ruigh ( 5 ) , to write the 24-methy1 group above the side chain in the a-series (I) and below the side chain in the p-series (11). CH,
I
R
I
HCCHz CH2 CHCH(CH3)z I
22,23-Dihydrobrassicasterol,R = CHs CH3 HCCH2CH2CHCH(CHa)2 I
I
11. C-24p-Sterol Campesterol, R = CHI 67
68
WERNER BERGMANN AND EVA M. LOW
Sufficient data have now become available for the rotations of various representatives of both series to permit an evaluation of the contributions of the 24-a- and 24-P-methyl groups to the molecular rotations.' As has been shown by Callow and Young (6), Wallis and co-workers (7), and recently also by Barton (8), examination of differences in molecular rotations of steroids frequently provides a useful tool in establishing the structure of a steroid or its uniformity. TABLE I hfOLECULAR
ROTATIONS OF
THE CHOLESTANOL AiTD 24-hfETHYLCHOLESTAKOL S E R I E S
i
I Stanylacetate ...................... $60 5,6-Stenol., . . . . . . . . . . . . . . . . . . . . . . . -151 5,6-Stenylacetate. . . . . . . . . . . . . . . . . . -184 5,6-Stenylbenzoate.. . . . . . . . . . . . . . . -64
+27 -184 -203 -96
1 1
I ~
-29 -33 -33 - 19 -32
+80 -132 -159 -50
Average, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . a
-29
~
1
j 1
+32 +20 +19 +a5 $14 +22
Molecular rotations according to Barton (8).
MOLECULAR
TABLE I1 ROTATIONS OF THE 8,14-
AND
MID^ COXPOUND
Cholestanol
! 8,14-Senol.. ...................... 8,14&enylacetate., . . . . . . . . . . . . . . . 8,14-Stenylbenzoate... . . . . . . . . . . .
,1
.I
14,15-STENOLS
I
1 24-a-Methyl I 24-@-Methyl
I +81 +43 +39
+4 +5
j
' -33 -39 -34 .......
-52 -63 - 56
A2 ~
1
I
-1
+14
1
Iik;i -10
_ _ _ _ _ _ ~ 6
Molecular rotations according to Barton (8).
In Table I the molecular rotations of cholestanol and its derivatives are compared with those of 24-a- and 24-B-methyl cholestanol and their corresponding derivatives. The figures A, and A2 represent the differences in molecular rotations between the series cholestanol : 24-a-methylcholestanol (ergostanol) and cholestanol : 24-~-methylcholestanol(campestanol). It may be seen that the presence of a 24-a-methyl group increases the levo-rotation by a comparatively uniform value, the average A, = -29. In the absence of "vicinal action" it is to be expected that a 24-p-methyl group increases the dexbro-rotation and that the average A, = +29. The observed average value for A2 = +22 agrees quite Molecular Rotation, [MI,
[el0 X
Mol. weight 100
STUDIES O F MARINE PRODUCTS.
XX
69
well with this expectation, particdarly since the permissible error in molecular rotation8 is f 10. At present the data for the a-series appear to be more accurate than those for the @-series. In the latter, considerable difficulties are frequently encountered in obtaining products free from the more levo-rotatory a-epimers. Table I1 contains a comparison of the molecular rotations of the corresponding 8,14- and 14,15-stenols (8). The average AI = -35 for the 8,l$-stenols agrees fairly mll with the corresponding value in Table I. The A2-values,however, which are based on the rotations reported for “a”-stellastenol (2) are unsatisfactory. They suggest either that “a”-stellastenol does not possess the structure or that it contains significant quantities of the of a 24-methylcholesten-8,14-01, more levo-rotatory 24-a-methyl epimer. On the basis of other evidence (4), the latter possibility appears to be more probable. The calculated values for the specific rotations of 24-@-methylcholesten-8,14-01and its acetate are +26.5” and +17.5”, and those reported for ‘26). (29) A N D E R S O N , S H R I N E R , AND BURR,J.A m . Chem. SOC., 48,2987 (1926). (1) (2) (3) (4) (5) (6) (7)
