A. C 2e Sterol
59
among the more primitive phyla was expressed by Bergmann (1949, 1962),
although the full extent of this recognition was not realized until after his
death because the necessary research tools were not available earlier. Bergmann
furthermore possessed a great deal of intuitive know-how about sterol
chemistry, and he suspected unusual structural features that he, through no
fault of his, was unable to prove. In marine sterol research three independent
factors have converged leaving considerable doubt about the correctness
of much of the early work. First, the remarkable diversity and complexity
of marine sterol mixtures. Second, the notorious ability of even complex
sterol mixtures to crystallize easily and well and to melt within a narrow
range. Third, the monotony of elemental composition of sterols, which
has rendered virtually all marine sterol research prior to about 1960
subject to serious doubt. Notable exceptions to this generalization are the
fortuitous cases in which natural sterol mixtures were either relatively
simple or they contained one predominant constituent. In those cases resolution of the mixture was feasible by column chromatography, particularly
when the separation was carried out via the colored 4-azobenzenecarboxylates, a method that was first introduced in 1938 (Ladenburg et al.), but was
fashioned into a viable experimental tool by Idler and Baumann (1952).
Because of these circumstances well-authenticated, largely recent work will
receive major emphasis in the discussion that follows. A recent general
review that includes marine sterols was published in 1970 (Brooks, 1970),
but none of the more current work of great interest is covered, because of the
normal time lag between manuscript and published book. In addition,
sterols of invertebrates have been reviewed by Austin (1970) molluscan
sterols by Idler and Wiseman (1972), echinoderm sterols by Goad and coworkers (1972), and crustacean sterols by Idler and Wiseman (1971). Much
new research on marine sterols is now in progress.
Arrangement of the material according to carbon content appears to be
simple and straightforward, although carbon content per se is no longer
considered to be a significant property. For many years the carbon range of
sterols extended from C 27 to C 29 , but recent discoveries of a norcholesterol
and of gorgosterol and its analogs have increased the carbon range of marine
sterols from C 26 to C 3 0 ; yet even now C 29 sterols predominate. It is worth
noting that the carbon variation occurs exclusively in the side chain,* and
not unexpectedly most of it at C-24. What structural diversity other than
carbon content exists among marine sterols is almost entirely found in the
side chain also, with the notable exception of the highly oxygenated C 27
moulting hormones (Section 2, B,6) and of some bile alcohols (Section 2, B,9).
* Gibbons et al. (1968) in their study of the green algae Enteromorpha intestinalis and
Ulva lactuca report indications of the presence of lophenol (a 4-methylsterol) derivatives.
None of these has as yet been isolated.
59
among the more primitive phyla was expressed by Bergmann (1949, 1962),
although the full extent of this recognition was not realized until after his
death because the necessary research tools were not available earlier. Bergmann
furthermore possessed a great deal of intuitive know-how about sterol
chemistry, and he suspected unusual structural features that he, through no
fault of his, was unable to prove. In marine sterol research three independent
factors have converged leaving considerable doubt about the correctness
of much of the early work. First, the remarkable diversity and complexity
of marine sterol mixtures. Second, the notorious ability of even complex
sterol mixtures to crystallize easily and well and to melt within a narrow
range. Third, the monotony of elemental composition of sterols, which
has rendered virtually all marine sterol research prior to about 1960
subject to serious doubt. Notable exceptions to this generalization are the
fortuitous cases in which natural sterol mixtures were either relatively
simple or they contained one predominant constituent. In those cases resolution of the mixture was feasible by column chromatography, particularly
when the separation was carried out via the colored 4-azobenzenecarboxylates, a method that was first introduced in 1938 (Ladenburg et al.), but was
fashioned into a viable experimental tool by Idler and Baumann (1952).
Because of these circumstances well-authenticated, largely recent work will
receive major emphasis in the discussion that follows. A recent general
review that includes marine sterols was published in 1970 (Brooks, 1970),
but none of the more current work of great interest is covered, because of the
normal time lag between manuscript and published book. In addition,
sterols of invertebrates have been reviewed by Austin (1970) molluscan
sterols by Idler and Wiseman (1972), echinoderm sterols by Goad and coworkers (1972), and crustacean sterols by Idler and Wiseman (1971). Much
new research on marine sterols is now in progress.
Arrangement of the material according to carbon content appears to be
simple and straightforward, although carbon content per se is no longer
considered to be a significant property. For many years the carbon range of
sterols extended from C 27 to C 29 , but recent discoveries of a norcholesterol
and of gorgosterol and its analogs have increased the carbon range of marine
sterols from C 26 to C 3 0 ; yet even now C 29 sterols predominate. It is worth
noting that the carbon variation occurs exclusively in the side chain,* and
not unexpectedly most of it at C-24. What structural diversity other than
carbon content exists among marine sterols is almost entirely found in the
side chain also, with the notable exception of the highly oxygenated C 27
moulting hormones (Section 2, B,6) and of some bile alcohols (Section 2, B,9).
* Gibbons et al. (1968) in their study of the green algae Enteromorpha intestinalis and
Ulva lactuca report indications of the presence of lophenol (a 4-methylsterol) derivatives.
None of these has as yet been isolated.