5
NONAROMATIC COMPOUNDS WITH
UNRRANCHED CARBON SKELETONS
As has been pointed out in the Preface, the group of compounds to
be discussed in this chapter is perhaps the least coherent and therefore the
most controversial in the book. Although few chemists will argue whether a
given natural product should be classified as a steroid or an alkaloid, it can
become a matter of dispute whether to include branched fatty acids and their
derivatives (the so-called iso acids for example) among the compounds
possessing "unbranched carbon skeletons." (On the other hand, unbranched
benzenoid compounds have been deliberately omitted from discussion here
and are being treated in a separate chapter.) Presumably, these branched
compounds have arisen biogenetically from an occasional propionate residue
being condensed with a preponderance of acetate fragments. All of these
compounds are included in this chapter provided they are distinctly not of
isoprenoid origin, nor have aromatic character. Generally, a positive criterion
would be preferable, but no such simple designation embracing these compounds occurs to me.
A. Fatty Acids
There are a number of reasons why the chemistry of fatty acids will
receive only summary mention rather than detailed discussion. Most importantly, unmodified fatty acids are not natural products in the historical
168
NONAROMATIC COMPOUNDS WITH
UNRRANCHED CARBON SKELETONS
As has been pointed out in the Preface, the group of compounds to
be discussed in this chapter is perhaps the least coherent and therefore the
most controversial in the book. Although few chemists will argue whether a
given natural product should be classified as a steroid or an alkaloid, it can
become a matter of dispute whether to include branched fatty acids and their
derivatives (the so-called iso acids for example) among the compounds
possessing "unbranched carbon skeletons." (On the other hand, unbranched
benzenoid compounds have been deliberately omitted from discussion here
and are being treated in a separate chapter.) Presumably, these branched
compounds have arisen biogenetically from an occasional propionate residue
being condensed with a preponderance of acetate fragments. All of these
compounds are included in this chapter provided they are distinctly not of
isoprenoid origin, nor have aromatic character. Generally, a positive criterion
would be preferable, but no such simple designation embracing these compounds occurs to me.
A. Fatty Acids
There are a number of reasons why the chemistry of fatty acids will
receive only summary mention rather than detailed discussion. Most importantly, unmodified fatty acids are not natural products in the historical
168