Cyclopropane fatty acids (CPA) are a subgroup of
fatty acids
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...
that contain a
cyclopropane
Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself i ...
group. Although they are usually rare, the seed oil from
lychee
Lychee (US: ; UK: ; ''Litchi chinensis''; ) is a monotypic taxon and the sole member in the genus ''Litchi'' in the soapberry family, ''Sapindaceae''.
It is a tropical tree native to Southeast and Southwest China (the Guangdong, Fujian, Yunn ...
contains nearly 40% CPAs in the form of
triglyceride
A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and '' glyceride'').
Triglycerides are the main constituents of body fat in humans and other vertebrates, as ...
s.
Biosynthesis
CPAs are derived from unsaturated fatty acids by
cyclopropanation
In organic chemistry, cyclopropanation refers to any chemical process which generates cyclopropane () rings. It is an important process in modern chemistry as many useful compounds bear this motif; for example pyrethroids and a number of quinolon ...
. The methylene donor is a methyl group on
S-adenosylmethionine
''S''-Adenosyl methionine (SAM), also known under the commercial names of SAMe, SAM-e, or AdoMet, is a common cosubstrate involved in methyl group transfers, transsulfuration, and aminopropylation. Although these anabolic reactions occur throu ...
(SAM). The conversion is catalyzed by
cyclopropane-fatty-acyl-phospholipid synthase. The mechanism is proposed to involve transfer of a CH
3+ group from SAM to the
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
, followed by deprotonation of the newly attached methyl group and ring closure.
Cyclopropene fatty acids
Cycloprop''e''ne fatty acids are even rarer than CPAs. The best-known examples are
malvalic acid and
sterculic acid. Sterculic acid as its triglyceride is present in sterculia oils and at low levels in
kapok seed oil (~12%),
cottonseed oil
Cottonseed oil is cooking oil from the seeds of cotton plants of various species, mainly '' Gossypium hirsutum'' and ''Gossypium herbaceum'', that are grown for cotton fiber, animal feed, and oil.
Cotton seed has a similar structure to other oi ...
(~1%), and in the seeds of the tree ''
'' (~65-78%). These acids are highly reactive but the cyclopropene ring is destroyed during refining and hydrogenation of the oils. They have attracted interest because they reduce levels of the enzyme
stearoyl-CoA 9-desaturase
Stearoyl-CoA desaturase (Δ-9-desaturase) is an endoplasmic reticulum enzyme that catalyzes the rate-limiting step in the formation of monounsaturated fatty acids (MUFAs), specifically oleate and palmitoleate from stearoyl-CoA and palmitoyl-C ...
(SCD), which catalyzes the biodesaturation of
stearic acid
Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a waxy solid and its chemical formula is C17H35CO2H. Its name comes from the Greek word στέαρ "''stéar''", which means tall ...
to
oleic acid
Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated om ...
.
At least one review indicates that CPFA are
carcinogenic
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...
,
co-carcinogenic
A co-carcinogen is a chemical that promotes the effects of a carcinogen in the production of cancer. Usually, the term is used to refer to chemicals that are not carcinogenic on their own, such that an equivalent amount of the chemical is ins ...
, and have medical and other effects on animals;
[L. O. Hanus, P. Goldshlag, V. M. Dembitsky (2008). IDENTIFICATION OF CYCLOPROPYL FATTY ACIDS IN WALNUT (JUGLANS REGIA L.) OIL. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub. 2008, 152(1):41–45.] according to this review, "CPFA in food is dangerous to human health".
References
External links
* {{cite journal , doi = 10.1073/pnas.092152999 , pmid = 11997456 , pmc = 124547 , url = http://www.pnas.org/cgi/reprint/99/10/7172.pdf , title = Carbocyclic fatty acids in plants: Biochemical and molecular genetic characterization of cyclopropane fatty acid synthesis of Sterculia foetida , journal = Proceedings of the National Academy of Sciences , volume = 99 , issue = 10 , pages = 7172–7177 , year = 2002 , last1 = Bao , first1 = X. , last2 = Katz , first2 = S. , last3 = Pollard , first3 = M. , last4 = Ohlrogge , first4 = J. , bibcode = 2002PNAS...99.7172B , doi-access = free
Fatty acids
Cyclopropanes