SERIAL REVIEWS I
`
`in relation
`
`to
`
`and properties
`
`Structure
`function
`GEORGE BRITFON’
`of Biochemistry, University of Liverpool. Liverpool, United Kingdom
`Department
`
`of carotenoids
`
`in
`a
`of
`
`are widespread
`which
`carotenoids,
`all
`Essentially
`chemical
`features:
`certain
`common
`nature,
`possess
`conjugated
`chain
`structure,
`a long
`polyisoprenoid
`in the
`central
`portion
`of
`the molecule,
`double
`bonds
`and
`near
`symmetry
`aroutid
`the
`central
`double
`bond.
`This
`basic
`structure
`can
`be modified
`in a variety
`of
`ways, most
`prominently
`by cyclization
`of
`the
`end
`groups
`and
`by the
`imitroduction
`of oxygen
`functions,
`to
`yield
`a large
`faniily
`of >600
`compounds,
`exclusive
`of
`isomers.
`They
`perform important
`functions
`in
`cis/trans
`nature,
`including
`light-harvesting,
`photoprotection,
`protective
`and
`sex-related
`coloration
`patterns
`in niany
`animal
`species,
`and
`as precursors
`of vitamin A in ver-
`tebrates.
`They may
`serve
`protective
`roles
`as well
`against
`age-related
`diseases
`imi humans
`as part
`of a
`complex
`antioxidant
`network within
`cells.
`In this open-
`ing review,
`emphasis
`is placed
`on the
`close
`relation-
`ship
`between
`the
`physicochemical
`properties
`carotemioids
`and their
`functions
`and actions
`in nature.
`James A. Olson, Coordinating
`Editor
`
`of
`
`The
`
`structure,
`of
`principles
`basic
`ABSTRACT
`carotenoids
`of
`and
`nomenclature
`stereochemistry,
`between
`struc-
`the
`relationships
`and
`are
`described
`properties
`on
`chemical
`and
`physical
`ture
`and
`the
`and actions
`which
`all
`the varied
`biological
`functions
`conjugated
`of carotenoids
`depend
`are discussed.
`The
`polyene
`chromophore
`determines
`not
`only
`the
`light
`absorption
`properties,
`and hence
`color,
`but also
`the
`photochemical
`properties
`of
`the molecule
`and con-
`sequent
`light-harvesting
`and photoprotective
`action.
`The polyene
`chain
`the
`feature mainly
`respon-
`is also
`sible
`for
`the
`chemical
`reactivity
`of
`caroteitoids
`to-
`ward
`oxidizing
`agents
`and
`free
`radicals,
`and hence
`for
`any
`antioxidant
`role.
`In vivo,
`carotenoids
`are
`in precise
`locations
`and orientations
`in s,ihcel-
`found
`lular
`structures,
`and
`their
`chemical
`physical
`and
`by
`properties
`are
`strongly
`influenced
`other mole-
`proteins
`cules
`their
`vicinity,
`especially
`and mem-
`iii
`brane
`lipids.
`In turn,
`the
`carotenoids
`influence
`the
`properties
`of these
`subcellular
`structures.
`Structural
`features
`such as size,
`and polarity
`are essential
`shape,
`fit
`determinants
`of
`the
`ability
`of
`a carotenoid
`to
`correctly
`its molecular
`environment
`to allow it
`to
`function.
`A role
`for
`carotenoids
`in modifying
`structure,
`properties,
`and
`stability
`of
`cell mem-
`
`into
`
`molecular
`affecting
`and thus
`branes,
`with these membranes,
`may
`ciated
`of
`their
`possible
`beneficial
`aspect
`health.-Britton,
`G. Structure
`rotenoids
`in relation
`to function.
`1558
`(1995)
`
`asso-
`processes
`be an important
`effects
`on human
`and properties
`of ca-
`FASEB J. 9, 1551-
`
`light
`Key Words:
`!ein in/era c/ions
`
`absorption
`membranes
`
`.
`
`. carotenoid-pro-
`lipid peroxidaiion
`free-radical
`rer, c/was
`
`.
`
`THE CAROTENOIDS ARE NOT JUST “another
`tiatu-
`of
`group
`and
`special
`ral pigments.”
`They
`are
`substances
`vety
`witil
`remarkable
`properties
`that
`no other
`groups
`of substamices
`and
`of
`possess
`that
`form the
`basis
`their marty,
`varied
`atid
`functions
`actions
`in all kimids of
`livimig organisms.
`Often
`traditionally
`thought
`of as plant
`pigmemits,
`the
`ca-
`rotemioids
`have
`a nluch
`wider
`distribution
`and
`occur
`ex-
`tensively
`also
`in
`animals
`and
`mnicroorganisms.
`Tile
`striking
`natural
`colors
`that
`are
`due
`to carotenoids-e.g.,
`in yellow,
`orange,
`amid red flowers
`amid fruit-are
`familiar
`to all of us,
`but othei’,
`less
`obvious
`roles make
`carote-
`noids
`essential
`components
`in oxygenic
`photosymitlietic
`organisms.
`Without
`carotenoids,
`photosynthesis
`amid all
`life
`in an oxygen
`atmosl)liel’e
`would
`be
`impossible.
`Ca-
`rotenoids
`have
`recemitly
`heemi
`as well
`in tile
`implicated
`prevention
`of or protection
`against
`serious
`huniami health
`disordet’s
`such
`as cancel’
`amid heart
`disease.
`Thus,
`these
`substances
`are clearly
`of major
`inlportance
`in biology.
`obvi-
`The
`natural
`functiomis
`arid actions
`of carotenoids
`prop-
`ously
`are determined
`by the physical
`and chemical
`em’ties of the molecules,
`and
`these
`properties
`are defined
`tue overall
`by
`the molecular
`structure.
`Fit’st,
`molecular
`is
`of
`geometry
`(size,
`shape,
`presence
`functional
`groups)
`and
`vital
`for ensuring
`that
`the carotenoid
`fits
`imito cellular
`location
`amid ot’iemita-
`subcellular
`structures
`in the
`correct
`lion
`to allow it
`to functiomi
`efficiently.
`Secomicl,
`the
`conju-
`gated
`double
`bond
`system (letermimies
`the photochemical
`properties
`and
`chemical
`reactivity
`that
`forni
`the
`basis
`In addition,
`specific
`imiteractions
`these
`functions.
`other molecules
`vicinity
`are
`crucial
`in the
`immediate
`correct
`functioning.
`
`of
`with
`for
`
`Semid corrcsi)onclemio:e ammo!mt’l)nmntmetluests
`
`tim Dr. Britttumm, at: Depart-
`
`Umiiversily of Livt’rpnol,
`mt’nl of Biochemistry,
`L69 3BX. United Kingclomn,
`2Abhreviaiions:
`AIBN,
`2,2’-mzti-bis-isohtmtvmomiitmiIe;
`bis (2.4-dimethiylvuleromiitnile).
`
`AMVN.
`
`2,2’-0mzo-
`
`P.O. Box 147, Lit
`
`t’mpooi
`
`0892-6638/95/0009-i
`
`551/$01.50.
`
`© FASEB
`
`RIMFROST EXHIBIT 1097 page 0001
`
`1551
`
`Downloaded from www.fasebj.org by Michael Chakansky (167.206.200.52) on May 11, 2018. The FASEB Journal Vol. 9, No. 15, pp. 1551-1558.
`
`

`

`to use
`they
`the
`
`its
`
`triv-
`the well-known
`convey
`no itiforma-
`cam’otemioid.
`been
`devised
`unambiguously
`structure.
`the
`stem
`prefixes
`end
`
`A
`that
`in
`
`and
`In essence,
`name
`“caro-
`tllat
`desig-
`groups
`are
`
`iii biological
`especially
`work,
`genel’ally
`even
`though
`ial names
`of
`the
`structure
`tion
`about
`therefore
`scheme
`has
`senlisystematic
`allows
`any carotenoid
`named
`to be
`a way
`that
`defines
`and
`describes
`on
`all
`specific
`names
`are
`based
`tile Greek-letter
`by
`preceded
`tetle,”
`end
`hate
`the
`two
`groups;
`the
`seven
`in Fig.
`lB.
`llustrated
`confusion,
`For
`clarity
`amid to avoid
`group
`prefixes
`for
`a carotene
`is
`Thus,
`for
`example,
`“3-carotene”
`referred
`to as
`p43-carotene,
`etc. Changes
`in hydrogenation
`oxygen-contaimlimig
`substituemits
`used
`and
`standard
`prefixes
`suffixes
`Thus,
`biosynthetic
`precursor
`the
`7,8,11
`,12,7’,8’,1
`1’,12’-octahydm’o-,-carotene,
`ant hi
`is
`,-carotemie-3,3’-d
`iol. Many
`noids
`are
`optically
`active,
`i.e.,
`chiral
`ciiit’ality
`is
`indicated
`by the
`conventional
`The
`IUPAC-IUB
`rules
`are
`given
`publication
`(4)
`in volume
`1A of
`(5).
`rotenoids
`of
`fewer
`Some carotenoidshave
`consisting
`structure
`a
`thami 40 carbon
`by loss of part
`atoms
`dem’ived formally
`and
`compounds
`are
`referred
`to as
`of
`the C40 skeleton.
`These
`atoms
`have
`been
`lost
`from
`apocarotenoids
`when
`carbon
`the ends
`of
`the molecule
`or as norcarotenoids
`when
`carb-
`on atoms
`have
`heemi
`lost
`formally
`fm’om within
`the
`chain.
`
`SERIAL REVIEW
`
`of
`
`objective
`The main
`structures
`and
`properties
`information
`as a basis
`mnay function
`and
`act
`
`article
`this
`of carotenoids
`for understandimig
`in biological
`systems.
`
`is
`
`the
`to describe
`this
`amid to use
`how carotemloids
`
`CAROTENOID STRUCTURES AND
`NOMENCLATURE
`
`have
`
`is
`
`than 600 differemit
`isolated
`been
`carotetioids
`More
`(1, 2). For
`the
`characterized
`fm’om natural
`sources
`and
`of having
`to assimi-
`prospect
`newcomer
`to the
`field,
`the
`late
`such
`a mnass of detailed
`cheniical
`imiformation
`dautititig.
`Fortunately,
`although
`these
`are
`all
`different
`as
`structures,
`for mamiy purps
`cati be considered
`they
`variatiomis
`omi a structural
`of
`imi terms
`oi many
`and,
`the
`chemical
`and
`properties,
`the
`carote-
`basic
`noids
`niay he cotlSidel’e(l
`
`theme
`physical
`as
`a gt’oup.
`
`Basic
`
`structure
`
`are
`
`compounds,
`isoprenoid
`carotenoids
`The
`biosynthe-
`two C20 geranylgeranyl
`of
`linkage
`sized by tail-to-tail
`C10
`prodttces
`the
`parent
`This
`diphiosphate
`molecules.
`the
`imidividual
`variations
`carbon
`skeleton
`fi’om which
`all
`1A, this basic
`are derived.
`structure
`is illustrated
`In Fig.
`by lycopene
`atid ,-carotene;
`the
`carotenoid
`numbering
`1)
`scheme
`is also
`shown.
`skeleton
`can
`be modified
`This
`to
`by cyclization
`at one
`end or both
`ends
`of
`thie molecule
`in
`the
`seven
`different
`end
`groups
`(illustrated
`give
`Fig. 1B), 2) by changes
`amid 3) by
`in hydi’ogenation
`level,
`addition
`of oxygemi-comitai ni ng functional
`groups.
`Carote-
`noids
`that
`contain
`one
`or more
`oxygen
`functions
`are
`known
`as xanthophylls,
`the
`parent
`hydrocarbons
`as
`caro-
`tenes.
`
`been
`
`is
`
`given
`source
`still
`
`names
`trivial
`from which
`tile
`common
`practice,
`
`Nomenclature
`
`Traditionally,
`derived
`usually
`carotenoid
`was
`
`have
`carotenoids
`biological
`from the
`first
`isolated.
`It
`
`A7
`
`18
`
`tO
`
`20
`
`I7JJ3
`
`Lycopene
`
`-carotene
`
`and nunibening scheme
`Figure
`1. A) Basic
`of au acydie
`structure
`B) The
`carotenoid (lycopene)
`an a dicyelic
`carotenoid
`(,J-carotene).
`seven different
`end groups found in natural
`carotenoids,
`
`of
`the
`
`end-
`of both
`use
`the
`(3).
`now recommended
`correctly
`now more
`is
`a-carotene
`as
`,E-carotene,
`level
`the
`presence
`and
`indicated
`by
`are
`in organic
`chemistiy.
`phytoene
`becomes
`amid zeax-
`carote-
`nat ural
`compounds;
`R,S system.
`in full
`an
`IUPAC
`iti
`new series,
`Ca-
`the
`
`ii
`
`and
`
`The polyene
`
`chain
`
`is
`
`of the carote-
`feature
`and characteristic
`striking
`The most
`of
`alternating
`double
`the
`long
`system
`tioid
`structure
`centm’al
`part
`of
`the mole-
`that
`forms
`the
`and
`single
`bonds
`tue
`system
`in which
`cule.
`This
`constitutes
`a
`conjugated
`are
`effectively
`delocalized
`over
`the
`entire
`it-electt’ons
`
`17
`
`16
`
`17
`
`16
`
`2
`
`2><r(R
`
`18
`#{163}35LR
`16
`
`2
`
`4
`
`6
`
`4518
`
`p
`
`C
`
`16
`
`5
`
`18
`
`16
`
`1
`
`CH2R
`
`18
`
`:i
`2L.,,,,J4
`
`K
`
`17
`
`16
`
`17
`
`18
`
`I
`
`17.
`
`18
`
`x
`
`1552
`
`Vol. 9 December 1995
`
`The EASER Journal
`
`RIMFROST EXHIBIT 1097 page 0002
`
`BRITFON
`
`Downloaded from www.fasebj.org by Michael Chakansky (167.206.200.52) on May 11, 2018. The FASEB Journal Vol. 9, No. 15, pp. 1551-1558.
`
`

`

`the
`of
`length
`the
`carotenoids
`shape,
`chemical
`ties.
`
`chain.
`polyene
`a group
`as
`reactivity,
`
`Stereochemistry
`
`feature
`is this
`It
`their
`distinctive
`and
`light-absorbing
`
`gives
`that
`molecular
`proper-
`
`bonds,
`double
`C=C
`around
`isomerism
`of
`Because
`distinctly
`These
`are
`possible.
`ent
`configurations
`are
`isolated
`be
`that
`can
`ferent
`molecular
`structures
`is theoretically
`rotation
`separate
`compounds.
`In addition,
`possible
`about
`any C-C single
`bond
`imithe polyene
`chain,
`so the
`carotenoids
`can,
`in principle,
`adopt
`an enormous
`number
`of shapes
`or conformations.
`
`differ-
`dif-
`as
`
`Configuration:
`
`geometrical
`
`isomers
`
`chain
`
`bond in the polyene
`each double
`In principle,
`of a
`desig-
`can
`exist
`in two
`forms
`(configurations),
`carotenoid
`or cis, depending
`trans
`of substi-
`on the
`disposition
`nated
`a
`tuent
`groups,
`specifically
`those
`that
`constitute
`bond
`continuation
`of the polyene
`chaiti,
`about
`that double
`(Fig.
`(5)
`2A).
`[In current
`chemical
`usage,
`the configiira-
`E or Z.
`tion about
`a double
`bond
`is designated
`In carote-
`Z are
`E and
`trans
`noids
`usually
`equivalent
`and
`cis,
`to
`respectively,
`although
`there
`are
`some
`exceptiomis.]
`This
`gives
`rise
`to a large
`number
`of
`theoi’etically
`possible
`monocis
`and
`polycis
`isomers.
`In
`reality,
`only
`a few of
`these
`geometrical
`isomers
`are encountered
`in nature.
`Tue
`of a cis double
`bond
`creates
`greater
`steric
`hin-
`presence
`drance
`between
`nearby
`hydrogen
`atoms
`and/or
`methyl
`so that
`isomers
`are generally
`less
`stable
`ther-
`groups,
`cis
`modynamically
`than
`the
`form. Most
`carotenoids,
`trans
`the
`therefore,
`occur
`in nature
`pi’edominantly
`or entirely
`in
`that
`all-trans
`form. With
`some
`double
`bonds,
`i.e.,
`those
`C-
`bear
`three
`substituents
`and
`also
`the
`disubstituted
`bond, the
`15,15’
`so that
`double
`steric
`hindrance
`is
`small
`isomers with cis double
`are rela-
`bonds
`in these
`positions
`13-
`tively
`easily
`formed
`and relatively
`stable
`(e.g.,
`9-cis-,
`and
`15-cis-f34-carotenes).
`With
`other
`disttbstituted
`cis-,
`
`SERIAL REVIEW
`
`double
`however,
`bonds,
`jor
`steric
`interference
`drogen
`atom (5)
`sterically
`hindered
`rarely
`encountered
`carotemie.
`
`configuration
`a cis
`a methyl
`between
`Isomers
`(Fig.
`2B).
`are hard
`double
`bonds
`in nature,
`e.g.,
`7-cis-
`
`ill ma-
`t’esults
`a Ily-
`group
`and
`such
`containing
`to form and are
`and
`11-cis-3-
`
`Gonformat
`
`ion
`
`in
`
`a carotenoid
`primiciple,
`Although,
`cart
`cis/trans
`adopt
`a very
`configuration
`the
`in practice
`carotenoid
`will
`shapes,
`lar preferred,
`low-energy
`conformation.
`
`a defined
`with
`large miumber
`exist
`in a particu-
`
`of
`
`form of the con-
`stable
`the most
`chain. By far
`The polyene
`conformatioti.
`extended
`jugated
`polyene
`chain
`is a linear,
`First,
`a comiju-
`for
`this.
`Two major
`factors
`are
`responsible
`when
`the double
`bonds
`gated
`system is greatly
`stabilized
`are
`coplanar.
`Second,
`steric
`himidm’ance is
`smallest
`whemi
`each
`C-C single
`bond
`is
`in
`the
`conformatiomi
`s-trans
`(equivalent
`to a trans
`double-bond
`configuration,
`Fig.
`2C).
`reveal
`X-Ray
`crystallographic
`data
`that
`carotemioids
`are
`essentially
`extended
`linear molecules
`with
`omily a slight
`5-shaped
`distortion
`to relieve
`stet’ic
`tension
`(6).
`
`rota-
`free
`theoretical
`of
`Because
`ring-chain
`The
`junction.
`with cyclic
`bomid in carotenoids
`tion about
`the C-6,7
`single
`end groups,
`in principle
`there
`can be an
`of
`number
`imif’inite
`possible
`angles
`of twisting
`between
`the ring and the main
`polyene
`chain.
`In the n-ring
`carotenoids,
`the C-5,6
`double
`bond is formally
`conjugated
`the polyene
`chaimi, so tilat
`with
`coplanarity
`of
`the ring and chain
`double
`bonds
`should
`be
`and 6-s-
`favored.
`There
`are
`two extreme
`structures,
`6-s-cis
`(Fig.
`that
`allow such
`coplanarity,
`these
`trans
`2D),
`but
`(5).
`would
`generate
`considerable
`steric
`crowding
`It
`is now
`is 6-s-cis,
`but this
`kmlown
`that
`the
`preferred
`cotiformation
`is distorted
`approximately
`40#{176}from planarity
`to relieve
`the C-5 methyl
`substituent
`on
`steric
`interference
`between
`the C-8 hydrogen
`(7). With
`the l’ing
`atom of the chain
`and
`tue E-rimtg,
`bond (C-4,5)isnot in
`the cyclic
`double
`conju-
`
`H\
`
`/R2
`
`IsS
`
`\
`/
`R1
`
`c=c
`
`R2
`
`H
`
`/
`\
`
`H
`\
`
`R(
`
`c==c
`
`/
`
`\
`
`H
`
`\
`
`/
`
`2Rt
`
`C’s
`
`/
`\
`
`R2
`
`C s-cis
`
`c-c,
`
`S - trans
`
`/O==C\
`Rm
`A
`
`H
`
`Irons
`
`B ‘unhindered’
`
`‘hindered’
`
`D 6 - s - cis
`
`6 -s-trans
`
`2. A) cis and trans
`Figure
`C) The s-cis and s-trans
`
`cis double bonds in the pol’ene
`and “unhindered”
`“hindered”
`bonds in cam’otenoids. B) Stenically
`double
`of single bonds in the polyene
`chain. D) The 6-s-cit
`and 6-s-trans
`conformations
`conformatiomis
`of n-ring
`
`chain of carotenokJs.
`carotenoids,
`
`STRUCTURE
`
`AND
`
`PROPERTIES
`
`OF CAROTENOIDS
`
`RIMFROST EXHIBIT 1097 page 0003
`
`1553
`
`Downloaded from www.fasebj.org by Michael Chakansky (167.206.200.52) on May 11, 2018. The FASEB Journal Vol. 9, No. 15, pp. 1551-1558.
`
`

`

`SERIAL REVIEW
`
`so that
`determinant
`
`relief
`
`becomes
`crowding
`of steric
`the preferred
`ring-chain
`
`of
`
`only
`the
`conforma-
`
`gation,
`major
`tion.
`The
`together
`conformatiomi,
`ring-chain
`ring
`itself-normally
`a chair
`or
`tile
`of
`determnined
`the
`presence
`mation
`by
`of
`gm’oups-establish
`effective
`bulk
`
`the
`
`shape
`with
`confor-
`half-chair
`of
`functional
`the end group.
`
`the
`
`PROPERTIES
`
`General
`
`properties:
`
`size,
`
`shape,
`
`solubihity
`
`in
`
`af-
`
`hiydrophobic
`extremely
`are
`a group
`as
`cat’otenoids
`The
`are
`or
`no solubility
`in water.
`They
`little
`molecules
`with
`the
`restricted
`to hydrophobic
`areas
`to be
`thus
`expected
`in
`the
`inner
`core
`of membranes,
`except
`cell,
`such
`as
`wheti
`associatiomi
`with
`protein
`allows
`theni
`access
`to an aqueous
`emivironment.
`(See
`section
`on Properties
`atid Molecular
`Interactions
`of Carotenoids
`Polar
`vivo.)
`functional
`in
`groups
`obviously
`alter
`tile
`of carotenoids
`and
`polarity
`fect
`their
`interactions
`with
`other molecules.
`ex-
`are
`The
`overall
`size
`and
`shape
`of
`the mnolecule
`tremely
`important
`imi relation
`to the
`properties
`of a carote-
`noid
`and,
`hence,
`to functiomi.
`All
`colored
`carotenoids
`the
`configuration
`all-trans
`au
`have
`extended
`conjugated
`Tim
`are
`double-bond
`and
`linear,
`rigid molecules.
`system
`cis-isomers,
`however,
`are mio longet’
`simple
`linear
`mole-
`cules.
`Their
`overall
`shape
`differs
`substantially
`from that
`of
`the
`all-trans
`form,
`so their
`ability
`to fit
`itito
`subcellular
`structures
`may
`be greatly
`altered.
`temidetmy
`of cis-iso-
`The
`niers
`to crystallize
`or
`aggregate
`usually
`much
`less;
`is
`tllerefore
`cis-isomers
`may
`be more
`readily
`solubilized,
`ab-
`sorbed,
`amid transpom’ted
`than
`their
`counterparts.
`all-trans
`The
`shape
`and
`size
`of
`the
`emid groups
`are
`also
`impot’-
`such
`as lycopene
`are
`es-
`tant
`factors.
`Acychic
`cat’otemioidls
`sentially
`long,
`hineam’ mnolecules with flexible
`end
`groups.
`Cychizatioti
`the molecule
`the overall length of
`shortens
`and
`increases
`the
`effective
`bulk
`of
`the
`end
`groups
`and
`the space
`they occupy.
`The
`effective
`bulk depends
`on the
`preferred
`conformatiomi,
`as
`detertnined
`by steric
`factors
`and
`the
`presence
`of
`subslituent
`groups,
`and
`can
`be
`al-
`tered
`sigmiificantly
`by apparently
`small
`structural
`changes
`such
`as epoxidation-deepoxidatiomi.
`
`Light
`
`absorption
`
`and photochemical
`
`properties
`
`by an
`molecule
`orgatlic
`energy
`light
`of
`absorption
`The
`that molecule.
`excited
`produces
`a llighler-eflergy
`of
`state
`relevamit
`transition
`is a
`the
`case
`of carotenoids,
`In
`the
`otie of the botiditig
`IL-elections
`transition,in which
`y*
`the
`of
`comijugated
`double-bomid
`systeni
`is pronioted
`to a
`The
`previously
`unoccupied
`antibondiiig
`orbital.
`it-
`ic
`state
`and
`excited
`is
`the
`electromis
`are
`highly
`delocalized
`of comparatively
`low energy,
`the
`energy
`required
`to
`so
`is
`bring
`about
`the
`transition
`relatively
`small
`amid corre-
`visible
`sponds
`to light
`the
`region
`the wavelength
`in
`range
`of 400-500
`nmii. Carotenoids
`are
`therefore
`intensely
`The
`colored
`yellow,
`orange,
`or
`red.
`relationship
`betweemi
`chromophiore atidlight-absorptionproperties,widely used
`
`in
`
`of carotenoids,
`
`is developed
`
`more
`
`idetitification
`the
`in
`fully elsewhere
`(8).
`of carotenoids.
`function
`sole
`tile
`But
`coloration
`is not
`properties
`that
`form
`They
`have
`distinctive
`photochemical
`functions
`(9). The
`the
`basis
`of other,
`even more
`impol’tant
`lies
`in the iispo-
`origin
`of these
`photocheniical
`Properties
`states
`(both
`singlet
`sition
`of
`the
`low-lying
`excited!
`energy
`characteristic
`strong
`and
`triplet)
`of
`the
`carotenoids.
`The
`absorption
`of
`light
`in the visible
`region
`is now attributed
`So
`a stm’onglyallowed transitionfrom the ground
`state
`to
`to the
`secomid
`singlet
`excited
`state,
`S2 (1’Bu).
`The
`energy
`levels
`of
`this
`excited
`state,
`and
`of
`the
`somewhat
`lower
`first
`excited
`state
`Sj
`(l’Ag)
`that
`can
`be
`formed
`from it by
`ititernal
`conversion,
`lie close
`to but
`above
`those
`of chlo-
`rophiyll,so that singlet-singletenergy transfercan take
`place
`from excited
`carotenoid
`to generate
`the excited
`sin-
`glet
`whichi
`is active
`in photosyn-
`state
`S1 of chlorophyll,
`(9).
`thesis
`state
`triplet
`carotenoid
`the
`of
`formation
`Direct
`states
`sitiglet
`excited
`frotn the
`via
`singlet-triplet
`S2 or Si
`formation
`by en-
`imitersystem crossitig
`is not
`favored.
`Its
`ergy
`transfer
`from other
`triplet-state
`molecules
`acting
`as
`photosetisitizers
`can
`be
`very
`efficient,
`however,
`provided
`the cat’otenoidcontains more than seven conjugated dou-
`ble botlds,
`because
`the
`carotenoid
`triplet-state
`energy
`is
`low (9).Transfer of energy from triplet-statechlorophyll
`or other porphyrimis
`to carotenoids
`occurs
`much more
`readhilythamithe alternative
`energy
`transfer
`to oxygen
`to
`form the
`hiighly
`reactive
`destructive
`singlet
`oxygen
`and
`102. Carotemloids
`can
`also
`accept
`excitation
`energy
`from
`should
`be fornied.
`The
`triplet-state
`carotenoid
`102
`if any
`
`(Ii)
`
`other
`to generate
`is unable
`it
`that
`low energy
`is of such
`it dissipates
`its
`excitation
`aild
`species
`by energy
`transfer
`surroundings.
`allows
`energy
`harmlessly
`to its
`This
`carotetie
`to pt’otect
`photosynthietic
`reaction-center
`plexes
`agaimist
`damage
`thiat would
`be
`caused
`combination
`of light
`and oxygen
`(9) amid to provide
`fective
`treatmetit
`for
`humaii
`patients
`suffering
`etytht’opoietic
`protoporphyria,
`a condition
`in which
`porphiyrimis
`accumulate
`in the
`skin
`and
`sensitize
`the
`mation
`of
`‘02
`(10).
`or
`singlet
`either
`imivolving
`transfer
`For
`efficient
`energy
`in
`l)e held
`must
`concerned
`triplet
`states,
`tile molecules
`by specific
`close
`proximity
`and
`in tile correct
`orientation
`for example,
`interactions
`other
`niolecules
`such
`as,
`withl
`(9) (see
`proteins
`section
`on Pioperties
`amid Molecular
`In-
`of Carotenoids
`
`tem’aclions
`
`in vivo).
`
`com-
`by a
`ef-
`an
`from
`free
`for-
`
`Cheniical
`
`properties
`
`amid of
`radicals
`of cat’otemioid
`chemistt’y
`fundaniemital
`The
`peroxy
`agents,
`with oxidizing
`the reactions
`of carotenoids
`the proposed
`ac-
`for evaluating
`ra(hicals,
`etc.,
`is important
`it
`is not well
`un-
`tions
`of carotenoids
`as
`antioxidants,
`but
`here
`dherstood. The
`strategy
`adopted
`is not
`to survey
`the
`literature
`that
`deals
`with
`carotenoids
`as
`amltioxidants,
`but
`to consider
`the
`pt’operties
`of
`the
`carotenoicis
`amid their
`t’adicals
`and
`the
`chemistiy
`of
`their
`reactions
`with
`oxidiz-
`
`1554
`
`Vol. 9 Deceml,er
`
`1995
`
`The FASEB journal
`
`RIMFROST EXHIBIT 1097 page 0004
`
`BRITON
`
`Downloaded from www.fasebj.org by Michael Chakansky (167.206.200.52) on May 11, 2018. The FASEB Journal Vol. 9, No. 15, pp. 1551-1558.
`
`

`

`ing agents
`or other
`
`a basis
`as
`chemical
`role
`
`whether
`assessing
`for
`in vivo
`is feasible.
`
`an antioxidant
`
`Carotenoid
`
`radicals
`
`reac-
`free-radical
`are
`oxidations
`important
`the
`of
`Many
`and
`properties
`of the generation
`so a consideration
`tions,
`radicals
`de-
`and of carbon-centred
`of carotenoid
`radicals
`species
`is
`by addition
`of other
`rived
`from carotenoids
`relevant
`(11). The
`carotenoid
`radicals
`are very short-lived
`species.
`Some
`information
`has been
`obtained
`about
`thiem
`by the
`application
`of
`radiation
`techniques,
`particularly
`In
`pulse
`radiolysis.
`primiciple,
`carotenoid
`radicals
`can
`generated
`in different
`ways.
`
`be
`
`Oxidation.
`remove
`one
`the radical
`
`Oxidizing
`electron
`cation.
`
`cati
`radicals with high redox potential
`from the
`carotenoid
`molecule
`to give
`
`CAR-e
`
`e.g.,
`
`CAR+R:
`
`-+
`
`-
`
`cAR:
`
`CAR:
`
`+
`
`R
`
`Reduction.
`molecule
`
`The
`would
`
`aclditiomi
`give
`the
`
`of one
`radical
`
`electron
`anion.
`
`to the
`
`cat’otenoid
`
`CAR+e
`
`-* CAR.
`
`abstraction.
`Hydrogen
`H from a sattirated
`polyene
`chain
`can
`radical
`by homolytic
`if
`
`The
`carbon
`generate
`cleavage
`
`of a hiydrogemi atom
`abstraction
`atom in a position
`allylic
`to the
`a resonance-stabilized
`neutm’al
`of a C-H bond.
`instance,
`
`For
`
`CAR=X-H,
`
`thenX-H+R--4X-I-RH
`
`as a per-
`such
`species
`of a radical
`addition
`The
`Addition.
`HO’ to the
`ROO
`radical
`hydroxyl
`or
`radical
`oxy
`tile
`polyene chain could gemieratea cam’otenoid-aciductradical,
`e.g.,
`
`CAR + ROO-CAR
`
`- OOR
`
`carotenoid
`the
`delocalized
`This
`has
`reactions,
`the molecule.
`of
`detected
`by
`their
`intense
`absorption
`
`In
`highly
`phore.
`sequent
`parts
`be
`with
`12).
`
`electromi
`unpaired
`the
`t’adicals,
`cht’omo-
`conjugated
`polyene
`over
`the
`allows
`sul)-
`effect
`also
`a stabilizing
`e.g.,
`additions,
`place
`at many
`The
`cation
`t’adicals
`can
`charactei’istic
`properties,
`in the
`regiomi
`(11,
`
`is
`
`and
`to take
`atid
`anion
`spectral
`infrared
`
`near
`
`Chemical
`
`reactions:
`
`oxidation
`
`imi
`important
`are
`groups
`end
`of carotenoid
`reactions
`The
`dei’i-
`in characterization,
`classical
`for example,
`chemistry,
`are
`reactions,
`however,
`vatization,
`and
`synthesis.
`Such
`in relatiomi
`to function.
`gemierally
`not of great
`significance
`tue most
`the mnolecule
`is
`the
`Here
`important
`pam’t of
`polyene
`chain.
`This
`is a hiighly
`reactive,
`electron-rich
`
`sus-
`are
`broken
`be
`pt’esence
`are
`usually
`and
`other
`in vivo,
`how-
`to oxidative
`species
`imidication
`of
`color
`
`or
`
`re-
`is
`
`any
`
`SERIAL REVIEW
`
`by electrophiilic
`of carotemtoids
`feature
`of
`
`re-
`to-
`the
`
`of
`
`to attack
`susceptible
`is
`system that
`the
`imistahility
`agents,
`is responsible
`for
`tile
`important
`ward
`oxidation,
`is
`and
`tnolecule
`in relation
`to free-radical
`chemistry.
`state,
`Pure
`carotenoids,
`even
`in the
`crystalline
`ceptible
`after
`isolation
`to oxidation
`and may
`down
`rapidly
`if
`samples
`are
`stored
`in
`tile
`even
`traces
`of oxygen.
`In vivo,
`tile
`carotenoids
`stabilized
`to a considerable
`degree
`by proteins
`molecules
`in their
`immediate
`vicinity.
`Even
`ever,
`the
`carotenoids
`are
`still
`susceptible
`if
`damage
`they
`become
`exposed
`to oxidizing
`free
`radicals
`that may
`be generated.
`Tile
`usual
`of
`carotenoid
`breakdown
`is
`bleaching,
`i.e.,
`loss
`due
`to breaking
`of the
`chromophore.
`Oxidative
`degradation
`in the
`years
`for many
`used
`was
`of carote-
`elucidation
`classical
`chemistry
`that
`led to the
`noid
`structures
`(13).
`Comitt’olled
`chemical
`reactions
`were
`used to break variouscarbon-carbon double bonds imitue
`polyene
`chaiti
`to generate
`apocarotenals
`and
`apocaro-
`tenones
`as well
`as
`small
`fragments
`aI’isimig from complete
`breakdown.
`by free-radical
`is also caused
`breakdowmi
`Oxidhative
`bleaching
`by hydt’oxyl
`radicais
`actions;
`indeed,
`rapid
`this
`area
`hias concen-
`iti
`work
`well
`known
`(14).
`Recent
`trated
`on the
`in
`with
`pet’oxy
`t’adicals
`generated
`reactions
`by the CCI;100
`by pulse radiolysis.
`e.g.,
`some
`cases
`radical
`(15),
`but mostly
`by use of so-called
`azo-initiators
`as 2,2’-azo-bis-isohutyronitrile
`(AIBN)
`and 2,2’-azo-
`such
`bis(2,4-dimethylvaleronitrile)
`(AMVN).
`Comitrolled
`diet’-
`these
`ma!
`decomposition
`of
`substamices
`generates
`free
`the
`radicals
`thiat,
`presence
`of oxygen,
`give
`rise
`to the
`iti
`cort’esponchimig
`peroxy
`radicals
`(16).
`These
`imi turn
`react
`with the carotenoids. A wide
`variety
`of products
`have
`seem to be apocaro-
`been
`detected
`in these
`studies.
`Most
`letigthis
`pro-
`tenals
`ot’ apocarotemlones
`of various
`chain
`(huced
`by
`cleavage
`of
`(hoUble
`bond
`the
`pohyene
`iii
`foumid (17, 18).
`chaiml;
`epoxides
`are
`also
`commonly
`Sitiiilar
`chemical
`reactions
`occur
`also
`betweemi
`cam’ote-
`noids
`and
`singlet
`oxygen,
`andh agaimi gemierate
`apocam’o-
`temials
`and
`apocat’otenomles
`as
`the major
`I)t’o(1u(ts.
`The
`niechiamiism may
`i)e diffem’ent,
`howevem’, and may
`involve
`the
`addition
`of
`‘02
`to a double
`bond
`to form a labile
`di-
`oxetamie, which
`is then
`cleaved
`to give
`the
`cort’espomidling
`cat’bonyl
`prodtmcts
`(18).
`with oxi-
`of cat’otenoids
`In all
`the work on tile reactiomis
`products
`hiowever,
`dizing
`amid free-radical
`reagents,
`tile
`smaller
`only in much
`that
`are seen
`are usually
`detectable
`amounts
`than
`the
`amount
`of carotenoid
`that
`is destroyed.
`Also,
`the substances
`that
`cart be isolated
`are not
`the pri-
`maiy
`products
`of the reactions.
`The primary
`products
`will
`be generated
`extremely
`rapidly
`and
`have
`only
`a very
`shiort
`lifetime
`before
`they
`undergo
`further
`reactions
`that
`eventually
`lead
`to the
`formation
`of stable
`products
`that
`can
`be
`isolated.
`Neverthieless,
`attempts
`have
`been made
`to imifer what
`the primary
`reactiomis may be and
`to deduce
`the subsequent
`course
`of the reactions
`from the identities
`of these
`stable
`products.
`
`STRUCTURE AND PROPERTIES OF CAROTENOIDS
`
`RIMFROST EXHIBIT 1097 page 0005
`
`1555
`
`Downloaded from www.fasebj.org by Michael Chakansky (167.206.200.52) on May 11, 2018. The FASEB Journal Vol. 9, No. 15, pp. 1551-1558.
`
`

`

`SERIAL REVIEW
`
`proposed
`have
`(19)
`Ingold
`an(l
`thlat whien
`Burton
`gener-
`radicals
`reacts with
`peroxy
`in solutiomi,
`carotene,
`ated
`via AIBN,
`place
`to form a
`addhition
`takes
`a direct
`resonance-stabilized,
`carbon-centred
`radical.
`This
`could
`then react with a further
`peroxy
`to form a tionradi-
`cal product
`(20),
`e.g.,
`
`radical
`
`R00
`
`+CAR
`
`-s ROO-CAR’
`
`ROO-CAR
`
`+ROO
`
`-s ROO-CAR-OOR
`
`this
`coticentratiotis,
`low oxygen
`relatively
`At
`carotenoid
`peroxy
`radicals
`and
`the
`consunle
`would
`act as a chiain-breakimig
`amitioxidamit. Alternative
`are possible,however, especiallyat higher
`cemltratiotis
`when
`a carotenoid
`radical
`could
`oxygemi
`to gemierate
`a cai’otemioid peroxy
`radical,
`
`process
`wouldh
`pathways
`oxygemi con-
`react with
`CAR-00
`
`CAR+O,
`
`-sCAR-00
`
`Thus
`eroxy
`oxidation
`ing damage
`
`an
`
`autooxidation
`
`is
`act
`could
`radical
`of unsatui’ated
`(18),
`e.g.,
`
`process
`
`and
`per-
`promoting
`as a prooxidant,
`lipid
`(LH)
`and hence
`exacei’bat-
`
`tile
`
`carotetioid
`
`CAR-00
`
`+LH-*CAR-OOH+L
`
`L0,
`
`-* L-OO’
`
`react
`carotenoids
`All
`carotenoids.
`d/j’erent
`of
`Reactivity
`the
`agents
`atid free radicals,
`though
`rapidly with oxidizing
`the
`lemigth of
`the
`polyene
`cht’onio-
`reactivity
`depends
`omi
`phuore and,
`to some
`extent,
`on the nature
`of the end groups.
`The
`it-electrons
`of
`the polyene
`chain
`ate delocalized,
`aI-
`though
`calculations
`show thiat
`the
`electron
`density
`is not
`uniform but
`is greater
`at or toward
`the ends
`of the chromo-
`phiore.
`These
`are
`therefore
`likely
`to be
`the
`preferred
`sites
`for reactions
`with electrophilic
`or free-radical
`species.
`This
`is seen
`imireactions
`with epoxidizing
`agents
`that prefereti-
`tially
`attack
`the terminal
`double
`bond and in the preferred
`oxidative
`chain
`cleavage
`at
`the C-7,8
`position.
`Differences
`in reactivity
`can be explained
`by differences
`in electronic
`S. W. M. Lee, R. J.
`density
`profiles
`(21; A. A. Woodall,
`Weesie, M. J. Jackson,
`amid C. Britton,
`unpublished
`re-
`sults).
`4-Carotemie
`and
`its 3,3’-diol
`(zeaxanthin),
`which
`have
`the
`same
`chromophore,
`have
`similar
`electron
`very
`density
`profiles. With
`canthaxanthimu
`and
`astaxamithin,
`how-
`ever, tueelectron-withdrawing
`properties
`of the conjugated
`keto groups
`at C-4 and C-4’
`cause
`substantial
`changes
`the
`electron
`density
`along
`the
`polyene
`chain,
`especially
`near
`to the
`end
`groups.
`Astaxanthin
`and
`canthaxamithin
`generally
`react more slowly with oxidizing
`agents
`than does
`,-carotene,
`and
`the preferred
`sites
`of
`reactions
`such
`as
`epoxidation
`are different.
`do not
`Substituemit
`groups
`that
`mophore
`can also have
`a significant
`
`comitribute
`influence
`
`chro-
`to the
`on the rate
`
`in
`
`of
`
`of reaction
`rates
`The
`reactions.
`of oxidation
`and course
`and
`,-carotene
`with
`peroxy
`zeaxanthiin,
`3,3’-diol,
`its
`are very similar,
`but
`azoinitiators,
`generated
`via
`radicals
`the
`4,4’-diol,
`isozeaxanthin,
`althioughi
`it has
`the
`same
`chiromophore,
`reacts
`slowly;
`the 4,4’-diketoties,
`can-
`more
`thaxanthin
`and
`astaxamithiin,
`react more
`slowly
`still. The
`differences
`imi reactivity
`are
`attributed
`to the presence
`of
`the hydroxy
`or keto substituents
`in the allylic C-4 and C-
`4’ positions,
`preventing
`hiydm’ogen
`abstraction
`ft’om these
`positiomis
`to give
`a resonance-stabilized
`neutral
`radical
`(21; Woodahl
`atid Lee et al., utipublished
`results,
`22).
`
`Carotenoids
`
`as antioxidants
`
`can-
`includimig
`diseases,
`human
`serious
`Matiy of the most
`stage
`involve
`oxidation
`some
`at
`cer
`and
`heart
`disease,
`free
`as HO and
`radicals
`such
`by
`processes
`mediated
`ROO
`(22).To be
`an effective
`antioxidant,
`a molecule
`would! have
`to remove
`these
`radicals
`such
`as a carotenoid
`from the
`system either
`by m’eacting with
`them to yield
`harmless
`products
`or by disruptimig
`free-radical
`chain
`re-
`actions.
`It has been
`shown
`that
`carotemioids
`cati he effec-
`tive
`antioxidants
`in organic
`solution
`under
`defined
`conditions,
`especially
`at
`comparatively
`low oxygen
`con-
`centrations
`(19).
`Several
`competing
`reactions
`are
`possi-
`ble,
`however,
`especially
`complex
`systems.
`Some
`of
`in
`these
`be antioxidant
`reactions,
`but others may lead
`may
`to a prooxidamit
`the carotetioid
`(18).
`action
`of
`of
`The
`situation
`in vivo is not clear. Thie concentrations
`carotenoids
`in mammalian
`tissues
`generally
`are much
`lower
`than
`those
`used
`to demonstrate
`antioxidant
`behav-
`iot’ in model
`systems.
`To act as an antioxidant
`the
`in vivo,
`carotenoid
`would
`need
`to be imucorporated
`into the tissues
`in the
`correct
`location
`and
`at a suitable
`concentration
`relative
`to the oxidizing
`agent
`and
`the molecule
`that
`is to
`be protected.
`It
`is by no means
`certain
`
`th#{236}atthese
`condi-
`tions
`can be fulfilled.
`
`PROPERTIES AND MOLECULAR
`INTERACTIONS
`OF CAROTENOIDS
`
`IN VIVO
`
`General
`
`considerations
`
`to
`
`about
`in
`
`and
`
`proper-
`chemical
`the physical
`is known
`Much
`In
`vivo,
`solutions.
`simple
`organic
`carotenoids
`of
`ties
`complex
`are
`part
`of
`a much
`niore
`carotenoids
`however,
`cell-and
`are
`close
`proximity
`living
`system-the
`in
`such
`as proteimis
`lipids,
`frequently
`other
`components
`and
`ordered
`structures
`as metnbranes.
`organized
`and
`such
`in
`The
`carotenoid
`must
`be able
`to fit
`into this
`complex
`sys-
`the correct
`location
`and orientation.
`tem in
`The overall
`of a carote-
`shape,
`size,
`and hydrophohicity
`muoid are obviously major
`features
`that dietermine
`the abil-
`ity of a carotenoid
`to fit
`into
`subcellular
`structures.
`The
`structural
`details
`that
`characterize
`the
`individual
`carote-
`noid
`then
`define
`the precise
`oriemitation
`that
`carotenoids
`cart adopt
`as well
`as the interactions
`of the molecule
`with
`its
`surroundings.
`Polar
`fumictional
`groups
`provide
`a focus
`
`1556
`
`Vol.9 December
`
`1995
`
`The FASEBjournal
`
`RIMFROST EXHIBIT 1097 page 0006
`
`BRITFON
`
`Downloaded from www.fasebj.org by Michael Chakansky (167.206.200.52) on May 11, 2018. The FASEB Journal Vol. 9, No. 15, pp. 1551-1558.
`
`

`

`to al-
`in ordler
`polar molecules
`with more
`imuteractions
`for
`in an aqueous
`to pat’ticipate
`imuevents
`low the
`carotenoid
`or at an interface
`or membrane.
`subcellular
`medium
`Interactions
`between
`carotenoid
`molecules
`thienuselves
`can
`also
`hiave
`a significatit
`effect
`on properties.
`Beimig
`highly
`hydrophobic,
`carotenoids
`show a strong
`temidency
`to aggregate
`and
`crystallize
`in aqueous
`media.
`The
`accu-
`is
`mulation
`of carotenoids
`as micm’ociystalline
`aggregates
`ly-
`common
`imi the
`chromoplasts
`of higher
`plants
`(e.g.,
`copene
`in tomato)
`(23). Aggregation
`changes
`the
`physical
`properties
`of carotenoids,-lighit
`absorptioti
`and
`chemical
`well
`reactivity,
`for
`example-as
`as
`their
`effective
`size
`amid
`ease
`thereby
`ease
`of solubilization,
`affecting
`their
`of ab-
`sorption
`and bioavailability
`in animals
`amid thieir ability
`to
`enter
`and functiomi
`in subcellular
`structures.
`
`Molecular
`
`interactions
`
`Carotenoids
`
`in membranes
`
`are
`
`The physical
`are
`of a cat’otetioid
`prop