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Iridoids in Hydrangeaceae

Gousiadou, Chryssoula; Li, Hong-Qing; Gotfredsen, Charlotte Held; Jensen, Søren Rosendal

Published in:Biochemical Systematics and Ecology

Link to article, DOI:10.1016/j.bse.2015.12.002

Publication date:2016

Document VersionPeer reviewed version

Link back to DTU Orbit

Citation (APA):Gousiadou, C., Li, H-Q., Gotfredsen, C. H., & Jensen, S. R. (2016). Iridoids in Hydrangeaceae. BiochemicalSystematics and Ecology, 64, 122-130. https://doi.org/10.1016/j.bse.2015.12.002

1

Iridoids in Hydrangeaceae

Chrysoula Gousiadoua, Hong-Qing Li

b, Charlotte Gotfredsen

a, Søren Rosendal Jensen

a,*

aDepartment of Chemistry, Technical University of Denmark, DK-2800, Lyngby, Denmark

bSchool of Life Sciences, East China Normal University, Shanghai, China

Abstract

* Corresponding author. Tel.: +45-45252103; fax: +45-45933968.

E-mail address: srj@kemi.dtu.dk (S.R. Jensen).

2

The content of glycosides in Kirengeshoma palmata and Jamesia americana

(Hydrangeaceae) have been investigated. The former contains loganin and

secoiridoids, including the alkaloid demethylalangiside. The latter contains no

iridoids, but the known glucosides arbutin, picein and prunasin. In order to futher

investigate the chemotaxonomy of the family Hydrangeaceae, the distribution of the

iridoid and secoiridoid glucosides as well as the known biosynthetic pathways to these

compounds have been reviewed. However, only a few genera of the family has been

investigated. Loganin, secologanin, and derivatives of these are common. The genus

Deutzia is characteristic in containing more structurally simple iridoids in which C-10

has been lost during biosynthesis. Such compounds have so far only been reported

from the genus Mentzelia (Loasaceae). The taxonomic relationships between

Hydrangeaceae and the closely related Cornaceae and Loasaceae is discussed and

found to agree well with recent DNA sequence results.

Keywords:

Kirengeshoma

Jamesia

Hydrangeaceae

Iridoid glycosides

Chemotaxonomy

3

1. Introduction

de Jussieu (1789) originally placed Hydrangeaceae in Saxifragaceae and this

association was followed by most taxonomists (Bentham and Hooker, 1862-83;

Engler, 1928; Takhatajan, 1969; 1980; Cronquist, 1988). Dahlgren (1975; 1980;

1989), who put a great weight on embryology was impressed by the correlation with

the occurrence of iridoid compounds, and he was one of the first to place the family in

his Cornales. Thorne (1992) and Hufford (1992) followed this concept, and with the

advent of DNA sequencing techniques (Downie and Palmer, 1992; Hufford et al.,

2001; Albach et al., 2001) Loasaceae was also placed in Cornales. The relationships

between the genera of Hydrangeaceae has primarily been analyzed by Hufford (1997;

Hufford et al., 2001). The DNA sequencing phylogenetic relationships are depicted in

Fig. 1.

Only the genera Hydrangea and Deutzia appears to have been much investigated

chemically, probably due the common use of these two genera as garden ornamentals.

The family consists of 17 genera in the two subfamilies (Hufford et al., 2001):

Hydrangeoideae, include tribe Hydrangeeae (Hydrangea, Platycrater, Decumaria,

Pileostegia, Schizophragma, Dichroa, Broussaisia, Deinanthe, Cardiandra) and

tribes Philadelpheae (Philadelphus, Carpenteria, Deutzia, Kirengeshoma, Whipplea,

Fendlerella), and Jamesioideae (Fendlera, Jamesia). In order to extend these studies

we have investigated a member of each of the last two tribes, namely Kirengeshoma

palmata Yatabe and Jamesia americana Torr. & A. Gray .

2. Materials and Methods

2.1 Plant material

Fresh material of Kirengeshoma palmata from two different plants (IOK 8-1999 and

IOK 1-2010) and Jamesia americana (IOK 13-2003) was provided by the staff of the

Botanical Garden of The University of Copenhagen. The vouchers were authenticated

by one of us (HQL) and deposited in the herbarium of East China Normal University

(HSNU).

2.2. General

1H,

13C spectra were recorded Varian Mercury-300 MHz or a Varian Unity plus 500

MHz instrument in D2O or CD3OD using the solvent peak as the internal standard.

The isolated compounds were identified by their 1H and

13C NMR spectra by

comparison with spectra of known standards. Preparative HPLC was performed on a

Merck Lobar RP-18 column size B or C.

2.3. Extraction and isolation

2.3.1 Kirengeshoma palmata

a) Fresh, aerial parts collected in June (65 g) were blended with EtOH (300 ml),

filtered and taken to dryness. Partitioning in H2O-Et2O gave from the aq. phase after

drying 2.5 g which was chromatographed on a C column to give in order of elution:

chlorogenic acid (5, 250mg); salidroside (80 mg); 6--hydroxysweroside (3, 22 mg);

sweroside (2, 740 mg); loganin (1, 80 mg).

b) Fresh, frostbitten aerial parts collected in October (58 g) were cut into small pieces,

blended with EtOH (250 ml), boiled for 10 min and left to extract overnight. The

extract was filtered, dried (3.05 g) and partitioned in H2O-Et2O (2:5). The aq. phase

4

was collected, dried (1.70g) and subsequently subjected to preparative

chromatography. The initial solvent used was H2O, then mixtures of H2O-MeOH of

decreasing polarity, and finally MeOH. The following compounds were obtained in

order of elution: chlorogenic acid (5, 120mg); 6--hydroxysweroside (3, 20 mg);

sweroside (2, 70 mg); loganin (1, 80 mg) and fraction A (50 mg) was obtained.

Fraction A was further purified using the solvent mixture (2:1) to yield

demethylalangiside (4, 10 mg).

2.3.2 Jamesia americana

Frozen aerial parts (23 g) were blended with EtOH (150 ml). After filtering, the

extract was taken to dryness and partitioned in H2O-Et2O. The concentrated aq. phase

(1.50 g) was chromatographed as above to give: sugars (mainly glucose; 310 mg);

arbutin (6; 30 mg); picein (7; 35 mg) and prunasin (8; 150 mg).

2.3.3 Perspective and outline

In order to extend the results obtained from the two plants we have undertaken to

make a review of the iridoids reported from the Hydrangeaceae including the reported

data on the biosynthesis of the compounds found in the family. Furthermore, we have

discussed the distribution of relevant compounds in relation to the phylogenetic

results shown in the cladogram (Fig. 1).

3. Results and Discussion

The aqueous extract of the aerial parts of K. palmata after chromatography on

preparative reverse phase gave loganin (1) and three secoiridoids, namely sweroside

(2), 6-β-hydroxysweroside (3) (Rodríguez et al., 2002) and demethylalangiside (4)

(Itoh et al., 2001) as well as chlorogenic acid (5).

J. americana has been investigated by Plouvier (1959) who discovered the presence

of a cyanogenic glycoside. In the present work, we have isolated the compounds

Arbutin (6), picein (7) (Johansen et al., 2007) and prunasin (8) (Hübel et al,. 1981),

the latter is most likely the cyanogenic compound detected by Plouvier. No iridoids

were found.

The compounds isolated were identified by comparison with spectra of authentic

compounds or published data.

OH

OH

OGlc

N O

4 Demethyl- alangiside

O

OGlc

O O

OH

3 6-Hydroxysweroside

COOH

OH

O

OH

OH

O

OH

OH

5 Chlorogenic acid

O

GlcO

7 Picein

GlcO

OH

6 Arbutin

OGlc

CNH

8 Prunasin

O

OGlc

O O

2 Sweroside

O

OGlc

OH

COOMe

1 Loganin

5

3.1 Biosynthesis

3.1.1 Secoiridoids

The iridoids are of terpenoid origin and their biosynthesis (Fig. 2) has been well

investigated (Inouye et al., 1977a, Inouye and Uesato, 1986; Jensen, 1991, 1992),

although new information about the early steps have recently been discovered (Salim

et al., 2014; Miettinen et al., 2014).

Fig. 2. Biosynthesis of secologanin.

Thus, it has been shown that these compounds are not of mevalonoid origin as first

believed, but that they arise by the recently discovered triose phosphate/pyruvate

pathway via 1-deoxy-D-xylulose in Mentha (Eisenreich et al., 1997) and in Swertia

(Wang et al., 2001) in the case of geraniol. Using cell-free extracts from Lonicera

japonica Thunb. and Hydrangea macrophylla (Thunb.) Ser., it has furthermore been

shown that the initial glucosylation in the pathway take place in the formation of

deoxyloganic acid (11) (Yamamoto et al., 2002). Secologanin (14) has also been

shown to derive from the triose phosphate/pyruvate pathway in Catharanthus roseus

(L.) G. Don cell-cultures (Contin et al., 1998; Miettinen et al., 2014).

3.1.2 Ipecac alkaloids

A group of tetrahydroisoquinoline alkaloids of limited distribution are derived from

secologanin (14). This has been shown in Cephaelis ipecacuanha (Brot.) A. Rich.

O

OH

O

OH

CHO

O

OGlc

COOH

9 Iridodial 10 Iridotrial

11 Deoxyloganic acid

O

OGlc

OH

COOMe

O

OGlc

CHO COOMe

1 Loganin

14 Secologanin

tetrahydro- isoquinoline and complex indole alkaloids

CH3

O

OH H

OH

CH2OH

OH

Geraniol1-Deoxy-D-xylulose

O

OGlc

COOH

OH

12 Loganic acid

O

OGlc

OOH O

13 Secologanic acid

O

OGlc

O O

2 Sweroside

6

(Rubiaceae) by Battersby and Gregory (1968) where labelled loganin (1) was

incorporated in ipecoside (15) which is likely to be the precursor of the ipecac

alkaloids.

Fig. 3. Biosynthesis of ipecac alkaloids.

3.1.3 Deutzia iridoids

The iridoid glucosides found in Deutzia species are peculiar since they lack the C-10

carbon atom, a feature rarely seen in the compounds from other plants. The

biosynthesis (Inouye et al., 1977b, Uesato et al, 1986) is different from that above

(Fig. 4) since glucosylation apparently takes place earlier, namely at the iridodial

stage. Thus, it has been shown by feeding deuterium labelled precursors (Frederiksen

et al., 1999) to proceed from iridodial glucoside (9a) via decapetaloside (16) to the

compounds present in the plants, deutzioside (18) and scabroside (19). The compound

loasaside (17) has not been tested as an intermediate, but seems the logical step prior

to 18 and 19.

Fig. 4. Biosynthesis of Deutzia compounds.

3.2 Iridoids and some other glycosides in Hydrangeaceae

3.2.1 Hydrangeeae; Hydrangea

Loganin (1) was first reported (Plouvier, 1964) from three species of Hydrangea,

namely H. aspera D. Don, H. bretschneideri Dippel and H. xanthoneura Diels. This

compound has later been reported from H. hortensis Sm. (Khalifa et al., 2001) and H.

macrophylla (Yamamoto et al, 2002). Recently, the -glucopyranosyl ester of

deoxyloganic acid (11), namely 11a, was isolated from H. macrophylla subsp. serrata

(Thunb.) Makino (Kikuchi et al., 2008a).

O

OGlc

CHO COOMe

1

14 Secologanin

NH2

OH

OH

OH

OH NAc

OGlc

COOMe

15 Ipecoside

OO

OGlc

OHCH

3

18 Deutzioside

OO

OGlc

OH OHCH

3

19 Scabroside

O

OGlc

CH3

O

OGlc

OHCH

3

16 Decapetaloside

O

OGlc

CH3

OH

17 Loasaside9a Iridodial glucoside

7

Also, a number of aromatic esters of loganic acid (12) as well as loganin (1) and three

diglucosides of this has been reported from H. paniculata Sieb. (Shi et al., 2012).

Examples are (12a) and (1a).

Loganin (1), secologanic acid (13), secologanin (14) and sweroside (2) as well as four

derivatives of (14) named hydrangeosides A-D (20-23) were found in H. macrophylla

var. macrophylla (Inouye et al., 1980; Uesato et al., 1981).

A year later, three similar compounds, namely hydrangeosides E-F (24-26) were

reported from H. scandens (L. f.) Ser. (Uesato et al., 1982). In addition, in a final

paper (Uesato et al., 1984) the absolute structures of the seven compounds (20-26)

were elucidated. Hydrangeoside A (20) has also been reported from H. chinensis

Maxim. (Patnam et al., 2001), H. hortensis (Khalifa et al., 2001) together with the

dimethyl acetal of secologanin (14), a typical artifact formed from 14 when extracting

the plant material with methanol.

More recently, another variety of the plant, namely H. macrophylla var. thunbergii

Makino was investigated (Yoshikawa et al., 1994; Matsuda et al., 1999) to give the

somewhat different lactones hydramacroside A (27) and B (28). This study was later

O

OGlc

GlcO

COOMe

O

OGlc

COOH

O

OH O

MeOO

OGlc

COOGlc

11a 12a 7-Feruloylloganic acid 1a 7-OGlucopyranosyl -loganin

20 Hydrangeoside A

O

OGlc

COOMeOH

OH

O

O

OGlc

COOMeO

OH

O

O

H

26 Hydrangeoside G

O

OGlc

COOMe

OH

OH

O

H

24 Hydrangeoside E

O

OGlc

COOMe

OH

OH

O

H

25 Hydrangeoside F

21 Hydrangeoside B

O

OGlc

COOMeO

OH

O

O

H

O

OGlc

COOMe

OH

O

O

H

23 Hydrangeoside D

O

OGlc

COOMe

OH

O

O

H

22 Hydrangeoside C

8

extended by an investigation of the flowers of the same variety and gave

hydrangeoside A (20) as well as 27 and 28, and in addition the two alkaloids derived

from 28, namely the two epimers hydrangeamine A (29) and B (30) (Liu et al., 2013).

From a third taxon, H. macrophylla subsp. serrata was isolated hydrangeoside A (20)

and C (22) as well as the dimethyl acetal of 20 and a number of methyl and/or n-butyl

acetal derived from secologanin (14), secologanic acid (13) or morroniside (31)

(Sakai et al., 2007; Kanno et al., 2007). Such acetals are usually artifacts formed with

the solvents used during work-up. Further work with this plant provided the four

macropyllanosides A-D (32-35), cyclic acetals of 14 with glycerol D-

galactopyranoside, myo-inositol and shikimic acid (Kikuchi et al., 2008b).

An additional acetal of secologanin, this time with the cyanogenic glucoside

taxiphyllin, namely hydracyanoside D (36), was later reported from the parent H.

macrophylla (Wang et al., 2010) together with hydracyanoside F (37), secoxyloganin

(38) and 8-epiloganin (39).

27 Hydramacroside A 28 Hydramacroside B

O

OGlc

O O

OOH

OH

H

O

OGlc

O OH

OH

OOHO

29 Hydrangeamine A

N

O

OGlc

O OH

OH

30 Hydrangeamine B

N

O

OGlc

O OH

OH

O

OGlc

COOMe

O

OH

31 Morroniside 32 Macrophyllanoside A (R=Glyceryl)

O

OGlc

COOMeOO

HOOC

OH

H

O

OGlc

COOMeOO

H

OH

OHOH

OH

33/34 Macrophyllan- osides B and C

35 Macrophyllan- oside D

O

OGlc

COOMeO

OOH

OH

OOR

9

Finally, two esters of demethylsecologanol were isolated from H. paniculata (Shi et

al., 2014), namely hydrangeside B (40a) and methylgrandifloroside (40b).

3.2.2 Hydrangeeae; Others

Platycrater, Decumaria, Pileostegia, Broussaisia, Deinanthe, Cardiandra appears not

to have been properly investigated; of these, Decumaria and Broussaisia have only

been examined for flavonoids (Bohm et al, 1985). Dichroa febrifuga Lour., on the

other hand, is much used in Chinese medicine and has been well investigated.

However, no iridoids have been reported.

3.2.3 Philadelpheae; Deutzia

The compound scabroside (19) was the first iridoid glucoside isolated from D. scabra

Thunb. (Esposito and Guiso, 1973), quickly followed by deutzioside (18) (Bonadies et

al., 1974) and deutziol (41) (Esposito et al., 1976). Later, work was continued on this

plant and gave rise to scabrosidol (42) (Esposito et al., 1983) and the two aglucones

deutziogenin (18a) and scabrogenin (19a) (Esposito et al., 1984). The compounds 18

and 19 have also been isolated from D. crenata Sieb. et Succ. (Inouye et al., 1977)

and D. schneideriana Rehder (Frederiksen et al., 1999)

3.2.4 Philadelpheae; Kirengeshoma

In the present work we found loganin (1), sweroside (2), 6-β-hydroxysweroside (3)

and demethylalangiside (4).

36 Hydracyanoside D 37 Hydracyanoside F

O

OGlc

COOMe

OH

39 8-Epiloganin

O

OGlc

COOMeHOOC

38 Secoxyloganin

O

O

OGlc

COOMeO

O

OH

OH

OOH

CNH

O

OGlc

O ONC

O

OGlc

ROCOOH

40 R=H; Demethyl- secologanol

O

O

OHOH

OMe

O

OH

OMe

40a Hydrangeside B 40b Methylgrandifloroside

R= R=

OMe

O

OGlc

OHCH

3

OH

41 Deutziol

O

OGlc

OHCH

3

OH

OH

OH

42 Scabrosidol

O

OH

OHCH

3

O

18a Deutziogenin

O

OH

OHCH

3

O

OH

19a Scabrogenin

10

3.2.5 Philadelpheae; Others

The genera Philadelphus, Carpenteria, Whipplea, Fendlerella have all been

investigated for their flavonoid content (Bohm et al, 1985), but apparently not for

iridoids.

3.2.6 Jamesioideae; Jamesia

In the present work, we have isolated the compounds Arbutin (6), picein (7) and

prunasin (8), and no iridoids were present.

3.2.7 Jamesioideae; Fendlera

Apparently, no chemical work has been done on this genus.

3.3 Chemosystematics

The phylogenetic relationships based on the published DNA sequencing results are

shown in Fig. 1. From the above information, it is difficult to deduce much about the

chemical relationships within the Hydrangeaceae, since only six of the seventeen

genera appears to have been investigated properly for their content of iridoid

glycosides. However, some useful taxonomic information about the interfamilial

relationships can be drawn from the published chemical data. Thus, the iridoids in

Deutzia are closely related to those found in Mentzelia (Loasaceae) (Jensen et al.,

1981; El-Naggar et al., 1982) and they share a peculiar biosynthetic route

(Frederiksen et al., 1999) in formation of the 10-decarboxylated compounds (Fig. 3)

so far solely found in these two genera. In addition, the common occurrence of the

iridoid glucoside 6-β-hydroxysweroside (3) in Kirengeshoma and in Gronovia

scandens L. (Loasaceae) (Rodríguez et al., 2002) may be indicative, since 3 is a

compound that has never been reported from other taxa, and futhermore,

hydroxylation of the 6-position of secoiridoids appears to be almost unknown

otherwise. Taken together, this indicate a common ancestry of the two families

Hydrangeaceae and Loasaceae, as it is also found in the DNA sequence investigations

(Fig. 1). On the other hand, many of the simple iridoid glucosides shown in Fig. 2,

namely compounds 1, 11-14 and also 31 and 38 are shared between Hydrangea and

Loasaceae, but these compounds are common in most other families in Dipsacales

and Gentianales.

Hydrangeaceae also share many of the simple compounds above with Cornaceae,

however, the occurrence of the rare esters of loganin (1a and 12a) in Hydrangea

paniculata are particularly interesting since these same compounds are also reported

from Cornaceae, namely 1a from Alangium platanifolium (Sieb. & Zucc.) Harms

(Otsuka et al., 1996) and 5a from A. lamarckii Thwaites (Itoh et al., 2001). Similarly,

the finding of demethylalangiside (4) in Kirengeshoma is paralleled by the occurrence

of this and many similar ipecac alkaloids in Alangium (Itoh et al., 2001). Otherwise,

compounds from this biosynthetic pathway (Fig. 3) is solely found in a few genera of

Rubiaceae.

11

Acknowledgements

The research project is implemented within the framework of the Action «Supporting

Postdoctoral Researchers» of the Operational Program "Education and Lifelong

Learning" and is co-financed by the European Social Fund (ESF) and the Greek State.

We thank the staff of The Botanical Garden of Copenhagen for providing the plant

material and Dr. Larry Hufford, Washington State University for comments.

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17

Fig. 1. Cladogram of Hydrangeaceae based on maximum parsimony analyses of the

combined matK and rbcL data set. Sequences are downloaded from GenBank.

Numbers above branches are bootstrap values.