Synthesis of LoganVir, a new carbocyclic nucleoside analogue

Article abstract of DOI:10.1080/14786419.2016.1149831

Starting from a natural cyclopentanoid monoterpene belonging to the class of iridoid glucosides called loganin, we performed the synthesis of a new carbocyclic nucleoside, allowing the preparation of a new lead compound, with a potential HIV antiviral activity as an reverse transcriptase competitive inhibitor that we named LoganVir. The stereocontrol of the coupling reaction was completed utilizing the procedure described by Mitsunobu with a purinic base.

Full text of DOI:10.1080/14786419.2016.1149831

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: http://www.tandfonline.com/loi/gnpl20
Synthesis of LoganVir, a new carbocyclic
nucleoside analogue
Luigi Ornano & Armandodoriano Bianco
To cite this article: Luigi Ornano & Armandodoriano Bianco (2016): Synthesis of
LoganVir, a new carbocyclic nucleoside analogue, Natural Product Research, DOI:
10.1080/14786419.2016.1149831
To link to this article: http://dx.doi.org/10.1080/14786419.2016.1149831
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Date: 17 March 2016, At: 23:07

Natural Product research, 2016
ꢁꢁp://ꢂx.ꢂꢃi.ꢃꢄg/10.1080/14786419.2016.1149831
ꢀ
Synthesis of LoganVir, a new carbocyclic nucleoside analogue
Luigi Ornanoa,b and Armandodoriano Biancoa,b
ꢅ
b
dipꢅꢄꢁimꢆnꢁꢃ ꢂi cꢀimiꢇꢅ, univꢆꢄꢈiꢁà ꢂi rꢃmꢅ“lꢅ sꢅpiꢆnzꢅ”, rꢃmꢅ, Iꢁꢅꢉy; cꢃnꢈꢃꢄziꢃ cꢃsMꢆsꢆ, dipꢅꢄꢁimꢆnꢁꢃ ꢂi
sꢇiꢆnzꢆ ꢂꢆꢉꢉꢅ Viꢁꢅ ꢆ ꢂꢆꢉꢉ’ambiꢆnꢁꢆ, univꢆꢄꢈiꢁà ꢂi cꢅgꢉiꢅꢄi, cꢅgꢉiꢅꢄi, Iꢁꢅꢉy
ABSTRACT
ARTICLE HISTORY
rꢆꢇꢆivꢆꢂ 12 aꢊgꢊꢈꢁ 2015
aꢇꢇꢆpꢁꢆꢂ 30 Jꢅnꢊꢅꢄy 2016
Starting from a natural cyclopentanoid monoterpene belonging
to the class of iridoid glucosides called loganin, we performed the
synthesis of a new carbocyclic nucleoside, allowing the preparation
of a new lead compound, with a potential HIV antiviral activity as an
reverse transcriptase competitive inhibitor that we named LoganVir.
The stereocontrol of the coupling reaction was completed utilizing
the procedure described by Mitsunobu with a purinic base.
KEYWORDS
anꢁiviꢄꢅꢉ ꢅgꢆnꢁꢈ; ꢁꢆꢄpꢆnꢃiꢂꢈ;
ꢄꢆꢅꢄꢄꢅngꢆmꢆnꢁꢈ; ꢇꢀiꢄꢅꢉ
inꢁꢆꢄmꢆꢂiꢅꢁꢆꢈ; ꢈynꢁꢀꢃnꢈ
1
. Introduction
The carbocyclic nucleoside analogues are an important class of antiviral agents, particularly
when used against HIV infection. Carbocyclic nucleosides are included in the class of reverse
transcriptase (RT) inhibitors (Mehellou & De Clerq 2010; Matyugina et al. 2012). Nucleosides,
as lead compounds, are fundamental building blocks of biological systems, and display a
wide range of biological activity. Through kinases, they are phosphorylated into their mono-,
di- and triphosphates, and the resulting nucleotides are processed into nucleic acids by pol
-
ymerases (Mehellou & De Clercq 2009). There has been an intense research into nucleoside
analogues, which function as non-toxic, selective inhibitors of kinases and polymerases
for the control of viral diseases and cancer (Borthwick et al. 1990; Agrofoglio et al. 1994).
Consequently, extensive modifications have been made to both the heterocyclic base and
the sugar moiety in order to avoid the drawbacks exhibited by nucleosides or analogues
in certain applications, mainly due to enzymatic degradations. The carbocyclic nucleosides
CONTACT lꢊigi oꢄnꢅnꢃ
ꢉꢊigi.ꢃꢄnꢅnꢃ@ꢊniꢄꢃmꢅ1.iꢁ
sꢊppꢉꢆmꢆnꢁꢅꢉ ꢂꢅꢁꢅ fꢃꢄ ꢁꢀiꢈ ꢅꢄꢁiꢇꢉꢆ ꢇꢅn bꢆ ꢅꢇꢇꢆꢈꢈꢆꢂ ꢅꢁ ꢀꢁꢁp://ꢂx.ꢂꢃi.ꢃꢄg/10.1080/14786419.2016.1149831.
©
2016 tꢅyꢉꢃꢄ & Fꢄꢅnꢇiꢈ

2
L. ORNANO AND A. BIANCO
are different from nucleosides since a methylene group is present instead of the oxygen
present in the furan of the nucleosides. The presence of a methylene group in the place of
the oxygen in the position adjacent to the carbonium in which the heterocyclic base is linked
characterises the carbocyclic nucleosides since the bond is no longer a glycosidic one but
an aminic one, therefore resulting in stable division of phosphorylases and hydrolases. The
structure similarity of carbocyclic nucleosides and normal nucleosides guarantees useful
interactions with other enzymes involved in nucleoside metabolism in order to be used in
potential therapeutic interventions (Marquez 1996). The understanding of the virus struc-
ture and its replication mechanism influences the design of the aforementioned inhibitors.
The interaction mechanism of the inhibitors can be understood by analyzing the action of
RT. The single viral stranded RNA is used by the RT enzyme as a template for the synthesis
of double helix DNA. Firstly, the RT links the template primers, and, subsequently, it links
a new deoxyribonucleoside triphosphate (dNTP). The chain elongation, which is catalysed
by DNA polymerase, is a nucleophilic attack of the 3′-OH – that is terminus of the primer
on the innermost phosphorous atom of a dNTP. The concurrent release of pyrophosphate
forms a phosphodiester bridge (Mitsuya et al. 1986; De Clercq 2005). Nucleoside carbocyclic
analogues have the role to act as competitive inhibitors of RT; at the same time, because of
the lack of the 3′-OH function, these analogues act as chain terminators. Numerous natural
products of biological interest, e.g. prostaglandins and similar derivatives, have the presence
of the cyclopentane template. This template has been introduced in the molecular structure
of nucleosides as a substitute for furanose moiety and deoxyribose (Bindu Madhavan &
Martin 1986). Loganin, a natural monoterpenoid belonging to the class of natural products
called iridoids, was chosen by us as a starting material for the synthetic process of enantio-
merically pure cyclopentane moiety. This starting synthon has the right chemical function in
the right position for the heterocyclic base to be inserted, giving new carbocyclic nucleoside
analogues, which have a highly functionalised cyclopentane ring as a feature. In particular,
aucubin and antirrhinoside were previously used as synthons for new carbocyclic nucleoside
analogues (Bianco & Mazzei 1997; Bianco et. al. 2001a; Bianco et al. 2001b).
2
. Results and discussion
We report the synthesis of a new carbocyclic nucleoside analogue using loganin 2 as the
starting material, which is a methyl-cyclopentanoid glucoside present as loganic acid in
Vinca difformis subsp. Sardoa. We chose this plant because it turned out to be rich in loganin
and loganic acid (Bianco et al. 2005). V. difformis subsp. Sardoa samples were collected at
the beginning of June 2013 from a natural population which grows in southern Sardinia
(
Diga Corsi, Iglesias (IT); V. sardoa is an endemic species of the Sardinia Island, a sample was
stored in the Botanical Garden of the Università di Cagliari. This sample of V. sardoa was first
dried in a ventilated thermostat oven, then it was put in extraction and the crude extract
was lyophilised in order to obtain the dried extract. The isolation of the iridoidic fraction was
performed by means of absorption/desorption chromatography through the use of charcoal.
This desorption process allowed the isolation of three eluites, as specified in the experimental
section, giving three different solutions, one of which contained loganic acid only and the
other two a mixture of loganin/loganic acid. The carbocyclic nucleoside 8 has the hydrox-
ymethyl function and shows further hydroxylated functions. We prepared a highly function-
alised carbocyclic nucleoside analogue so that we could verify, in the presence of several

NATURAL PRODUCT RꢀSꢀARCH
3
Scheme 1. synꢁꢀꢆꢁiꢇ pꢄꢃꢁꢃꢇꢃꢉ ꢅppꢉiꢆꢂ.
functions on the cyclopentane ring, whether the nucleoside analogue could be accepted
as substrate by cellular kinase, therefore inhibiting the RT. Compound 8, which we named
LoganVir, has the structure of the 2-((3R,4R)-4-(6-amino-9H-purin-9-yl)-2-(hydroxymethyl)-
3-methylcyclopentyl)propane-1,3-diol. The synthetic strategy is described in scheme 1. The
synthetic procedure is described as follows: the isolation process gave spectroscopically
pure loganic acid; therefore, we decided to convert it into its derived methylester called
loganin 2 by treating it with diazomethane, a specific reagent for the esterification of the
1
13
carboxylic function group. Loganin was characterised through means of H NMR, C NMR
spectroscopy and ꢀSI mass spectrometry. Product 2 was characterised comparing it with
the data reported in literature (Güvenalp et al. 2006); signals of the iridoidic nucleus were
revealed, namely methyl function in position C-10 at 1.08 ppm, carbomethoxylic function
in C-11 at 3.67 ppm, the H-3 olefinic proton at 7.37 ppm and the H-1 hemiacetalyc proton at
5.73 ppm. The synthetic approach used in this procedure was based on six synthetic steps: the
enzymatic hydrolysis of the β glycosidic bond led to the loss of the glycosidic residue without
compromising the enantiomeric puricy of the iridoic nucleus; the second step concerned
the reduction of both the enol-ether cyclic system (also known as cyclic hemiacetal) and of
the ester function. The third synthetic step adopted in this procedure regarded the selective
protection of the primary alcohol functions maintaining the secondary alcohol function free
for the insertion of the heterocyclic base. This insertion was performed only after replacing
the secondary alcohol function in its acetylic function, which represents the fourth synthetic
step. The fifth step was the link between the carbocyclic nucleus and the heterocyclic base

4
L. ORNANO AND A. BIANCO
by means of Mitsunobu methodology. The heterocyclic base we used in this procedure was
N-6 Benzoyl protected adenine. The last step of this synthetic procedure was a one-step total
deprotection of all protecting groups giving the target that we called LoganVir. ꢀnzymatic
hydrolysis was achieved by means of ß-glucosidase. The proton spectrum highlights the
absence of the signals linked to the glucosidic residue. The carbon spectrum highlights the
C-3 cyclic enol-ether, the carbomethoxylic system and the carbons of the dihydropyranic
bridge. The aglicon 3 was treated with an excess of NaBH by using water as a solvent. This
4
reduction gave compound 4 with a 90% yield; NaBH also led to the reduction of the meth-
4
ylester function; this is caused by the usage of water as a solvent which we suppose could
improve the reduction features of the NaBH (Bianco et al. 1988) Through means of NMR,
4
.
the intermediate 4 revealed the absence of the dihydropyranic signals and of the ester sys-
tem in C-11 position; the positive ion mode ꢀSI-MS spectrum revealed the presence of the
adduct with ion Na. The obtained intermediate 4 contains three primary alcohol functions
which were regioselectively protected with an isobutyryl residue giving the triester. The
regioselectivity was obtained through a rigorous control of both temperature and reaction
time; the former was kept constant at 0 °C during the reaction which was quenched with cold
methanol after one hour and a half. A good regioselectivity was obtained thanks to a strict
control of the quenching time as well. After exceeding the 1.5 h limit, the secondary alcohol
function reacts and the unwanted protection of it is obtained, therefore losing the regioselec-
tivity. The control of these parameters led to the protection of all primary alcohol functions
present in the sample. The adopted method allowed us to have the intermediate 5. The
compound 9 formed as a minor by-product was isolated during column chromatography,
purification of the intermediate 5 was recycled after transesterification to the intermediate
4
6
. The secondary alcohol function of 5 was then acetylated obtaining the key intermediate
in quantitative yield. We decided to employ the Mitsunobu methodology to link the nucle-
obase and the synthons 6 (Mitsunobu 1981; Hughes et al. 1996; Kumara Swamy et al. 2009).
The reaction between 6 and N6-benzoyl adenine has been accomplished by Mitsunobu
methodology; after 18 h the reaction was complete and the orange oily residue, obtained
after evaporation of solvents, was purified by column chromatography to give pure product
7
as white powder. The one-step hydrolysis of all protective groups in 7 was performed by
the treatment with DIBAL and the crude product was purified by column chromatography,
giving pure LoganVir 8 as a colourless powder. The one-step hydrolysis of all protective
groups in 7 was performed by the treatment with DIBAL (Diisobutylaluminium hydride)
and the crude product was purified by column chromatography, giving pure LoganVir 8 as
a colourless powder. Biological tests are in progress.
3
. Experimental
3
.1. Plant material and isolation
V. difformis subsp. sardoa samples were collected at the beginning of June 2013 from a nat-
ural population which grows in southern Sardinia (Diga Corsi, Iglesias (IT)); V. sardoa is an
endemic species of the Sardinia Island. The voucher specimen was identified by Dr. Cinzia
Sanna (Consorzio InterUniversitario di Ricerca‘Co.S.Me.Se ’, Dipartimento della Vita e dell’Am-
biente, Università di Cagliari) which was then stored (Herbarium CAG 736) in the General
Herbarium of the botanical garden of the University of Cagliari. About 500.0 g of the aerial

NATURAL PRODUCT RꢀSꢀARCH
5
parts of V. sardoa were dried about 48 h in a ventilated thermostat oven at 40 °C. The dried
plant materials were extracted with 96% ethanol (3 × 500 mL each). The obtained extract
was concentrated under reduced pressure in order to eliminate the ethanol. The resulting
water suspension was first frozen at −20 °C and the residue was lyophilised to recover 35 g
of the crude extract. The total crude extract was suspended in a water solution with charcoal
(
about 100 g) until the negative Vanilline test, and the resulting suspension was filtered
through a gooch funnel. ꢀlution with water and water-10% ꢀtOH removed all the salts and
sugars, whereas 30, 60 and 90% ꢀtOH eluted the iridoid-contanining fraction. The fraction
eluted with 60% ethanol was purified by chromatography with CHCl –CH OH (7:3) system,
3
3
1
13
obtaining 220 mg of pure loganic acid, which was identified through the H NMR- C NMR
and ꢀSI-MS, in line with the data present in literature.
Loganic Acid (1): H NMR- 13C NMR and ꢀSI-MS data are shown in the supplementary
1
section (S1, S2, S3).
3
.2. Synthesis
3
.2.1. Loganin (2)
4
68 mg of compound 1 and 10 mL of CH OH, were added to 20 mL of a CH N /ꢀt O solution
3 2 2 2
giving a yellow cloudy mixture, and the mixture was left at room temperature for 20 min
until slow complete decolouration. The reaction mixture was bubbled with CO for 10 min
2
until complete removal of excess diazomethane . The crude product was purified by column
chromatography on silica gel (BuOHsat) to give 428 mg of an amorphous brown powder
1
13
(
87.9% yield). H NMR- C NMR and ꢀSI-MS data and spectra are shown in S1, S2 and S3.
3
.2.2. Loganin Aglicon (3)
Methyl-(1R,6S,7R)-1,6-dihydroxy-7-methyl-1,4a,5,6,7,7a-hexahydrocyclopenta[c]pyran-4-
carboxylate. Compound 2 (150 mg) was dissolved in water (5 mL) and β-glucosidase (ꢀC
3
3
.2.1.21, Sigma Almond Meal, 225 mg) was added to the solution. This mixture was left at
7 °C inside the incubator for 24 h. The reaction was monitored by TLC using chloroform/
methanol (7:3). The reaction mixture was filtered through a gooch funnel, and the filtrate was
extracted three times with ꢀtOAc. The combined organic layers were dried with anhydrous
Na SO , filtered and the solvents were evaporated in vacuo to leave the compound 3 (75 mg,
2
4
1
8
5.5% yield). H NMR, (300 MHz, D O) δ: 0.93 (3H, m, H-10), 1.14–1.47 (2H, m, H-6), 1.78 (1H,
2
m, H-8), 1.47 (1H, m, H-5), 2.92 (H-9, m, 3.59 (3H, s,-OMe), 3.46 (1H, m, H-7), 5.1 (1H, m, H-1),
1
3
7
4
ꢀ
.53 (1H, m, H-3), 2.0 (1H, m, H-5). C NMR, (75 MHz, D O), δ: 12.8 (C-10), 31.3 (C-5), 40.8 (C-8),
2
0.9 (C-6) 46.1 (C-9), 51.9 (OMe), 74.2 (C-7) 95.4 (C-1), 111.5 (C-4), 153.2 (C-3), 170.4 (C-11).
SI-MS: m/z = 251.0257 [M-Glu + H O + Na] (calculated mass C H O (228.2440). H NMR-
C NMR and ꢀSI-MS spectra are shown in S4, S5 and S6.
+
1
2
11 16
5
1
3
3
2
.2.3. Loganinol (4)
-((1S,2S,3R,4S)-4-hydroxy-2-(hydroxymethyl)-3-methylcyclopentyl)propane-1,3-
diol. Compound 3 (47 mg) was dissolved in water (5 mL) and a 10 fold excess of NaBH4
was added port wise to the stirred solution. After 20 min, the reaction was complete, as
shown by TLC using chloroform/methanol (7:3). The solution was neutralised with CO2
gas. Charcoal was then added to the solution to absorb organic materials and the level of
absorption was checked by H SO test. The resulting mixture was filtered through a gooch
2
4

6
L. ORNANO AND A. BIANCO
funnel and first washed to eliminate the salts, for desorbtion was then washed with boiling
methanol. The methanolic solution was concentrated in vacuo and the product 4 was purified
by chromatography, eluting it with chloroform/methanol (8:2). The product was obtained
1
as yellow powder (36 mg, 85.5% yield). H NMR, (300 MHz, CD OD), δ: 0.77 (1H, m, H-2′), 0.90
3
(
2H, m, H-3, H-4), 1.00 (1H, m, H-4′), 1.16 (3H, d, J = 6.0 Hz, H-2), 1.46 (2H, m, H-5), 1.90–2.25
(
4H, m, H-4″), 3.22 (2H, m, H-3′), 3.57 (1H, m, H-1), 4.0 (1H, m, C -OH), 5.2 (3H, m, C4″-3′-OH).
1
1
3
C NMR, (75 MHz, D O), δ: 14.2 (C-2′), 41.4 (C-2), 35.7 (C-5), 36.9 (C-4), 47.4 (C-3), 41.44 (C-4′),
2
+
6
1.3 (2C-4″-4″), 62.16 (C-3′), 73.8 (C-1). ꢀSI-MS: m/z = 227.1517 [M + Na] (calculated mass
C H O 204.2660), (S7, S8, S9).
1
0
20
4
3
2
.2.4. Isoburyl-derivative (5)
-((1S,2S,3R,4S)-4-hydroxy-2-((isobutyryloxy)methyl)-3-methylcyclopentyl)propane-1,3-
diyl bis(2-methylpropanoate). The reaction was accomplished by dissolving 4 (50 mg) in
pyridine (0.7 mL) followed by the addition of isobutyric anhydride (0.2 mL) at 0 °C. After 1.5 h,
the starting product was no longer present in the reaction mixture; it was then quenched by
adding methanol at 4 °C (5 mL). The reaction mixture was diluted with ꢀtOAc (10 mL), org.
phase separated, washed with 2 N HCl, then with brine until neutral; the residue obtained
after evaporation in vacuo of the volatile material, was chromatographed on silica gel with
hexane/AcOꢀt (1:1), affording pure 5 (96 mg, 94.6% yield). The rest being tetrabutyroyl
1
derivate. H NMR, (300 MHz, CD Cl) δ: 0.85 (H-2′, m, 3H), 1.18 (12H, m, (CH ) CHCO), 1.23–1.28
3
3 2
(
2H, m, H-2, H-4), 1.59 (1H, m, H-3), 1.99 (2H, m, H-5), 2.32 (3H, m, (CH ) CHCO), 2.56 (1H, m,
3 2
1
3
H-4′), 3.46 (1H, m, H-1), 3.64 (4H, m, H-4″), 4.08 (1H, m, OH-1), 5.32 (1H, m, H-3′). C NMR,
(
75 MHz, CD Cl), δ: 14.61 (C-2′), 18.63–18.75–18.78–18.83–18.88–19.00 ((6x (CH ) CHCO),
3
3
2
33.90–34.19 (3x (CH ) CHCO), 33.93 (C-4′), 34.89 (C-5), 38.31 (C-4), 44.97 (C-2), 50.28 (C-3),
3 2
6
4.46 (C-3′), 63.11 (2C-4″), 183.67–176.86–172.74 ((CH ) CHC=O). ꢀSI-MS: m/z = 437.3059
3
2
+
[
M + Na] (calculated mass C H O 414.5390), (S10, S11, S12).
22 38 7
3
2
.2.5. Acetyl-derivative (6)
-((1S,2S,3R,4S)-4-acetoxy-2-((isobutyryloxy)methyl)-3-methylcyclopentyl)propane-1,3-
diyl bis(2-methylpropanoate). The reaction was accomplished by dissolving 5 (100 mg) in
pyridine (0.7 mL) followed by the addition of acetic anhydride (0.35 mL) at room temperature.
After 2 h, the starting product was no longer present in the reaction mixture, it was quenched
by adding methanol at 4 °C (5 mL). After work up, the mixture was then diluited with ꢀtOAc
(
10 mL) washed with 2 N HCl and successively with brine solution (NaCl ) until neutrality. The
sat
residue, obtained after evaporation in vacuo of the volatile material, was chromatographed
1
on silica gel with chloroform/ diethylether (9:1) to afford pure 6 (109 mg, 98.9% yield). H
NMR, (300 MHz, CD Cl) δ: 0.87 (H-2′, m, 3H), 1.14–1.24 (12H, m, (CH ) CHCO), 1.29 (2H, m, H-2,
3
3 2
H-4), 1.60 (1H, m, H-3), 1.70 (2H, m, H-5), 2.01 ((CH3CO), 2.32 (3H, m, (CH ) CHCO), 2.52 (2H, m,
3
2
13
H-4′), 4.01 (1H, m, H-1), 3.65 (4H, m, H-4″), 5.32 (1H, m, H-3′). C NMR, (75 MHz, CD Cl), δ: 14.75
3
(
C-2′), 18.74–18.86–20.70–20–95((6x (CH ) CHCO), C-8″, C-9″), 29.65 (CH3CO) 33.70–33.95
3 2
(
3x (CH ) CHCO), 2C-8′. C-9′), 33.95 (C-4′), 36.29 (C-5), 37.01 (C-4), 41.12 (C-2), 45.01 (C-3),
3 2
6
4.44 (C-3′), 62.92–63.12 (2C-4″), 75.89 (C-1), 183.67–176.86–172.74 ((CH ) CHCO). ꢀSI-MS:
3 2
+
m/z = 437.3059 [M + Na] (calculated mass C H O Na 436.5208). ꢀSI-MS: m/z = 479.1472
2
2
37
7
+
[
M + Na] (calculated mass C H O 456.5760), (S13, S14, S15).
24 40 8

NATURAL PRODUCT RꢀSꢀARCH
7
3
2
.2.6. LoganVir- Protected (7)
-((1S,2S,3R,4R)-4-(6-benzamido-9H-purin-9-yl)-2-((isobutyryloxy)methyl)-3-
methylcyclopentyl)propane-1,3-diyl bis(2-methylpropanoate). Compound 6 (50 mg) was
6
dissolved in anhydrous THF (0.5 mL) under argon atmosphere. N - benzoyladenine (50 mg)
and PPh (100.5 mg) were added to the solution. After 10 min, a solution of DꢀAD (0.1 mL)
3
in anhydrous THF (0.5 mL) was added at room temperature, maintaining an anhydrous
atmosphere. After 18 h, the reaction completed as shown by TLC and eluted with hexane/
AcOꢀt (1:1). The solution was concentrated to dryness in vacuo. The oily residue was
purified by chromatography using Hexane/AcOꢀt (1:1) as eluent. The product 7 (35 mg,
1
5
0.3% yield) was obtained as white powder. H NMR, (300 MHz, CDCl ), δ: 1.01–1.22 (3x
3
(
CH ) CHCO), 3x H-2′, H-10, br s), 1.65 (3H, m, H-2, H-5), 1.84 (1H, m, H-2), 3.52 (2H, m, H-4′,
3 2
H-1), 3.98–4.01 (6H, m, H-3′, H-4″), 7.25–7-95 (CH-aromatics), 8.51 (1H, s, H-8, adenine); 8.78
(
1H, s, H-2, adenine). 13C NMR, (75 MHz, CDCl ), δ:13.77 (CH ) CHCO), 14.26 (C-2′), 33.81 (2x
3
3 2
CH ) CHCO), 34.02 (CH ) CHCO), 25.36 (C-2); 29.42 (C-4), 33.81 (C-5), 40.94 (C-4′), 49.74 (C-3),
3
2
3 2
6
1
3.04–64.08 (C-4″), 67.62 (C-3′), 75.5 (C-1), 128.30 (C-H, aromatics), 128.54 (C-H, aromatics),
31.17 (C-H, aromatics), 132.56 (C-H, aromatics), 133.33 (C-H, aromatics), 137.00 (C-quaternary,
aromatics, C-5 adenine), 150.43 (C-8, adenine), 152.14 (C-2, adenine), 155.67 (C-4, adenine);
56.96 (C-6, adenine),166.72 (CO-benzoyl), 176,32–176.54–176.77 (3x (CH ) CHCO). ꢀSI-MS:
1
3
2
+
m/z = 637.0273 [M + H] (calculated mass C H N O 635.7620), (S16, S17, S18).
3
4
45
5
7
3
2
.2.7. LoganVir-(8)
-((1S,2S,3R,4R)-4-(6-amino-9H-purin-9-yl)-2-(hydroxymethyl)-3-methylcyclopentyl)
propane-1,3-diol. Compound 7 (25 mg) was dissolved in CH Cl (2 mL) and treated with
2
2
DIBAL in hexane (1.3 mL of a 1 M solution) at −78 °C for 2 h. After bubbling CO through the
2
mixture for a few minutes, the volatile materials were evaporated in vacuo and the residue
was chromatographed on silica gel with chloroform/methanol (6:4) to give LoganVir 8
1
(
(
12.6 mg, 100% yeld) as a powder. H NMR, (300 MHz, CDCl , δ: 0.50 (2H, m, H-3,H-4); 0.88
3
4H, m, H-4′, H-2, H-5); 2.93 (4H, m, H-4″); 3.23 (2H, m, H-3′), 3.45 (1H, m, H-3′), 3.8–3.7 (3H, m,
C-4″-OH, C-3′-OH), 7.06 (2H, bs, –NH ), 7.82 (1H, s, H-2- adenine); 8.90 (1H, s, H-8- adenine).
2
13
C NMR, (75 MHz, CDCl ), δ: 13.53 (C-2′), 13.92 (C-2), 19.39 (C-4), 49.10 (C-5), 51.84 (C-1), 60.83
3
(C-4′), 61.23 (C-3), 63.05 (C-3′), 63.77 (2X C-4″), 128.05 (C-5 adenine), 131.51 (C-8 adenine),
1
50.06 (C-4 adenine), 151.81 (C-2 adenine), 156.77 (C-6 adenine). ꢀSI-MS: m/z = 321.0364
+
[
M + H] (calculated mass C H N O 321.3810), (S19, S20, S21).
1
5
23
5
3
3
.2.8. Loganinol recycled from tetrabutyroyl-derivative (9)
Compound 9 (50 mg) was dissolved in MeOH (10 ml), and treated with Na; at 0 °C for 5 min.
The reaction mixture was left at room temperature. After 15 min the reaction was complete,
as shown by TLC using chloroform/methanol (8:2). The solution was neutralised with CO2
gas. Charcoal was the added to the solution to absorb organic materials. The adsorption
of organic material was obtained by adding charcoal to the solution, and the adsorption
degree was checked by TLC with H SO test. The resulting suspension was filtered on a
2
4
gooch funnel and then washed first to eliminate the salts, and then with boiling methanol.
The methanolic solution was concentrated in vacuo and the product 4 was purified by chro-
matography, eluting with chloroform/methanol (8:2). The product was obtained as yellow
powder (23 mg, 100% yield).

8
L. ORNANO AND A. BIANCO
4
. Conclusion
In this work, we synthesised a new carbocyclic nucleoside analogue which we named
LoganVir, starting from a substrate of natural product that is called loganin, a monoterpenoid
belonging to the class of iridoids. The synthetic procedure is a linear synthesis, which consists
of few synthetic steps, namely six steps, and each step has some high yields; this makes the
process particularly interesting. ꢀvery reaction had the dual purpose of maintaining the
enantiomerically pure moiety unchanged and we performed aimed modifications to the
dihydropiranic system with the goal of obtaining a carbocylic system; this carbocyclic system
has shown to be variously functionalised with a good synthetic flexibility. The carbocyclic
alcohol intermediate four presents synthetic flexibility since its free alcohol functions can be
replaced with the possibility of giving new analogues which can show different functions.
Once we obtained the carbocyclic intermediate, we carried out the insertion of the hetero-
cyclic base in it. Finally, by performing the removal of the isobutyryl and benzoyl systems in
one step, we reached our goal, namely the new carbocyclic nucleoside analogue, LoganVir.
It is currently being tested for antiviral activity as a competitive inhibitor of RT.
Disclosure statement
No potential conflict of interest was reported by the authors.
ORCID
Armandodoriano Bianco
http://orcid.org/0000-0001-8622-5742
References
Agrofoglio L, Suhas ꢀ, Farese A, Condom R, Richard Challand S, ꢀarl RA, Guedj R. 1994. Synthesis of
carbocyclic nucleosides. Tetrahedron. 50:10611–10670.
Bianco A, Mazzei RA. 1997. Synthesis of a new carbocyclic nucleoside analog. Tetrahedron. 38:5433–
6436.
Bianco A, Passacantilli P, Righi G. 1988. Improved procedure for the reduction of esters to alcohols by
sodium borohydride. Synth Comm. 18:1765–1771.
Bianco A, Celona D, Di Rita S, Guiso M, Melchioni C, Umani. 2001a. Chiral synthons from the iridoid
glucoside antirrhinoside- synthesis of a carbocyclic homonucleoside analogue. ꢀur J Org Chem.
4061–4066.
Bianco A, Celletti L, Mazzei RA, Umani F. 2001b. Synthesis of aucubovir II, a new carbocyclic nucleoside
analog. ꢀur J Org Chem. 1331–1334.
Bianco A, Guiso M, Nicoletti M, Foddai S, Piccin A, Serafini M, Ballero M, Poli F. 2005. A comparative
chemotaxonomic study on Vinca sardoa stearn and Vinca difformis pourret. Nat Prod Res. 19:615–617.
Bindu Madhavan GV, Martin JC. 1986. A novel and sterespecific synthesis of (±) and (-) –aristeromycin.
J Org Chem. 51:1287–1293.
Borthwick AD, ꢀvans DN, Kirk Bꢀ, Biggadike K, ꢀxall AM, Youds P, Roberts SM, Knight DJ., Coates JAV.
1990. Fluoro carbocyclic nucleosides: synthesis and antiviral activity of 2'- and 6'-fluoro carbocyclic
pyrimidine nucleosides including carbocyclic 1-(2-deoxy-2-fluoro-.beta.-D-arabinofuranosyl)-5-
methyluracil and carbocyclic 1-(2-deoxy-2-fluoro-.beta.-D-arabinofuranosyl)-5-iodouracil. J Med
Chem. 33:179–186.
De Clercq ꢀ. 2005. New approaches toward anti-HIV chemotherapy. J Med Chem. 48:1297–1313.
Güvenalp Z, Kilic N, Cavit Z, Kaya Y, Demirezer LO. 2006. Chemical constituents of galium tortumense.
Turk J Chem. 30: 515–523.

NATURAL PRODUCT RꢀSꢀARCH
9
Hughes DL. 1996. Progress in the Mitsunobu Reaction. Organic Preparations and Procedures
International. 28(2):127–164. doi:10.1080/00304949609356516.
Kumara Swamy KC, Bhuvan Kumar NN, Balaraman ꢀ, Pavan Kumar KVP. 2009. Mitsunobu and related
reactions: Advances and application. Chem. Rev. 109:2551–2651.
Marquez Vꢀ. 1996. Carbocyclic nucleosides. Adv Antiviral Drug Des. 2:89–146.
Matyugina ꢀS, Khandazhinskaya AL, Kochetkov SN. 2012. Carbocyclic nucleoside analogues:
classification, target enzymes, mechanisms of action and synthesis. Russ Chem Rev. 81:729–746.
Mehellou Y, De Clercq ꢀ. 2009. Twenty-six years of anti-HIV drug discovery: where do we stand and
where do we go? J Med Chem Perspect.
Mitsunobu O. 1981. The Use of Diethyl Azodicarboxylate and Triphenylphosphine in Synthesis and
Transformation of Natural Products. Synthesis. 1981(1):1–28. doi:10.1055/s-1981-29317.
Mitsuya H, Broder S. 1986. Inhibition of the in vitro infectivity and cytopathic effect of human
T-lymphotrophic virus type III/lymphadenopathy-associated virus (HTLV-III/LAV) by
2 ', 3'-dideoxynucleosides. Proc Natl Acad Sci USA. 83:1911–1915.
Mitsuya H, Jarrett RF, Cossman J, Cohen OJ, Kao CS, Guo HG, Reitz MS, Broder S. 1986. Infection of
human T lymphotropic virus-I-specific immune T cell clones by human T lymphotropic virus-I. J
Clin Invest. 78:1302–1310.