Copper(II)nitrate catalyzed regioselective protection of primary alcohols with 4,4′-dimethoxytrityl and 2,7-dimethyl-9-phenyl xanthen-9-yl groups in nucleosides and carbohydrates

Article abstract of DOI:10.1080/15257770.2018.1460480

Regioselective protection of primary hydroxyl group in nucleoside and carbohydrate analogs was accomplished using dimethoxytrityl alcohol (DMTr-OH) or dimethylpixyl alcohol (DMPx-OH) in presence of copper(II)nitrate as a Lewis acid catalyst. Excellent selectivity was observed for the protection of primary hydroxyl group over secondary while glycosidic bond remain unaffected. Utility of this methodology was further exemplified via DMTr- and DMPx-protection of alipahtic acyclic and cyclic diols.

Full text of DOI:10.1080/15257770.2018.1460480

Nucleosides, Nucleotides and Nucleic Acids
ISSN: 1525-7770 (Print) 1532-2335 (Online) Journal homepage: http://www.tandfonline.com/loi/lncn20
Copper(II)nitrate catalyzed regioselective
protection of primary alcohols with 4,4′-
dimethoxytrityl and 2,7-dimethyl-9-phenyl
xanthen-9-yl groups in nucleosides and
carbohydrates
Srishylam Penjarla, S. Rajendra Prasad, Dhande Sudhakar Reddy,
Shyamapada Banerjee, Santhosh Penta & Yogesh S. Sanghvi
To cite this article: Srishylam Penjarla, S. Rajendra Prasad, Dhande Sudhakar Reddy,
Shyamapada Banerjee, Santhosh Penta & Yogesh S. Sanghvi (2018): Copper(II)nitrate catalyzed
regioselective protection of primary alcohols with 4,4′-dimethoxytrityl and 2,7-dimethyl-9-phenyl
xanthen-9-yl groups in nucleosides and carbohydrates, Nucleosides, Nucleotides and Nucleic
Acids, DOI: 10.1080/15257770.2018.1460480
To link to this article: https://doi.org/10.1080/15257770.2018.1460480
Published online: 03 May 2018.
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NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
, VOL. , NO. , –
https://doi.org/./..
Copper(II)nitrate catalyzed regioselective protection
of primary alcohols with ,ꢀ-dimethoxytrityl and
,-dimethyl--phenyl xanthen--yl groups in nucleosides
and carbohydrates
Srishylam Penjarlaa,b, S. Rajendra Prasada, Dhande Sudhakar Reddya,
Shyamapada Banerjeea, Santhosh Pentab, and Yogesh S. Sanghvic
aResearch & Development, Sapala Organics Private Ltd., IDA Mallapur, Hyderabad, India; bChemistry
Department, National Institute of Technology, Raipur G.E. Road, Raipur, Chhattisgarh, India; cProcess
Chemistry, Rasayan Inc., Encinitas, CA, USA
ABSTRACT
ARTICLE HISTORY
Received  February 
Revised  March 
Accepted  March 
Regioselective protection of primary hydroxyl group in nucle-
oside and carbohydrate analogs was accomplished using
dimethoxytrityl alcohol (DMTr-OH) or dimethylpixyl alcohol
(DMPx-OH) in presence of copper(II)nitrate as a Lewis acid
catalyst. Excellent selectivity was observed for the protection
of primary hydroxyl group over secondary while glycosidic
bond remain unaffected. Utility of this methodology was further
exemplified via DMTr- and DMPx-protection of alipahtic acyclic
and cyclic diols.
KEYWORDS
nucleosides; protecting
groups; regioselectivity; lewis
acid catalysis; DMTr-group
and DMPx-group
Introduction
The design and synthesis of chemically modified nucleosides has led to the dis-
covery of several antiviral and anticancer drugs. Often synthesis of these molecule
requires multiple protection and deprotection steps before final compound could be
assembled. The use of a protecting group triggers two extra synthetic steps which
must be clean, facile, selective and high yielding to be attractive for practical appli-
cations. Our longstanding interest in design and application of protecting groups
that are useful for nucleoside transformations has motivated us to develop new
and improved protocols.[1] Since DMTr-protecting group[2] has become one of the
workhorse for oligonucleotide synthesis and DMPx continues to generate inter-
est, we decided to further explore methodologies for their installation in an effi-
cient manner. In 2012, we reported[3] on large-scale synthesis of DMPx-OH and its
convenient installation using tri(pentafluorophenyl)borane (TPB) as a Lewis acid.
Although this study offered us a method for nucleoside protection, the high cost of
TPB discouraged further usage for scale-up. Additionally, this protocol was limited
CONTACT Shyamapada Banerjee
banerjee.s@sapalaorganics.com
Pvt. Ltd., Plot No-B & , IDA Mallapur, Hyderabad, Telangana, , India.
Research & Development, Sapala Organics
©  Taylor & Francis Group, LLC

2
S. PENJARLA ET AL.
for installation of DMPx-group. Therefore, we explored the possibility of identi-
fying another Lewis acid that is affordable and works equally well for installation
of both DMTr- and DMPx groups. Herein, we are pleased to describe our find-
ing and utility of copper(II)nitrate as a Lewis acid catalyst that enabled us not only
protection but also deprotection of both DMTr- and DMPx groups in an efficient
manner.
Results and discussion
The conventional protocol for the protection of a nucleoside with dimethoxytrityl
group involves treatment of nucleoside with DMTr-Cl in the presence of excess
pyridine serving as a base and solvent.[2] This procedure is not environmentally
friendly given the fact that pyridine is classified as a toxic solvent and used in
large excess. The high cost, storage and anhydrous handling of DMTr-Cl makes this
procedure less attractive for large-scale applications. Often times, the selectivity of
DMT-protection is not exquisite furnishing undesired bis-DMTr-protected nucle-
osides which requires chromatographic separation. These limitations of DMTr-Cl
were driving force for our current study to develop an improved protocol where
we could extend our original finding of TPB as Lewis acid catalyst.[3] The high cost
and suboptimal yield obtained with TPB[4] sparked our interest in search for a better
Lewis acid catalyst with wider utility.
In order to develop an improved protocol that is mild, eco-friendly and eco-
nomical, we sought after alternative Lewis acid catalysts.[5–8] After screening sev-
eral metal salts, we selected three nitrates (copper, nickel and silver) for the current
study. First, we tested the solubility of the Cu(NO3)2, Ni(NO3)2 and AgNO3 in var-
ious solvents and found dichloromoethane to be ideal for dissolution of the Lewis
acid and the starting materials. The evaluation of best catalyst was performed in
parallel with four nucleoside substrates 1a-4a listed in Table 1. No progress in the
reaction or product formation at room temperature was observed. Therefore, the
reaction mixture was heated to reflux until maximum conversion was accomplished
for each substrate. The results indicated that when copper(II)nitrate was employed
as the catalyst, best conversion and highest yields were obtained compared to the
use of Ni(NO3)2 and AgNO3 as catalysts. Use of 10 mol% catalyst offered most effi-
cient conversion in shortest reaction time. More importantly, the 5ꢀ-O-protection
was regioselective and all products 1b-4b were isolated as homogeneous solid after
chromatography (Scheme 1).
Next, the utility of Cu(NO3)2 as a catalyst for DMTr-protection was further tested
with five substrates 7a-11a with diverse structures furnishing 7b-11b in high yields
(71–90%; Table 2). Interestingly, the DMTr-protection of small molecules 7a-11a
was regioselective and found to be more efficient than the nucleosides substrate.
The scope and application of this reaction was further evaluated for installation of
DMPx-group.

NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
3
Table . Catalyst screening experiments for ,ꢀ-dimethoxytritylation of nucleosides.
Time
(h)
Yieldb
(%)
m.p.
(°C)
Entry

Starting Material
Producta
Catalysts
Cu(NO)
Ni(NO)
AgNO






–
1b
1a


Cu(NO)
Ni(NO)
AgNO






–
2b
2a
3a
Cu(NO)
Ni(NO)
AgNO






–
3b
4b
c
Cu(NO)
Ni(NO)
AgNO






–
4a
Reactionconditions:Substrate(.mmol),DMTrOH(.mmol)andCu(NO) (mol%)indichloromethane(mL)under
reflux condition.
aAll the products were characterized by H NMR and mass spectral analysis.
bIsolated yields after chromatography.
cThe low yield is attributed to the low solubility of 4a in dichloromethane
Scheme . Cu(NO) catalysed protection of diols with , ꢀ-dimethoxytrityl alcohol 1 and DMPx
alcohol 2.
Previously we reported[3] on DMPx-protected compounds being crystalline
in nature offering effortless isolation. Given the importance of DMPx-group, we
extended the new Cu(NO3)2 catalyzed reaction for installation of DMPx on a
variety of molecules. Gratifyingly, the reaction of electronically and structurally

4
S. PENJARLA ET AL.
Table . ,ꢀ-Dimethoxytritylation & DMPx protection of diverse substrates.
Entry
Starting Material
Time (hrs)
Producta
(Yield %)b m.p. (°C)

5a

5c


–
–

6a

6c





R = CH





R = CH, Rꢀ = DMTr 7b






… ….
–
… ….
–
… ….
–
7a
R = CH, Rꢀ = DMPx 7c
R = CH, Rꢀ = DMTr 8b
R = CH, Rꢀ = DMPx 8c
R = CHNHBz, Rꢀ = DMTr 9b
R = CHNHBz, Rꢀ = DMPx 9c
R = CH 8a
R = CHNHBz 9a




10a
10a


Rꢀ = DMTr 10b
Rꢀ = DMPx 10c


… ….
–

11a

11b

… ….

12a

12c

–


13a


13c
14c


–
14a
–
(Continued on next page)

NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
5
Table . Continued.
Entry
Starting Material
Time (hrs)
Producta
(Yield %)b m.p. (°C)




R = Bz 15a




R = Bz 15c




–
–
–
… ….
R = THP 16a
R = TBDPS 17a
R = Bn 18a
R = THP 16c
R = TBDPS 17c
R = Bn 18c

19a


19b


–
… ….

20a
20b

21a

21c

–


R = H 22a
R = Bz 23a


R = H 22c
R = Bz 23c


–
–
Reaction conditions:Substrate (. mmol), DMTrOH/DMPxOH (. mmol) and Cu(NO) ( mol%) in dichloromethane
( mL) under reflux condition.
aAll the products were characterized by H NMR and mass spectral analysis.
bIsolated yields after chromatography.
diverse aromatic compounds 5a and 6a, aliphatic compounds 7a-11a with DMPx-
OH (2) in presence of Cu(NO3)2 furnished the expected products in excellent yields
(Table 2). We were delighted to observe that compounds protected with DMPx-
group induced crystallinity whereas same compounds protetced with DMT-group
did not crystallize. The potential of synthesizing crystalline compounds via the
protection with DMPx was further explored with carbohydrates 12a-14a as sub-
strates. As expected, all three DMPx-protected 12c-14c were isolated as crystalline
products.
The compatability of these reaction conditions in presence of other sensitive
protecting group was confirmed when compounds 12a-18a and 21a-23a were
selectively converted to pixylated ethers 12c-18c and 21c-23c, repectively. It is note-
worthy that the acetonide, ether, benzyl, THP, Nap, benzoyl and TBDMS protect-
ing groups were not disturbed during protection with DMPx-group (Table 2, entry
8–15 and 21–23). Two base protected purine nucleosides 19a and 20a were also

6
S. PENJARLA ET AL.
Table . Deprotection of DMTr and DMPx ether with Cu(NO) in methanol at room temperature.
Entry
Starting Material
Productsa
Method-A Time (min)
Method-B Time (min)
(Yield %)b



2b
3b
17c
2a
3a
17a









Reaction conditions: Method-A: Substrate (. mmol), and Cu(NO) ( mol%) in Methanol ( mL); Method-B: Substrate
(. mmol), and Cu(NO). ( mol%) and triethyl silane (. mmol) in Methanol ( mL).
aAll the products were characterized by H NMR and mass spectral analysis.
bIsolated yields.
transformed successfully into 5ꢀ-O-DMTr-protected nucleosides 19b and 20b,
respectively. The stability of wide range of acid sensitive and base labile groups
demonstrated that Cu(NO3)2 catalyzed reaction is mild enough to leave the orthog-
onal protecting groups unharmed during protection of a hydroxyl group with
DMTr- or DMPx-groups.
The deprotection of DMTr- and DMPx groups is well established under acidic
conditions which invariably is a cause for depurination resulting in loss of prod-
uct yield.[9–12,14] Although deprotection of pixyl-group could be accomplished via
photolysis, it requires special equipment and may cause cross-linking in pyrimi-
dine nucleosides. Therefore, deprotection under mild conditions at room tempera-
ture would be a desirable reaction to develop. In this vein, we examined the use of
Cu(NO3)2 catalyzed deprotection in protic solvents. We were pleased to discover
that methanol as a solvent served the purpose of deprotecting both DMTr- and
DMPx-groups in an expeditious manner (Table 3). As expected, the deprotection
of DMPx-group was found to be relatively slower than the deprotection of DMTr-
group. The overall deprotection rate could be further enhanced by using triethylsi-
lane as a cation scavenger (Method B in Table 3).[13] The highly efficient protocol
may find applications toward mild deprotection of DMTr-group from an oligonu-
cleotide post DMTr-on purificaiton.
Conclusion
In summary, we have developed a practical and efficient synthetic protocol for the
selective protection of primary hydroxyl group over secondary using DMTr-OH or
DMPx-OH as protecting reagents and copper(II)nitrate as Lewis acid catalyst. The
protocol is tolerant to a variety of functional groups offering additional arsenal to the
repertoire of protecting groups. The use of more stable and easy to handle DMTr-
OH and DMPx-OH offers the convenience and advantage over conventional DMTr-
Cl and DMPx-Cl that are relatively less stable and more expensive. Therefore, this
protocol is expected to offer an economical way for synthesis of DMTr- and crys-
talline DMPx-protected molecules on large-scale. Facile and efficient deprotection
of both DMTr- and DMPx-protected nucleosides was also accomplished under mild
conditions.

NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
7
Experimental
General synthetic procedure for 4, 4ꢀ-dimethoxytrityl alcohol (1)
Anisole (21.6 g, 0.2 mol,) and benzotrichloride (19.5 g, 0.1 mol) were placed in a
three necked RB flask, equipped with a reflux condenser and mechanical stirrer,
and attached a funnel for addition of solid. The flask was cooled in an ice-bath and
aluminium chloride (10.6 g, 0.08 mol) was added in small portions to the contents of
the flask at such rate that the reaction mixture does not reflux during addition. The
addition took nearly 1.5 h. The ice–bath was removed 15 min after all the solid had
been added and the reaction was allowed to proceed without further cooling. When
the evolution of the gas subsided (nearly 2h). The reaction mixture was poured into
a mixture of crushed ice (300 g) and conc. sulphuric acid (300 ml) and stirred vigor-
ously. The two layers were separated. The aqueous layer was extracted with ethylac-
etate (1 × 100 ml). The combined organic extracts were further washed with conc.
Sulphuric acid (50 ml) and the solvent removed on rotary evaporator to give gummy
substance, which was steam distilled to remove any residual anisole. The distillate
was dissolved in hexane and dried over Na2SO4 and allow stand the solution for
crystallization to give DMT-OH 1 (27.8 g, 85%) as white color solid.
1H NMR (400 MHz, CDCl3) δ: 2.68 (s, 1H), 3.79 (s, 6H), 6.83 (d, J = 9.0 Hz, 4H),
7.17 (d, J = 9.0 Hz, 4H), 7.29 (m, 5H).
MS: 303 (M +).
General synthetic procedure for 2, 7-dimethyl-9-phenyl xanthen-9-ol (2)
To the 250 mL 3-neck RB flask charged di-p-tolylether (10 g, 50.43 mmol), ben-
zoic acid (7.39 g, 60.52 mmol) and ZnCl2 (19.73 g, 144.73 mmol) in POCl3 (15 mL)
and stirred mechanically for few minutes. Then the reaction mixture heated up to
95°C and allowed to stir for 4h. After 4h, color of the reaction mixture turned into
dark brown and unable to stir. Then the above reaction mixture cooled to 0°C and
quenched with crushed ice (40 g) while mechanically stirring. To the above reac-
tion mixture added H2O (150 ml) and allowed to stir at RT for 16h.The obtained
solid suspension filtered through Buchner funnel and the solid cake washed with
H2O (3 × 50 mL) followed by hexane (2 × 100 mL) to get crude DMPx-OH. This
crude solid re-dissolved in EtOAc (200 mL) and taken into separating flask and
washed with sat NaHCO3 (2 × 50 mL), the organic layer dried over Na2SO4 and
evaporated the solvent on rotary evaporator to get off-white color DMPx-OH 2
(10.37 g, 68%).
1H NMR (400 MHz, CDCl3) δ: 2.24 (s, 6H), 2.55 (s, 1H), 7.07 (m, 4H), 7.12 (t, J
= 0.8 Hz, 2H), 7.19 (m, 1H), 7.29 (m, 2H), 7.40 (dd, J1 = 8.3, 1.1 Hz, 2H).
MS: 285.6 (M +).
General experimental procedure for the 4, 4ꢀ-dimethoxytritylation and
pixylation of diols 1a-23a
To a mixture of diol 1a-23a (1.0 mmol) and dimethoxy triphenylmethonol 1
or 2 (1.1 mmol) in dichloromethane (10 mL), 10 mol % of Cu(NO3)2.H2O

8
S. PENJARLA ET AL.
(copper(II)nitrate monohydrate is highly oxidizing and irritant) was added and the
blue heterogeneous reaction mixture refluxed for 3–24 h. After completion of the
starting material 1a-23a, (monitored by TLC), the reaction mixture was diluted with
dichloromethane and washed with water (1 × 10 mL) and brine (1 × 10 mL). The
organic layer was dried over Na2SO4 and evaporated to get crude product. The crude
compound was purified by column chromatography (30% ethylacetate in hexane to
80% ethylacetate in hexane) to afford compound 1b-4b 17b-11b & 19b-20b or 5c-
10c, 12c-18c & 21c-23c.
,ꢀ-Dimethoxytritylation of ꢀ -O-methoxyethyl-thymidine (b)
1H NMR (400 MHz, CDCl3) δ: 1.414 (s, 3H), 3.385 (s, 3H), 3.509–3.650 (m,
5H),3.792 (s, 6H), 4.030–4.047 (m, 1H), 4.058–4.135 (m, 2H), 4.421–4.461 (m, 1H),
6.014–6.024 (d, J = 4.0 Hz, 1H), 6.826–6.849 (d, J = 9.2 Hz, 4H), 7.219–7.648 (m,
9H), 7.651 (s, 1H), 8.238 (br s, NH, 1H).
13C NMR (100 MHz, CDCl3) δ: 11.7, 29.6, 30.6, 55.2, 58.9, 62.4, 69.2, 70.2, 71.2,
82.8, 83.6, 86.8, 87.3, 110.9, 113.2, 127.1, 127.9, 128.1, 130.0, 135.2, 135.4, 135.5,
144.3, 150.2, 158.6, 163.6.
MS: 641 (M + Na).
,ꢀ-Dimethoxytritylation of ꢀdeoxy-ꢀ-fluorouridine (b)
1H NMR (400 MHz, CDCl3) δ: 2.887 (s, 1H), 2.960 (s, 1H), 3.519–3.554 (m, 1H),
3.626–3.660 (m, 1H), 3.802 (s, 6H), 4.078–4.096 (m, 1H), 4.524–4.574 (m, 1H),
4.968–5.107 (m,1H), 5.324 – 5.343 (d, J = 7.6 Hz, 1H), 6.099–6.060 (d, 1H), 6.834–
6.870 (dd, J = 2.8, 4.4 Hz, 4H), 7.235–7.390 (m, 8H), 7.905–7.927 (d, J = 8.8 Hz,
1H), 8.153 (br s, NH, 1H).
13C NMR (100MHz, CDCl3) δ: 29.6, 55.2, 60.4, 61.0, 68.8, 69.0, 82.2, 87.2, 87.4,
87.7, 87.7, 92.9, 94.7, 102.4, 113.3, 127.2, 128.0, 130.0, 130.1, 134.9, 135.1, 139.9,
144.1, 149.7, 158.7, 162.7.
MS: 549.57 (M + H).
, ꢀ-Dimethoxytritylation of N-benzoyl -ꢀ-O-methoxyethyl--methyl cytidine (b)
1H NMR (400 MHz, CDCl3) δ: 1.597 (s, 3H), 3.386 (s, 3H), 3.423–3.652 (m, 5H),
3.778 (s, 6H), 4.083–4.130 (m, 3H), 4.441–4.487 (m, 1H), 6.035–6.043 (d, J = 3.2 Hz,
1H), 6.866–6.840 (dd, J = 1.2, 9.2 Hz, 4H), 7.232–7.539 (m, 12H), 7.864 (br s, NH,
1H), 8.282–8.301 (d, J = 7.2 Hz, 2H).
13C NMR (100 MHz, CDCl3) δ: 12.8, 55.2, 58.9, 62.2, 69.1, 70.3, 71.7, 83.0, 83.6,
86.8, 87.9, 111.9, 113.2, 127.1, 128.02, 128.09, 128.1, 129.8, 130.1, 132.4, 135.2, 135.4,
136.7, 144.3, 158.6, 159.7.
MS: 722 (M + H).
, ꢀ-Dimethoxytritylation of ꢀ -O-methoxyethyl- N-benzoyl -adenosine (b)
1H NMR (400 MHz, CDCl3) δ: 3.373 (s, 3H), 3.386–3.652 (m, 5H), 3.778 (s, 6H),3.95
(m, 1H), 4.10–4.20 (m, 2H), 4.041–4.054 (t, J = 5.2 Hz, 1H), 6.200–6.208 (d, J =

NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
9
3.2 Hz, 1H), 6.589–6.609 (d, J = 8.0 Hz, 2H), 6.792–6.864 (m, 6H), 7.056–7.083
(dd, J = 5.6 Hz, 2H), 7.160–7.523 (m, 12H), 7.986 (br s, NH, 1H), 8.30 (s, 1H).
MS: 732 (M + H).
, -Dimethyl--phenyl xanthen--yl protection of benzyl alcohol (c)
1H NMR (400 MHz, CDCl3) δ: 2.206 (s, 6H), 4.060 (s, 2H), 7.061–7.081 (m, 6H),
7.148–7.185 (m, 1H), 7.246–7.252 (m, 2H), 7.284–7.321 (m, 4H), 7.444–7.463 (d,
2H).
MS: 392 (M + H).
, -Dimethyl--phenyl xanthen--yl protection of p-methoxybenzyl alcohol (c)
1HNMR (400 MHz, CDCl3) δ: 2.217 (s, 6H), 3.797 (s, 3H), 3.985 (s, 2H), 6.843–
6.865 (d, J = 8.8 Hz, 2H), 7.061–7.081 (m, 6H), 7.137–7.271 (m, 5H), 7.421–7.442
(m, 2H).
MS: 422 (M + H).
, ꢀ-Dimethoxytritylation of propane-, -diol (b)
1H NMR (400 MHz, CDCl3) δ: 1.093 (m, 3H), 2.371–2.379 (d, 1H), 2.959–3.003 (t,
1H), 3.105–3.171 (m, 1H), 3.794 (s, 6H), 3.936–4.011 (m, 1H), 6.821–6.844 (m, 4H),
7.162–7.238 (m, 1H), 7.232–7.327 (m, 6H), 7.420–7.438 (d, 2H).
13C NMR (100 MHz, CDCl3) δ: 18.9, 55.1, 67.0, 68.7, 85.9, 113.0, 126.7, 127.7,
128.0, 129.0, 130.0, 135.9, 136.0, 144.8, 158.4.
MS: 377 (M – H).
, -Dimethyl--phenyl xanthen--yl protection of Propane-, -diol (c)
1H NMR (400 MHz, CDCl3) δ: 1.04 – 1.06 (d, J = 6.8 Hz, 3H), 2.21 (s, 6H), 2.25–2.26
(d, J = 3.2 Hz, 1H), 2.80–2.84 (t, J = 8.6 Hz, 1H), 2.92–2.95 (dd, J = 2.8, 9.2 Hz, 1H),
3.90–3.95 (m, 1H), 6.94 (s, 1H), 7.04–7.08 (m, 4H), 7.16 –7.20 (m, 1H), 7.25–7.29
(m, 2H), 7.37–7.39 (m, 2H).
13C NMR (100 MHz, CDCl3) δ: 18.8, 20.8, 66.9, 68.5, 75.6, 116.0, 122.4, 126.4,
126.4, 126.5, 127.8, 129.1, 130.1, 130.15, 132.6, 132.7, 148.8, 149.3.
MS: 383 (M + Na).
, ꢀ-Dimethoxytritylation of butane-, -diol (b)
1H NMR (400 MHz, CDCl3) δ: 0.863–0.901 (t, 3H), 1.408–1.478 (m, 2H), 2.992–
3.034 (dd, 1H), 3.156–3.188 (dd, 1H), 3.670–3.721 (m,1H), 3.794 (s, 6H), 6.812–
6.850 (m, 4H), 7.160–7.234 (m, 1H), 7.272–7.328 (m, 6H), 7.420–7.441 (dd, 2H).
13C NMR (100 MHz, CDCl3) δ: 9.9, 26.3, 55.1, 67.1, 72.3, 85.9, 113.0, 126.7, 127.7,
128.1, 129.1, 130.0, 136.01, 136.09, 144.8, 158.4.
MS: 415 (M + Na).
, -Dimethyl--phenyl xanthen--yl protection of butane-, -diol (c)
1H NMR (400 MHz, CDCl3) δ: 0.82–0.86 (t, J = 7.2 Hz, 3H), 1.38–1.45 (m, 2H),
2.16–2.17 (d, J = 4.4 Hz, 1H), 2.20–2.21 (d, 6H), 2.84–2.88 (m, 1H), 2.97–3.00 (m,

10
S. PENJARLA ET AL.
1H), 3.61–3.67 (m, 1H), 6.94 (s, 2H), 7.03–7.08 (m, 4H), 7.16–7.19 (m, 1H), 7.25–
7.29 (m, 2H), 7.37 –7.38 (d, 2H).
13C NMR (100 MHz, CDCl3) δ: 9.8, 20.8, 26.2, 66.7, 72.2, 75.5, 116.6, 122.4, 126.4,
126.5, 127.8, 129.1, 130.09, 130.1, 132.6, 132.6, 132.7, 148.9, 149.
MS: 397 (M + Na)
, ꢀ-Dimethoxytritylation of N-(, -dihydroxypropyl) benzamide (b)
1H NMR (400 MHz, CDCl3) δ: 3.228–3.243 (d, 2H), 3.422–3.486 (m, 2H), 3.768 (s,
6H), 4.093–4.146 (m, 3H), 6.502–6.530 (m, 1H), 6.801–6.823 (m, 4H), 7.158–7.222
(m, 1H), 7.257–7.319 (m, 5H), 7.376–7.429 (m, 4H), 7.471–7.508 (m, 1H), 7.645–
7.667 (d, 2H).
13C NMR (100 MHz, CDCl3) δ: 14.1, 21.0, 22.6, 43.2, 55.1, 64.7, 70.1, 86.3, 113.1,
126.8, 126.9, 127.9, 128.4, 129.9, 131.5, 134.0, 135.6, 144.5, 158.5, 168.5.
MS: 496 (M – H).
, -Dimethyl--phenyl xanthen--yl protection of N-(,  dihydroxypropyl)
benzamide (c)
1H NMR (400 MHz, CDCl3) δ: 2.17–2.19 (d, 6H), 2.98–3.06 (m, 3H), 3.37–3.43 (m,
1H), 3.72 –3.78 (m, 1H), 3.95 (br s, 1H), 6.37 (br s, 1H), 6.92 (s, 2H), 7.03–7.10
(m, 4H), 7.18–7.21 (m, 1H), 7.27–7.29 (m, 2H), 7.37–7.41 (m, 4H), 7.47–7.50 (m,
1H),7.61- 7.63 (d, 2H).
13C NMR (100 MHz, CDCl3) δ: 20.7, 29.6, 43.0, 64.5, 69.9, 75.9, 116.14, 116.19,
122.0, 122.1, 126.4, 126.6, 126.9, 127.8, 128.4, 129.01, 129.1, 130.2, 131.5, 132.6,
132.5, 134.0, 148.4, 149.3, 168.5.
MS: 478.1 (M – H).
, ꢀ-Dimethoxytritylation of -(hydroxymethyl) cyclopentanol (b)
1H NMR (400 MHz, CDCl3) δ: 1.150–1.159 (m, 1H),1.081–1.159 (m, 2H), 1.734–
1.782 (m, 2H), 1.896- 1.937 (m, 1H), 2.079- 2.095 (m, 1H), 2.594–2.598 (d, 1H),
2.918–2.963 (t,1H), 3.305–3.340 (m, 1H), 3.795 (s, 6H),3.925–3.937 (d, 2H), 6.821–
6.843(d, 4H),7.296–7.318 (d, 5H), 7.403–7.423 (m, 2H).
13C NMR (100 MHz, CDCl3) δ: 21.4, 26.4, 33.6, 47.6, 55.1, 66.8, 78.1, 86.1, 113.0,
126.6, 127.7, 128.0, 129.0, 129.9, 135.9, 136.1, 144.8, 158.3.
MS: 441 (M + Na).
, -Dimethyl--phenyl xanthen--yl protection of -(hydroxymethyl) cyclopentanol
(c)
1H NMR (400 MHz, CDCl3) δ: 1.05- 1.13 (m, 1H), 1.47–1.61 (m, 2H), 1.66 –1.77
(m, 2H), 1.84–1.92 (m, 1H), 2.22- 2.23 (d, 6H), 2.82–2.86 (t, J = 9 Hz, 1H), 3.04
–3.07 (q, J = 4.8, 8.4 Hz, 1H), 3.88–3.93 (m, 1H), 6.96–7.36 (m, 11H).
13C NMR (100 MHz, CDCl3) δ: 20.8, 21.6, 26.4, 33.8, 47.7, 66.3, 78.1, 115.09,
115.9, 122.4, 122.6, 126.2, 126.4, 127.9, 129.0, 129.9, 130.0, 132.5, 132.6, 149.0, 149.3,
149.4.
MS: 423 (M + Na).

NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
11
, ꢀ-Dimethoxytritylation of tert-butyl -(,-dihydroxypropoxy)
piperidine--carboxylate (b)
1H NMR (400 MHz, CDCl3) δ: 1.254 (s, 9H), 1.472–1.516 (m, 2H), 1.758 (s, 2H),
2.423–2.437 (d, 2H), 3.047–3.111 (m, 2H), 3.161–3.28 (m, 2H), 3.422–3.576 (m,
4H), 3.655 (m, 2H), 3.789 (s, 6H), 3.880–3.920 (m, 1H), 6.814–6.836 (d, 4H), 7.211–
7.229 (m, 1H),7.284–7.323 (m, 6H),7.414–7.433 (d, 2H).
13C NMR (100 MHz, CDCl3) δ: 28.4, 30.9, 55.1, 64.1, 70.0, 75.0, 79.4, 86.0, 113.0,
126.7, 127.7, 128.1, 130.0, 135.9, 144.7, 158.4.
MS: 600 (M + Na).
,-Dimethyl--phenyl xanthen--yl protection of -O-(tert-Butyldiphenylsilyl)--C-
hydroxymethyl-,-O-isopropylidene--O-(-naphthyl- α -D-tribofuranose
(c)
1H NMR (400 MHz, CDCl3) δ: 0.93 (s, 9H), 1.01 (s, 3H), 1.24 (s, 3H), 1.87 (s, 3H),
1.20 (s, 3H), 3.25–3.28 (d, J = 10.4 Hz, 1H), 3.44–3.47 (d, J = 10 Hz, 1H), 3.54–3.57
(d, J = 11.2 Hz, 1H), 4.23–4.26 (d, J = 11.2 Hz, 1H), 4.47–4.48 (d, J = 5.2 Hz, 1H),
4.53–4.60 (m, 2H), 4.71–4.79 (d, J = 12.4 Hz, 1H), 5.77–5.78 (d, J = 3.2 Hz, 1H),
6.64 (s, 1H), 6.96–7.82 (m, 28H).
13C NMR (100 MHz, CDCl3) δ: 19.21, 20.50, 20.66, 26.18, 26.34, 26.74, 64.25,
65.67, 75.53, 75.37, 79.42, 87.91, 104.27, 113.33, 115.91, 122.47, 125.41, 125.86,
126.00, 126.06, 126.3, 127.60, 127.63, 127.69, 127.93, 128.10, 129.08, 129.63, 129.73,
132.20, 132.99, 135.24, 135.42, 135.73, 149.20, 149.44, 149.54.
MS: 284.9 (DMPx +)
,-Dimethyl--phenyl xanthen--yl protection of
(R)--((aR,R,R,aR)--methoxy-,
-dimethyltetrahydrofuro[,-d][,]dioxol--yl)ethane-, -diol (c)
1H NMR (400 MHz, CDCl3) δ: 1.33 (s, 3H), 1.54 (s, 3H), 2.21 (s, 6H), 2.37–2.38 (d,
J = 2.8 Hz, 1H), 3.02–3.08 (m, 2H), 3.26 (s, 3H), 3.64–3.67 (q, J = 13.2 Hz, 1H),
3.91–3.95 (dd, J = 3.6, 8.8 Hz, 1H), 4.05–4.09 (m, 1H), 4.59–4.61 (t, J = 4 Hz, 1H),
5.69–5.70 (d, J = 3.6 Hz, 2H), 6.95–6.97 (d, 2H), 7.02–7.07 (m, 4H), 7.15–7.19 (m,
1H), 7.24–7.28 (m, 2H), 7.37–7.40 (m, 2H).
13C NMR (100 MHz, CDCl3) δ: 20.7, 20.8, 26.4, 26.7, 57.8, 63.5, 70.2, 75.9,
77.1, 77.9, 79.8, 103.8, 112.8, 115.9, 116.0, 122.2, 122.4, 126.4, 127.7, 129.10, 129.15,
130.03, 130.09, 132.5, 132.6, 148.7, 149.2, 149.4.
MS: 541 (M + Na).
,-Dimethyl--phenyl xanthen--yl protection of ((aR,R,R,aR)--methoxy-,
-dimethyltetrahydrofuro[,-d][,]dioxol--yl)methanol (c)
1H NMR (400 MHz, CDCl3) δ: 1.28 (s, 3H), 1.41 (s, 3H), 2.19 (s, 6H), 2.96–3.00 (dd,
J = 4.4,10.4 Hz, 1H), 3.12–3.14 (m, 1H), 3.27 (s, 3H), 3.64–3.67 (dd, J = 4.4, 9.6 Hz,
1H), 3.85–3.86 (m, 1H), 4.71–4.73 (t, J = 4 Hz, 1H), 5.77–5.78 (d, J = 4.4 Hz, 1H),
6.93–6.94 (d, J = 3.6 Hz, 2H), 7.15–7.30 (m, 9H).

12
S. PENJARLA ET AL.
13C NMR (100 MHz, CDCl3) δ: 20.4, 26.4, 26.5, 57.0, 62.0, 74.9, 76.1, 76.8, 79.6,
103.8, 111.6, 116.0, 116.1, 122.2, 125.6, 126.5, 128.0, 128.4, 130.2, 132.3, 148.6, 148.7,
149.0.
MS: 511.23 (M + Na).
, -Dimethyl--phenyl xanthen--yl protection of ꢀ-deoxy ꢀ-O-benzoyl-thymidine
(c)
1H NMR (400 MHz, CDCl3) δ: 1.64 (s, 3H), 2.19 (s, 3H), 2.22 (s, 3H), 2.56–2.68 (m,
2H), 3.29–3.37 (m, 2H), 4.22–4.23 (d, J = 2 Hz, 1H), 5.61–5.6 (t, J = 3.6 Hz, 1H),
6.48–6.51 (m, 1H), 6.92 (s, 1H), 7.06–7.47 (m, 12H), 7.57–7.60 (t, 1H), 7.82 –7.83
(d, 1H), 8.00–8.02 (d, J = 7.2 Hz, 2H), 8.20 (br s, 1H).
13C NMR (100 MHz, CDCl3) δ: 11.9, 20.7, 38.4, 63.3, 75.4, 76.8, 83.7, 84.3, 111.5,
116.2, 121.4, 121.7, 126.1, 126.9, 128.1, 128.4, 128.8, 129.2, 129.6, 130.4, 130.5, 132.9,
133.2, 133.4, 135.3, 148.2, 149.1, 149.7, 150.4, 163.6, 165.6.
MS: 629 (M – H).
, -Dimethyl--phenyl xanthen--yl protection of ꢀ-deoxy ꢀ-O-THP-thymidine
(c)
1H NMR (400 MHz, CDCl3) (Diastereomericmixture) δ: 1.43–1.59 (m, 4H), 1.65
(m, 6H), 1.66–1.86 (m, 8H), 2.18 (s, 6H), 2.22 (s, 6H), 2.29–2.36 (m, 1H), 2.46–2.51
(m, 1H), 3.09–3.12 (m, 1H), 3.15 –3.18 (m, 1H), 3.24–3.31 (m, 2H), 3.34–4.63 (m,
10H), 6.30 (q, J = 6.8 Hz, 2H), 6.90 (s, 2H), 6.98–7.53 (m,22H), 8.50 (br s, 2H, NH).
13C NMR (100 MHz, CDCl3) δ: 12.0, 19.2, 20.7, 25.2, 30.5, 30.6, 62.6, 75.6, 76.2,
84.8, 97.0, 98.4, 110.9, 111.0, 126.2, 126.2,126.8,128.0,128.5, 128.6, 128.9, 130.2,
132.7, 135.5, 148.4, 149.2, 149.2, 150.1, 163.5.
MS: 609 (M – H).
, -Dimethyl--phenyl xanthen--yl protection of ꢀ-deoxy ꢀ-O-TBDPS-thymidine
(c)
1H NMR (400 MHz, CDCl3) δ: 1.03 (s, 9H), 1.57–1.58 (d, J = 0.8 Hz, 3H),1.90 (s,
3H), 2.12 (s, 3H), 2.14–2.18 (m,1H), 2.40–2.45 (m, 1H), 2.58–2.62 (m, 1H), 2.98–
3.02 (m, 1H), 3.87–3.88 (d, J = 1.6 Hz, 1H), 4.41–4.42 (d, J = 5.2 Hz, 1H), 6.49 (q,
J = 4.5 Hz, 1H), 6.75–6.77 (d, J = 9.6 Hz, 2H), 7.00- 7.44 (m, 17H), 7.44–7.68 (m,
2H), 7.68 (s, 1H), 8.50 (br s, 1H, NH).
13C NMR (100 MHz, CDCl3) δ: 11.9, 18.8, 20.5, 20.7, 26.8, 41.3, 74.4, 76.5, 85.1,
86.8, 110.8, 116.1, 121.4, 121.8, 126.1, 126.8, 127.7, 127.8, 127.9, 128.3, 128.9, 129.9,
129.9, 130.2, 130.4, 132.79, 133.0, 135.4, 135.5, 135.7, 148.3, 149.0, 149.6, 150.1,
163.62.
MS: 763 (M – H).
, -Dimethyl--phenyl xanthen--yl protection of ꢀ-deoxy ꢀ-O-Bn-thymidine (c)
1H NMR (400 MHz, CDCl3) δ: 1.707 (s, 3H), 2.172 (s, 3H), 2.213 (s, 3H), 2.263–
2.249 (m, 1H), 2.396–2.454 (m, 1H), 3.122–3.155 (m, 1H), 3.227–3.261 (m, 1H),

NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
13
3.940–3.962 (m, 1H), 4.418–4.447 (m, 1H), 5.132 (s, 2H), 6.411 (t, J = 5.7 Hz, 1H),
6.887 (s, 1H), 6.941 (s, 1H), 7.052–7.327 (m, 12H), 7.488–7.505 (d, J = 6.8 Hz, 2H),
7.638 (s, 1H).
13C NMR (100MHz,CDCl3) δ: 12.97, 20.80, 29.67, 41.13, 44.40, 63.24, 72.61,
85.40, 85.78, 110.32, 116.22, 116.32, 121.55, 121.95, 126.32, 126.91, 127.58, 128.03,
128.35, 128.60, 129.08, 129.23, 130.41, 130.53, 132.80, 132.93, 133.62, 136.90, 148.18,
149.37, 149.66, 150.94, 163.42.
MS: 617 (M + H).
, ꢀ-Dimethoxytritylation of ꢀ-O-methoxy ethyl- N-isobutyryl guanosine (MOE-G)
(b)
1H NMR (400 MHz, CDCl3) δ: 0.667- 0.684 (d, 3H), 0.878–0.895 (d, 2H), 1.243–
1.261 (m, 2H), 1.383–1.415 (m, 1H), 2.049 (s, 1H), 3.082–3.116 (m, 1H), 3.382 (s,
3H),3.449–3.765(m, 4H), 3.779(s, 6H),3.869–4.150 (m,1H),4.217(br s, 1H), 4.484–
4.496 (d, 1H), 4.954–4.983 (t, J = 6.8 Hz, 1H), 5.838–5.856 (d, 1H), 6.777–6.824
(t, J = 9.2 Hz, 4H), 7.220–7.289 (m, 3H), 7.392–7.421 (m, 5H), 7.545–7.562 (d,
2H),7.795 (s, 1H).
13C NMR (100MHz,CDCl3) δ: 18.4, 18.5, 36.0, 55.2, 59.0, 63.7, 69.3, 69.9, 71.7,
81.3, 84.4, 86.2, 86.3, 113.2, 122.4, 127.1, 128.0, 129.9, 135.6, 136.0, 136.0, 144.9,
147.0, 148.2, 155.4, 158.7, 178.3.
MS: 714 (M + H).
, ꢀ-Dimethoxytritylation of ꢀ-O-methoxy N-benzoyl –adenosine (b)
1H NMR (400 MHz, DMSO-d6) δ: 3.221–3.316 (m, 3H), 3.402 (s, 3H), 3.424 (s,
1H),3.721 (s, 6H), 4.002–4.055 (m, 1H), 4.099–4.134 (m, 1H), 4.461–4.521 (m, 1H),
4.539–4.563 (t, J = 4.8 Hz, 1H), 5.365–5.380 (d, J = 6.0 Hz, 1H), 6.183–6.208(t, J =
4.8 Hz, 1H), 6.820–6.856 (m, 4H), 7.195–7.272 (m, 7H), 7.354–7.372 (d, J = 7.2 Hz,
2H), 7.539–7.576 (m, 3H), 7.635–7.653 (m, 1H), 8.035–8.056 (m, 2H),8.620 (s, 1H),
8.699 (s, 1H).
13C NMR (100 MHz, CDCl3) δ: 14.0, 20.7, 55.0, 57.7, 59.7, 63.5, 68.9, 81.7, 53.6,
85.5, 85.9, 86.1, 113.1, 125.9, 126.6, 127.6, 127.7, 128.5, 128.7, 129.2, 129.6, 132.4,
133.2, 135.4, 135.5, 138.8, 143.2, 144.8, 150.5, 151.7, 151.9, 158.0, 165.6.
MS: 688 (M + H).
, -Dimethyl--phenyl xanthen--yl protection of ꢀ-deoxy, ꢀ-O- Bz-N Bz-cytidine
(c)
1H NMR (400 MHz, CDCl3) δ: 2.17 (s, 3H), 2.29 (s, 3H), 2.46–2.53 (m, 1H), 2.94
–2.98 (m, 1H), 3.23–3.26 (m, 1H), 3.33–3.36 (m, 1H), 4.34–4.35 (d, J = 2.4 Hz, 1H),
5.49–5.51 (t, J = 2.8 Hz, 1H), 6.92–6.94 (d, 2H), 7.07 –7.65 (m, 20H), 8.37–8.39 (d,
1H), 8.66 (br s, 1H).
13C NMR (400 MHz, CDCl3) δ: 20.6, 20.9, 39.6, 62.9, 74.7, 84.4, 87.3, 116.0, 116.2,
121.5, 121.6, 126.4, 126.9, 127.4, 127.9, 128.3, 128.9, 129.0, 129.1, 129.2, 129.6, 130.5,
132.9, 133.0, 133.1, 133.3, 144.3, 147.6, 149.4, 162.2, 165.5.
MS: 720 (M + H).

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S. PENJARLA ET AL.
,-Dimethyl--phenylxanthen--yl protection of ꢀ -deoxyuridine (c)
1H NMR (400 MHz, CDCl3) δ: 2.21–2.23 (d, 6H), 2.44–2.50 (m, 1H), 2.88 (s, 1H),
2.95 (s, 1H), 3.09–3.13 (dd, J = 3.6, 10.8 Hz, 1H), 3.22–3.25 (dd, J = 3.2, 10.4 Hz,
1H), 3.96–3.99 (m, 1H), 4.41 (s, 1H), 5.60 –5.62 (d, J = 8 Hz, 1H), 6.26–6.29 (m,
1H), 6.83–6.90 (m, 2H), 7.05 –7.42 (m, 9H), 7.84–7.86 (d, J = 8 Hz, 1H), 8.54 (br s,
1H).
13C NMR (100 MHz, CDCl3) δ: 163.4, 150.3, 149.5, 149.4, 147.7, 140.0, 132.8,
132.7, 130.4, 130.3, 129.1, 128.9, 127.9, 127.7, 127.0, 126.9, 126.4, 121.8, 121.5, 116.1,
102.1, 86.1, 85.4, 71.8, 63.0, 41.3, 36.5, 31.4, 29.6, 20.8, 20.8, 14.0.
MS: 535.1 (M + Na).
, -Dimethyl--phenyl xanthen--yl protection of ꢀ-O-Bz-ꢀ-deoxyuridine (c)
1H NMR (400 MHz, CDCl3) δ: 2.19 (s, 3H), 2.22 (s, 3H), 2.47–2.54 (m, 1H), 2.67–
2.72 (m, 1H), 3.25–3.34 (m, 2H), 4.25–3.73 (m, 1H), 4.03–4.05 (d, J = 7.2 Hz, 1H),
4.38–4.43 (m, 1H), 4.97–4.25 (d, 1H), 5.55–5.56 (d, J = 5.2 Hz,1H), 5.67–5.69 (d,
J = 8 Hz, 1H), 6.40–6.44 (t, 1H), 6.85 (s, 1H), 6.919 (s, 1H), 7.06 –7.60 (m, 12H),
7.96–8.01 (t, 3H), 9.35 (bs,1H).
13C NMR (100 MHz, CDCl3) δ: 20.7, 20.9, 38.8, 63.0, 74.7, 83.8, 85.1, 102.6, 116.1,
116.2, 121.5, 121.6, 126.4, 126.9, 127.9, 128.4, 128.8, 129.0, 129.1, 129.6, 130.4, 130.5,
132.8, 133.0, 133.4, 139.7, 147.5, 149.3, 149.5, 150.3, 163.3, 165.6.
MS: 615 (M – H).
General procedure for the deprotection of DMTr-ether and DMPx-ether (Method-A)
To a mixture of DMTr or DMPx-protected nucleosides (0.3 mmol) in MeOH (5 mL)
was added 10 mol% of Cu(NO3)2 and stirred the reaction mixture at room tem-
perature for given time (see Table 3). After completion of the reaction (monitored
by TLC), solvents were distilled out on rotary evaporator to get crude product.
The crude compound was purified by column chromatography using 60–120 sil-
ica gel and (ethyl acetate in hexane) to afford unprotected nucleosides summarized
in Table 3.
General procedure for the deprotection of DMTr-ether and DMPx-ether(Method-B)
To a mixture of DMTr or DMPx-protected nucleosides (1.0 mmol) in MeOH (5 mL)
was added, triethylsilane (3.0 mmol) and 10 mol% of Cu(NO3)2 and stirred the reac-
tion mixture at room temperature for given time (see Table 3). After completion of
the reaction (monitored by TLC), solvents were distilled out on rotary evaporator to
get crude product. The crude compound was purified by column chromatography
using 60–120 silica gel and (ethyl acetate in hexane) to afford unprotected nucleo-
sides (Table 3).
1H NMR (400 MHz, CDCl3) δ: (Compound-2a) 3.568–3.599 (m, 1H), 3.742–
3.773 (m, 1H), 3.862–3.880 (d, J = 7.2 Hz, 1H), 4.097–4.195 (m, 1H), 4.957–5.208
(m, 2H), 5.615 (t, J = 8.0Hz, 2H), 5.879–5.926 (dd, J = 1.2, 17.6 Hz, 1H), 7.905–7.926
(d, J = 8.4 Hz, 1H), 11.37 (s, 1H).

NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
15
MS: 247.15 (M + H).
1H NMR (400 MHz, CDCl3) δ: (compound-3a) 2.112 (s, 3H), 3.054 (s, 1H),
3.403 (s, 3H), 3.524–3.618 (m, 2H), 3.678–3.813 (m, 3H), 3.970–3.996 (d, J =
10.4 Hz, 2H), 4.157 (s, 1H), 4.356 (s, 1H), 4.432 (s, 1H), 5.581–5.593 (d, J = 4.8 Hz,
1H), 7.426–7.464 (m, 2H), 7.525–7.550 (m, 2H), 8.304–8.324 (d, J = 8.0 Hz, 2H),
13.326 (br s, 1H).
MS: 420 (M + H) and 418 (M – H).
1H NMR (400 MHz, CDCl3) δ: (compound-17a) 1.09 (s, 9H), 1.86 (d, J = 1.2 Hz,
3H),1.93 (dd, J = 6.5, 4.2 Hz, 1H), 2.17 (m, 1H), 2.28 (dq, J = 13.4, 3.0 Hz, 1H), 3.24
(m, 1H), 3.63 (m, 1H), 3.98 (q, J = 2.8 Hz, 1H), 4.45 (m, 1H), 6.22 (m, 1H), 7.28 (d,
J = 1.2 Hz, 1H), 7.40 (m, 4H), 7.46 (m, 2H), 7.64 (m, 4H), 8.05 (br s, 1H).
MS: 481 (M + H) and 479 (M – H).
Acknowledgments
The authors are thankful to Dr. P.Y. Reddy for his encouragement and valuable suggestions. S.P.
thanks the Director National Institute of Technology, Raipur.
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