S-Ribosylhomocysteine analogues modified at the ribosyl C-4 position

Article abstract of DOI:10.1080/17415993.2015.1137921

4-C-Alkyl/aryl-S-ribosylhomocysteine (SRH) analogues were prepared by coupling of homocysteine with 4-substituted ribofuranose derivatives. The diastereoselective incorporation of the methyl substituent into the 4 position of the ribose ring was accomplis

Full text of DOI:10.1080/17415993.2015.1137921

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
S-Ribosylhomocysteine analogues modified at the
ribosyl C-4 position
Christiane Chbib, Adam J. Sobczak, Mukesh Mudgal, Cesar Gonzalez, Daniel
Lumpuy, Justyna Nagaj, Kamila Stokowa-Soltys & Stanislaw F. Wnuk
To cite this article: Christiane Chbib, Adam J. Sobczak, Mukesh Mudgal, Cesar Gonzalez,
Daniel Lumpuy, Justyna Nagaj, Kamila Stokowa-Soltys & Stanislaw F. Wnuk (2016) S-
Ribosylhomocysteine analogues modified at the ribosyl C-4 position, Journal of Sulfur
Chemistry, 37:3, 307-327, DOI: 10.1080/17415993.2015.1137921
To link to this article: http://dx.doi.org/10.1080/17415993.2015.1137921
Published online: 24 Feb 2016.
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Date: 19 June 2016, At: 00:26

JOURNAL OF SULFUR CHEMISTRY, 2016
VOL. 37, NO. 3, 307–327
http://dx.doi.org/10.1080/17415993.2015.1137921
S-Ribosylhomocysteine analogues modified at the ribosyl C-4
position
Christiane Chbib, Adam J. Sobczak, Mukesh Mudgal, Cesar Gonzalez , Daniel
Lumpuy, Justyna Nagaj, Kamila Stokowa-Soltys and Stanislaw F. Wnuk
Department of Chemistry & Biochemistry, Florida International University, Miami, USA
ABSTRACT
ARTICLE HISTORY
Received 12 November 2015
Accepted 30 December 2015
4-C-Alkyl/aryl-S-ribosylhomocysteine (SRH) analogues were pre-
pared by coupling of homocysteine with 4-substituted ribofuranose
derivatives. The diastereoselective incorporation of the methyl sub-
stituent into the 4 position of the ribose ring was accomplished
by the addition of methylmagnesium bromide to the protected
ribitol-4-ulose yielding the 4-C-methylribitol in 85% yield as single
4R diastereomer. The 4-C hexyl, octyl, vinyl, and aryl ribitols were
prepared analogously. Chelation controlled addition of a carban-
ion to ketones from the Si-face was responsible for the observed
stereochemical outcome. Oxidation of the primary alcohol of the
4-C ribitols with catalytic amounts of tetrapropylammonium per-
ruthenate in the presence of N-methylmorpholine N-oxide produced
4-C-alkylribono-1,4-lactones in high yields. Mesylation of the lat-
ter compounds at the 5-hydroxyl position and treatment with a
protected homocysteine thiolate afforded protected 4-C-alkyl/aryl-
SRH analogues as the lactones. Reduction with lithium triethyl-
borohydride and successive global deprotections with TFA afforded
4-C-alkyl/aryl SRH analogues. These analogues might impede the
S-ribosylhomocysteinase(LuxS)-catalyzed reaction by preventing
β-elimination of a homocysteine molecule, and thus depleting the
production of quorum sensing signaling molecule AI-2.
KEYWORDS
Homocysteine; LuxS;
S-ribosylhomocysteine;
ribonolactone; C-substituted
ribose
1. Introduction
Quorum sensing (QS) is a process in which exchange of chemical signals enables bacterial
population to take control of crucial functions in united communities for enhancement of
symbiosis, virulence, and biofilm formation.[1–4] The interference in this chemical com-
munication among bacteria could result in improving our control of bacterial infection.
CONTACT Stanislaw F. Wnuk
wnuk@fiu.edu
© 2016 Informa UK Limited, trading as Taylor & Francis Group

308
C. CHBIB ET AL.
Numerous small and macromolecules that modulate QS pathways have been designed and
synthesized.[5–8] The acetylhomoserine-based isothiocyanate and haloacetamide probes,
which covalently inhibit bacterial QS [9] and probes for signaling molecules which utilize
‘click chemistry’, [10] have been developed.
The S-ribosylhomocysteinase (LuxS; EC 4.4.1.21 ) is a key enzyme in the biosynthetic
pathway for conversion of S-ribosyl-l-homocysteine (SRH, 1; Figure 1) to homocysteine
(Hcy) and 4,5-dihydroxy-2,3-pentadione (DPD), the precursor for the type II autoinducer
(AI-2) [11] which mediates the interspecies QS among bacteria (see Figure 2).[12–14]
Various SRH analogues have been designed as mechanistic probes and/or inhibitors of
the LuxS enzyme.[6] Among them, one of the most important are SRH analogues that
target mechanistic steps of the LuxS catalytic cycle by effecting the initial ring opening
step (e.g. 1-deoxy-SRH analog 2 [15] and [4-aza]-3a [16] or 4-[thio]-SRH analogs 3b
[17]; i.e. 1 → intermediate A, Figure 2) or one of the tautomerization/isomerization steps
(A → B or B → C). These included substrates lacking the enolizable hydroxyl group
at C3 (e.g. 4; X = H or OMe),[18] including mechanistically significant C3 halogenated
[3-Br or F]-SRH analogues 4.[19] Zhou and co-workers synthesized substrate analogue S-
homoribosyl-l-cysteine 5, which was designed to prevent the final mechanistic step of the
LuxS catalytic cycle.[15] Moreover, brominated furanone derivatives were found to modify
LuxS selectively leading to the covalent inhibition.[20]
The substitution of hydrogen at C4 by an alkyl or aryl group in SRH (e.g. 18) should
impede the LuxS-catalyzed reaction by preventing β-elimination of a homocysteine
molecule (i.e. C → D) since abstraction of the C4-proton by a general base (e.g. Glu158)
from the intermediate C, when R = alkyl/aryl, will be disallowed (Figure 2). Consequently,
the formation of DPD necessary for the production of AI-2 would be depleted with
4-C-alkyl-SRH analogues.
Since LuxS forms a dimer it is possible that the size and chemical nature of the group
incorporated at C4 of the ribose ring might also play an additional role in inhibiting dimer-
ization. Recently, the SRH analogues having the sterically demanding alkyl or aryl group at
the Hcy fragment of the SRH have been designed and were attempted to be synthesized.[21]
These analogues were thought to be able to bind to one monomer of the LuxS protein while
blocking the correct association of the second monomer, possibly interfering with dimer-
ization interfaces.[21–23] In theory, for example, the longer the alkyl chain incorporated
at the C4 position in analogs 18, the more potent the inhibition of dimerization of LuxS
might be observed since the inhibitor can reach both homodimer parts of the protein. The
inhibitor might also block one monomer leading to the alteration of the activity and as a
consequence conformational changes of the second monomer. Herein, we report synthesis
Figure 1. Selected LuxS inhibitors.

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309
Figure 2. A plausible inhibition of LuxS enzyme by 4-C substituted SRH analogues.
of [4-alkyl/aryl]-SRH analogues which would deplete the production of AI-2 by preventing
elimination of Hcy and could also act as dimerization inhibitors.
2. Results and discussion
The 4-C-alkyl/aryl-S-ribosylhomocysteine analogues were prepared by coupling of the
homocysteine with the 4-C-substituted ribofuranose derivatives. The 4-C-substituted
riboses can be prepared either by manipulation of natural carbohydrates [24] or the
chemoenzymatic strategy from non-sugar precursors.[25,26] From the method available,
we chose Maddaford’s method for diastereoselective incorporation of the alkyl substituent
into the 4 position of the D-ribose ring by the addition of Grignard reagents to 4-ulose.[24]
Reduction of the protected ribose 6 with NaBH4 provided the acyclic ribitol 7 (Scheme 1).
Regioselective silylation of the primary hydroxyl with TBDMSCl and subsequent Dess-
Martin or Collins oxidation of the secondary hydroxyl in 8 yielded ketone 9. The overall
yield for the conversion of the ribose to the ribitol-4-ulose 9 [27] was 75% (5 steps).
Treatment of ketone 9 with methylmagnesium bromide at −78°C produced the 4-
C-methylribitol 4R-10a in 85% yield as a single isomer after purification by silica gel
chromatography. The addition of the hexylmagnesium bromide or octylmagnesium bro-
mide to ketone 9 gave the corresponding 4-C-hexyl and 4-C-octyl ribitols 10b and 10c in
74% and 69% isolated yields, respectively. The 4-C-vinyl ribitol 10d (61%) and 4-C-aryl
ribitol 10e (96%) were prepared analogously. The Grignard reagent addition to the ribitol-
4-ulose 9, which is an α-alkoxy ketone, is proposed to proceed via a 5-membered ring

310
C. CHBIB ET AL.
Scheme 1. Reagents and conditions: (a) NaBH4/EtOH/H2O; (b) TBDMSCI/imidazole/CH2Cl2/16 h;
(c) Dess-Martin (3 h) or Collins (1 h) reagents; (d) RMgX/Et2O/−78°C; (e) TBAF/THF; (f)
TPAP/NMO/CH2Cl2/6 h; (g) TFA/CH2Cl2/r.t.; and (h) LiEt3BH/CH2Cl2/0°C/0.5 h.
chelate [28] with the complexation of the metal with the carbonyl group and the α-alkoxy
group at C3 allowing transfer of the alkanide carbanion in the anti-fashion (Si-face) to the
α-alkoxy group at C3.[24,29]
Treatment of the 4-C-methylribitol 10a with TBAF (0°C/30 min) effected desilylation
to give ribitol 11a (78%). Analogous deprotection of 10b–e produced the 4-C-substituted
ribitols 11b–e (75–87%) with a primary hydroxyl group at C1 and a tertiary hydroxyl
group at C4. For the ring closure, we elected the oxidation of the primary alcohol
at C1 to the carboxylic acid with the concomitant ring closure to the corresponding
ribono-1,4-lactones,[30,31] since such an approach would provide convenient precursors
for the synthesis of both 4-C-substituted SRH lactones [32] and, after reduction, 4-C-
alkyl/aryl SRH analogues. Thus, oxidation (6 h) of the 11a with a catalytic amount of
tetrapropylammonium perruthenate (TPAP) in the presence of a stoichiometric amount of
N-methylmorpholine N-oxide (NMO) [33,34] gave the corresponding 4-C-methylribono-
1,4-lactone 12a (80%). The formation of lactone was supported by the disappearance of
the signals for H1 and H1ꢀ protons (1H NMR) and the appearance of a peak at 172.1 ppm
for the carbonyl carbon at C1 (13C NMR). Oxidation of 4-C-hexyl and 4-C-octyl ribitols
11b or 11c with TPAP/NMO also proceeded smoothly to give the 4-C-hexyl- and 4-C-
octylribonolactones12b and 12c (95%). The longer reaction time (e.g. 14 h), especially with

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311
substrates with long alkyl chain (e.g. 11c), led to the formation of by-product(s) (∼30%).
The 4-C-vinyl 12d and 4-C-aryl 12e lactones were obtained analogously by the oxidation
of 11d and 11e, respectively.
Detritylation of 12a (6 h, rt) with TFA/CH2Cl2 gave 13a (66%). Analogous treatment of
the hexyl 12b and octyl 12c with TFA (5 h, rt) gave ribono-1,4-lactones 13b and 13c in 80%
and 75% yields, respectively. The longer reaction time should be avoided since the forma-
tion of by-product(s) was observed during detritylation of 12b to 13b when the reaction
was carried out for 16 h.[35] Treatment of the vinyl analogue 12d with TFA (5 h, rt) also
gave detritylated ribonolactone 13d but only in 35% yield after purification on silica gel
column chromatography. Similarly, 4-C-aryl analogues 12e were converted to 13e (70%).
Careful reduction of the protected 4-C-hexyl ribonolactone 12b with LiEtBH3 (−20°C,
30 min) gave lactol 14b as an anomeric mixture (α/β, 1:3) in 54% yield after column chro-
matography. The chemical shifts for the anomeric protons and the magnitude of vicinal
3JH1–H2 coupling constants were diagnostic [36,37] for the determination of the composi-
tion of α/β anomers. The anomeric proton for α-isomer [5.61 ppm (dd, J = 4.2, 11.5 Hz)]
appeared as doublet of doublets with splitting to H2 and OH group, while H1 proton for
β-anomer appears upfield as a doublet [5.15 (d, J = 8.4 Hz)].
Next, the coupling of the selected ribono-1,4-lactones 13 with homocysteine was exam-
ined. Thus, treatment of 13b, 13c, or 13e with methylsulfonyl chloride gave the primary 5-
O-mesyl derivatives 15b, 15c, and 15e (60–83%). From different approaches [13,15,38–40]
tested for the nucleophilic displacement of the mesylate in 15 with homocysteine thiolates,
we found that reactions with the (N-Boc, COOtBu) protected homocysteine, generated
in situ by the reduction of the corresponding homocystine [13] with water-extractable
tris(2-carboxyethyl)phosphine [18] gave the best results. Thus, treatment of the 15b with
homocysteine thiolate (3 equiv) generated from BocNHCH(CH2CH2SH)CO2t-Bu/LDA
afforded protected 4-C-hexyl-SRH lactone 16b (65%, Scheme 2). Analogous coupling of
15c with Hcy gave 16c, contaminated with the protected Hcy substrate (∼1:1), which was
directly used in the subsequent deprotection step. 4-C-Aryl mesylate 15e was coupled with
homocysteine thiolate to give 16e (48%). It is noteworthy to add that displacement of the
Scheme 2. MsCl/TEA/CH2Cl2; (b) BocNHCH(CH2CH2SH)CO2t-Bu/LDA/DMF; (c) TFA/H2O; and (d)
LiEt3BH/THF.

312
C. CHBIB ET AL.
primary mesylate (or tosylate) from the highly branching ribonolactones 15 having trisub-
stituted carbon (C4) at the adjacent position needs to be carried out with great caution to
avoid the formation of by-products. The structure of one such by-product isolated from the
reaction of 15c with Hcy was tentatively assigned as the 2,3-O-isopropylidene-4-C-octyl-
D-ribono-1,5-lactone (see note under the experimental procedure for 17c) based on the
spectroscopic analysis (1H and 13C NMR and HRMS) and by comparison with the similar
ribono-1,5-lactones.[41]
Treatment of 16b with TFA effected global removal of the N-Boc, acetonide and t-
butyl ester protecting groups to give 4-C-hexyl-SRH lactone 17b in 55% yield after HPLC
purification. Analogous treatment of the crude 16c with TFA and purification of the result-
ing mixture on the Sep-Pak column gave 4-C-octyl-SRH lactone 17c in 21% overall yield
from 15c. Deprotection of 16e gave 4-C-(4-methoxyphenyl)-SRH lactone 17e (75%).
Synthesis of the somehow unstable 4-C-alkyl/aryl-SRH derivatives 19 was accomplished
by the reduction of either protected 16 or deprotected 17 lactones with lithium triethyl-
borohydride. Thus, treatment of 17c with LiEt3BH/THF (2 equiv.) in CH2Cl2 at −20°C
effected reduction of the lactone yielding 4-C-octyl SRH 19c (α/β, ∼1:3; 60%). Alterna-
tively, reduction of the protected 4-C-hexyl-SRH lactone 16b with LiEt3BH followed by
deprotection of the resulting 18b with TFA and TFA/H2O afforded 4-C-hexyl-SRH 19b
(α/β, 1:9; 75%). Similarly, subjection of 16e to the reduction and deprotection sequence
afforded 4-C-(4-methoxyphenyl)-SRH 19e (α/β, 1:9; 77%).
3. Conclusion
We have developed synthesis of S-ribosylhomocysteine analogues substituted at the ribosyl
C-4 position with the alkyl or aryl group. The critical steps in this multistep synthesis start-
ing from ribose were (i) diasteroselective addition of the alkyl/aryl-magnesium bromides
to protected ribitol-4-ulose to produce the 4-C-alky/aryl-ribitols in high yields as single
4R diastereomers, (ii) oxidation of the primary alcohol at C1 of the 4-C substituted ribitols
with the catalytic amounts of tetrapropylammonium perruthenate in the presence of a sto-
ichiometric amount of N-methylmorpholine N-oxide to give 4-C-alkyl/aryl-ribono-1,4-
lactones in good yields, (iii) displacement of 5-mesylate with the protected homocysteine
thiolate to afford protected 4-C-alkyl/aryl-SRH analogues with a lactone carbonyl at the
C1 position, and (iv) reduction with lithium triethylborohydride and successive global
deprotections with TFA to give 4-C-alkyl/aryl-SRH analogues. Enzymatic and biological
properties of these novel analogues of SRH will be published elsewhere.
4. Experimental section
4.1. General procedures
1
The H (400 or 600 MHz) and 13C (100 MHz) NMR spectra were determined with
solutions in CDCl3 unless otherwise noted. Mass spectra (MS) and HRMS were
obtained in the AP-ESI or TOF-ESI mode. TLC was performed with Merck kiesel-
gel 60-F254 sheets, products were detected with 254 nm light or by visualization with
the Ce(SO4)2/(NH4)6Mo7O24·4H2O/H2SO4/H2O reagent. Merck kieselgel 60 (230–400
mesh) was used for column chromatography. Final products were purified using the HPLC

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313
[XTerra preparative RP18 OBD column (5 μm 19 × 150 mm) with a gradient program using
CH3CN/H2O as a mobile phase] or Sep-Pak cartridge (C18 classic column) using water
and ethanol as eluting system. Reagent grade chemicals were used, and solvents were dried
by reflux over and distillation from CaH2 (except for THF/potassium) under argon. The
4-C-substituted SRH analogues need to be handled with care and stored in a refrigerator
(∼4°C) in solid or dried oil state.
4.2. 2,3-O-Isopropylidene-5-O-tritylribitol (7)
NaBH4 (91 mg, 2.4 mmol) was added to a stirred solution of 6 [42] (865 mg, 2.0 mmol)
in EtOH (20 mL) at 0°C (ice bath) under N2 atmosphere. After 1 h, the reaction mix-
ture was partitioned between NaHCO3/H2O and EtOAc. The organic layer was dried over
anhydrous MgSO4 and evaporated. The residue was column chromatographed (30% hex-
ane/EtOAc) to give 7[24] (807 mg, 93%): 1H NMR δ 1.35 (s, 3H, CH3), 1.37 (s, 3H, CH3),
2.96 (d, J = 3.6 Hz, 1H, OH), 3.08 (dd, J = 5.0, 8.4 Hz, 1H, H1), 3.34 (dd, J = 6.9, 9.8 Hz,
1H, H5), 3.50 (dd, J = 2.9, 9.8 Hz, 1H, H5ꢀ), 3.75–3.81 (m, 1H, H1ꢀ), 3.83–3.91 (m, 1H,
H4), 4.10–4.17 (m, 1H, H2), 4.33–4.40 (m, 1H, H3), 7.25–7.38 (m, 15H, Ar); MS (ESI+)
m/z 457 (M+Na+).
4.3. 1-O-tert-Butyldimethysilyl-2,3-O-isopropylidene-5-O-tritylribitol (8)
TBDMSCl (302 mg, 2.0 mmol) and imidazole (204 mg, 3.0 mmol) were added to a solution
of 7 (652 mg, 1.5 mmol) in DMF (10 mL) at room temperature and stirring was con-
tinued for 72 h. The volatiles were evaporated and the residue was partitioned between
saturated NH4Cl/H2O and EtOAc. The separated organic layer was then washed with
NaHCO3/H2O, dried over Mg2SO4, evaporated and the resulting residue was column
chromatographed (50% hexane/EtOAc) to give 8 [24] (666 mg, 81%) as an amorphous
white powder: 1H NMR δ 0.08 (s, 6H, SiMe2), 0.81 (s, 9H, t-Bu), 1.35 (s, 3H, CH3), 1.37 (s,
3H, CH3), 3.20 (dd, J = 5.3, 9.7 Hz, 1H, H5), 3.25 (dd, J = 2.8, 9.7 Hz, 1H, H5’), 3.49 (dd,
J = 4.1, 10.6 Hz, 1H, H1), 3.68 (dd, J = 8.7, 10.5 Hz, 1H, H1’), 3.79–3.81 (m, 1H, H4),
4.13–4.15 (m, 1H, H2), 4.22 (dd, J = 5.5, 9.2 Hz, 1H, H3), 7.25–7.38 (m, 15H, Ar); MS
(ESI+) m/z 571 (M+Na+).
4.4. 1-O-tert-Butyldimethysilyl-2,3-O-isopropylidene-5-O-tritylribitol-4-ulose (9)
Method A. The Dess-Martin reagent (2.35 mL of 15 wt% solution/CH2Cl2; 381 mg,
0.9 mmol) was added to a solution of 8 (330 mg, 0.6 mmol) in CH2Cl2 (8 mL) at room
temperature and stirred for 3 h. The reaction mixture was partitioned between saturated
NaHCO3 (10 mL)/dilute Na2S2O3 (5 mL) and CH2Cl2 (15 mL). The organic layer was
dried over anhydrous MgSO4 and evaporated. The residue was column chromatographed
(85% hexane/EtOAc) to give 9 [24] (300 mg, 91%) as an oil: 1H NMR δ 0.08 (s, 6H, SiMe2),
0.81 (s, 9H, t-Bu), 1.35 (s, 3H, CH3), 1.37 (s, 3H, CH3), 3.68 (dd, J = 4.2, 11.2 Hz, 1H, H1),
3.76 (dd, J = 4.0, 11.2 Hz, 1H, H1’), 4.04 (d, J = 17.7 Hz, 1H, H5), 4.20 (d, J = 17.8 Hz,
1H, H5’), 4.51–4.53 (m, 1H, H2), 4.71 (d, J = 7.8 Hz, 1H, H3), 7.25–7.38 (m, 15H, Ar);
MS (ESI+) m/z 569 (M+Na+).

314
C. CHBIB ET AL.
Method B. A freshly prepared solution of the Collins reagent [CrO3 (144 mg,
1.44 mmol), pyridine (0.116 mL, 114 mg, 1.44 mmol), and Ac2O (0.272 mL, 294 mg,
2.88 mmol) in CH2Cl2 (2 mL)] was added to a stirred solution of 8 (200 mg, 0.36 mmol)
in CH2Cl2 (8 mL) at ambient temperature. The resulting mixture was stirred for 1 h and
was immediately column chromatographed (EtOAc) to give 9 (185 mg, 93%) with spectra
properties as above.
4.5. General procedure for the synthesis of 4-C-substituted ribitols 10
RMgBr reagent (0.75 mmol) was added to a stirred solution of 9 (205 mg, 0.375 mmol) in
anhydrous THF (5 mL) at −78°C under N2 atmosphere. After 15 min, the reaction mixture
was allowed to warm up to ambient temperature and was kept stirring for 2 h. The reaction
was then quenched by the addition of MeOH (1 mL) and diluted with EtOAc (15 mL). The
resulting mixture was washed with 0.1 N HCl and the organic layer dried over anhydrous
MgSO4. Volatiles were evaporated and the crude residue was then purified by flash column
chromatography (90% hexane/EtOAc).
4.5.1. 1-O-tert-Butyldimethysilyl-2,3-O-isopropylidene-4-C-methyl-5-O-tritylribitol
(10a)
Treatment of 9 (205 mg, 0.375 mmol) with MeMgBr (1 M/THF, 0.75 mL, 0.75 mmol), using
1
the procedure reported in Section 4.5, gave 10a [24] (180 mg, 85%) as an clear oil: H
NMR δ 0.08 (s, 6H, SiMe2), 0.81 (s, 9H, t-Bu), 1.35 (s, 3H, CH3), 1.40 (s, 6H, 2 × CH3),
3.01 (d, J = 8.7 Hz, 1H, H5), 3.12 (d, J = 8.7 Hz, 1H, H5’), 3.25 (dd, J = 3.8, 10.9 Hz, 1H,
H1), 3.70 (dd, J = 3.8, 10.9 Hz, 1H, H1’), 3.90–3.95 (m, 1H, H2), 4.40 (d, J = 5.5 Hz, 1H,
H3), 7.25–7.38 (m, 15H, Ar); HRMS calcd for C34H46O5SiNa+ [M+Na]+ 585.3007, found
585.3009.
4.5.2. 1-O-tert-Butyldimethysilyl-4-C-hexyl-2,3-O-isopropylidene-5-O-tritylribitol
(10b)
Treatment of 9 (165 mg, 0.30 mmol) with n-C6H13MgBr (0.8 M/THF; 0.75 mL, 0.6 mmol),
using the procedure reported in Section 4.5 (flash column chromatography; 80% hex-
ane/EtOAc), gave 10b (140 mg, 74%) as a clear oil: 1H NMR δ 0.08 (s, 6H, SiMe2), 0.81
(s, 9H, t-Bu), 0.89 (t, J = 6.6 Hz, 3H, H6a ), 1.30–1.40 (m, 8H, H2a–H5a), 1.40 (s, 3H,
CH3), 1.50 (s, 3H, CH3), 1.50–1.60 (m, 2H, H1a), 3.06 (d, J = 8.9 Hz, 1H, H5), 3.22 (d,
J = 8.9 Hz, 1H, H5’), 3.28 (dd, J = 3.8, 11.1 Hz, 1H, H1), 3.72 (dd, J = 7.6, 11.0 Hz, 1H,
H1’), 3.80–3.85 (m, 1H, H2), 4.40 (d, J = 5.2 Hz, 1H, H3), 7.25–7.38 (m, 15H, Ar); HRMS
calcd for C39H56O5SiNa+ [M+Na]+ 655.3789, found 655.3799.
4.5.3. 1-O-tert-Butyldimethysilyl-2,3-O-isopropylidene-4-C-octyl-5-O-tritylribitol
(10c)
Treatment of 9 (480 mg, 0.87 mmol) with n-C8H17MgBr (2 M/THF; 0.87 mL, 1.74 mmol),
1
using the procedure reported in Section 4.5, gave 10c (402 mg, 69%) as a clear oil: H
NMR δ 0.08 (s, 6H, SiMe2), 0.81 (s, 9H, t-Bu), 0.89 (t, J = 6.6 Hz, 3H, H8a), 1.28–1.30
(m, 12H, H2a–H7a), 1.38 (s, 3H, CH3), 1.42 (s, 3H, CH3), 1.50–1.60 (m, 2H, H1a), 3.05
(d, J = 8.9 Hz, 1H, H5), 3.21 (d, J = 8.9 Hz, 1H, H5’), 3.26 (dd, J = 3.8, 11.0 Hz, 1H,
H1), 3.70 (dd, J = 3.9, 11.0 Hz, 1H, H1’), 3.80–3.85 (m, 1H, H2), 4.40 (d, J = 5.2 Hz, 1H,

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315
H3), 7.25–7.38 (m, 15H, Ar); HRMS calcd for C41H60O5SiNa+ [M+Na]+ 683.4102, found
683.4128.
4.5.4. 1-O-tert-Butyldimethysilyl-2,3-O-isopropylidene-5-O-trityl-4-C-vinylribitol
(10d)
Treatment of 9 (120 mg, 0.21 mmol) with vinyl-MgBr (1 M/THF; 0.42 mL, 0.42 mmol),
using the procedure reported in Section 4.5, gave 10d (78 mg, 61%) as a clear oil: 1H NMR
δ 0.08 (s, 6H, SiMe2), 0.81 (s, 9H, t-Bu), 1.35 (s, 3H, CH3), 1.37 (s, 3H, CH3), 2.92 (d,
J = 9.0 Hz, 1H, H5), 3.12 (d, J = 9.0 Hz, 1H, H5’), 3.42 (dd, J = 4.5, 10.7 Hz, 1H, H1),
3.80 (dd, J = 8.5, 10.7 Hz, 1H, H1’), 4.00–4.13 (m, 1H, H2), 4.69 (d, J = 6.1 Hz, 1H, H3),
=
=
5.16 (dd, J = 1.7, 10.9 Hz, 1H, CH CHH), 5.40 (dd, J = 1.8, 17.4 Hz, 1H, CH CHH),
6.20 (dd, J = 10.9, 17.4 Hz, 1H, CH CHH), 7.25–7.38 (m, 15H, Ar); 13C NMR δ −5.40
=
(SiMe2), 21.02 and 25.29 (CMe2), 25.77 (SiCMe3), 31.58 (SiCMe3), 60.47 (CPh3), 61.98
(C1), 69.13 (C5), 74.87 (C4), 78.15 (C2), 78.45 (C3), 107.87 (CH CH2), 114.84 (CMe2),
=
=
126.91 and 127.71 and 128.87 and 143.40 (Ar), 146.89 (CH CH2); HRMS calcd for
C35H46O5SiNa+ [M+Na]+ 597.3007; found 597.3006.
4.5.5. 1-O-tert-Butyldimethysilyl-2,3-O-isopropylidene-4-C-4-methoxyphenyl-5-O-
tritylribitol (10e)
Treatment of 9 (165 mg, 0.30 mmol) with 4-MeOC6H4MgBr (1 M/THF; 0.60 mL,
0.60 mmol), using the procedure reported in Section 4.5, gave 10e (190 mg, 96%) as a
clear oil:1H NMR δ 0.08 (s, 6H, SiMe2), 0.81 (s, 9H, t-Bu), 1.35 (s, 3H, CH3), 1.37 (s,
3H, CH3), 3.01 (d, J = 9.1 Hz, 1H, H5), 3.15 (d, J = 9.1 Hz, 1H, H5’), 3.41 (dd, J = 4.5,
10.8 Hz, 1H, H1), 3.80 (s, 3H, CH3O), 3.85 (dd, J = 4.5, 10.8 Hz, 1H, H1’), 4.19–4.22 (m,
1H, H2), 5.05 (d, J = 6.4 Hz, 1H, H3), 6.85 (d, J = 6.9 Hz, 2H, Ar), 7.25–7.38 (m, 15H,
Ar), 7.61 (d, J = 8.9 Hz, 2H, Ar); HRMS calcd for C40H50O6SiNa+ [M+Na]+ 677.3269,
found 677.32567.
4.6. General procedure for desilylation of 4-C-substituted ribitols
TBAF (1 M/THF; 0.4 mL, 0.4 mmol) was added to a stirred solution of 10 (0.33 mmol)
in THF (6 mL) at 0°C (ice bath). After 1 h, the volatiles were evaporated and the result-
ing residue was washed with NaHCO3/H2O and extracted with EtOAc. The organic layer
was then dried over Mg2SO4 and evaporated to give the crude residue which was column
chromatographed (80 → 70% hexane/EtOAc).
4.6.1. 2,3-O-Isopropylidene-4-C-methyl-5-O-tritylribitol (11a)
Treatment of 10a (189 mg, 0.33 mmol) with TBAF, using the procedure reported in
1
Section 4.6, gave 11a (118 mg, 78%): H NMR δ 1.35 (s, 3H, CH3), 1.40 (s, 3H, CH3),
1.49 (s, 3H, CH3), 3.05 (d, J = 9.0 Hz, 1H, H5), 3.32 (d, J = 9.0 Hz, 1H, H5’), 3.58 (dd,
J = 5.2, 12.0 Hz, 1H, H1), 3.75 (dd, J = 5.5, 12 Hz, 1H, H1’), 4.10–4.20 (m, 1H, H2), 4.30
(d, J = 6.2 Hz, 1H, H3), 7.25–7.38 (m, 15H, Ar); 13C NMR δ 14.21 (C1a), 25.17 and 27.28
(CMe2), 60.42 (C5), 61.43 (C1), 67.95 (CPh3), 68.38 (C4), 77.61 (C2), 79.10 (C3), 107.67
(CMe2), 127.27 and 127.97 and 128.62 and 143.43 (Ar); HRMS calcd for C28H32O5Na+
[M+Na]+ 471.2142; found 471.2158.

316
C. CHBIB ET AL.
4.6.2. 2,3-O-Isopropylidene-4-C-hexyl-5-O-tritylribitol (11b)
Treatment of 10b (280 mg, 0.44 mmol) with TBAF, using the procedure reported in Section
1
4.6, gave 11b (145 mg, 87%) as a viscous oil: H NMR δ 0.85 (t, J = 6.6 Hz, 3H, H6a),
1.30–1.40 (m, 8H, H2a–H5a), 1.25 (s, 3H, CH3), 1.40 (s, 3H, CH3), 1.50–1.60 (m, 2H, H1a),
2.91 (d, J = 9.3 Hz, 1H, H5), 3.20 (d, J = 9.3 Hz, 1H, H5’), 3.30 (dd, J = 5.0, 12.2 Hz, 1H,
H1), 3.40 (dd, J = 5.0, 12.0 Hz, 1H, H1’), 3.80 (q, J = 5.8 Hz, 1H, H2), 4.15 (d, J = 5.8 Hz,
1H, H3), 7.25–7.38 (m, 15H, Ar);13C NMR δ 14.14 (C6a), 22.61, 23.06, 29.74, 31.83
(C2a–C5a), 25.45 and 27.57 (CMe2), 36.05 (C1a), 61.88 (C1), 64.11 (C5), 74.35 (CPh3),
77.55 (C4), 79.14 (C2), 86.92 (C3), 107.21 (CMe2), 127.31 and 127.96 and 128.65 and
143.37 (Ar); HRMS calcd for C33H42O5Na+ [M+Na]+ 541.2924; found 541.2924.
4.6.3. 2,3-O-Isopropylidene-4-C-octyl-5-O-tritylribitol (11c)
Treatment of 10c (350 mg, 0.52 mmol) with TBAF, using the procedure reported in Section
1
4.6, gave 11c (200 mg, 84%) as a viscous oil. H NMR δ 0.80 (t, J = 6.6 Hz, 3H, H8a),
1.20–1.30 (m, 12H, H2a–H7a), 1.29 (s, 3H, CH3), 1.40 (s, CH3), 1.50–1.60 (m, 2H, H1a),
2.95 (d, J = 9.4 Hz, 1H, H5), 3.25 (d, J = 9.3 Hz, 1H, H5’), 3.35 (dd, J = 4.92, 12.2 Hz,
1H, H1), 3.45 ( dd, J = 5.4, 12.2 Hz, 1H, H1’), 3.87–3.94 (m, 1H, H2), 4.10 (d, J = 5.8 Hz,
1H, H3), 7.25–7.38 (m, 15H, Ar); 13C NMR δ 14.24 (C8a), 22.79, 23.17, 29.35, 29.68,
30.18, 32.00 (C2a–C7a), 25.54 and 27.65 (CMe2), 36.13 (C1a), 61.94 (C1), 64.27 (C5),
74.41 (CPh3), 77.65 (C4), 79.28 (C2), 87.00 (C3), 107.27 (CMe2), 127.37, 128.03, 128.75
and 143.49 (Ar); HRMS calcd for C35H46O5Na+ [M+Na]+ 569.3237; found 569.3237.
4.6.4. 2,3-O-Isopropylidene-4-C-vinyl-5-O-tritylribitol (11d)
Treatment of 10d (200 mg, 0.34 mmol) with TBAF, using the procedure reported in Section
1
4.6, gave 11d (124 mg, 77%) as a viscous oil: H NMR δ 1.35 (s, 3H, CH3), 1.37 (s, 3H,
CH3), 3.38 (d, J = 11.2 Hz, 1H, H5), 3.54 (d, J = 11.2 Hz, 1H, H5’), 3.58 (dd, J = 5.1,
11.3 Hz, 1H, H1), 3.90 (d, J = 8.6, 11.3 Hz, 1H, H1’), 4.25–4.30 (m, 1H, H2), 4.32 (d,
=
J = 6.5 Hz, 1H, H3), 5.20 (dd, J = 1.2, 11.0 Hz, 1H, CH CHH), 5.40 (dd, J = 1.5, 17.6 Hz,
=
=
1H, CH CHH), 6.20 (dd, J = 11.0, 17.5 Hz, 1H, CH CHH), 7.25–7.38 (m, 15H, Ar);
13C NMR δ 24.65 and 27.07 (CMe2), 60.29 (CPh3), 60.62 (C1), 68.07 (C5), 77.90 (C2),
=
78.10 (C4), 82.01 (C3), 115.48 (CMe2), 116.03 (CH CH2), 126.82 +and 127.65+and 128.75
=
and 143.28 (Ar), 146.88 (CH CH2); HRMS calcd for C29H32O5Na [M+Na] 483.2142,
found 483.2131.
4.6.5. 2,3-O-Isopropylidene-4-C-4-methoxyphenyl-5-O-tritylribitol (11e)
Treatment of 10e (190 mg, 0.29 mmol) with TBAF, using the procedure reported in Section
1
4.6, gave 11e (117 mg, 75%) as a viscous oil: H NMR δ 1.35 (s, 3H, CH3), 1.37 (s, 3H,
CH3), 3.01 (dd, J = 6.0, 11.7 Hz, 1H, H1), 3.03 (d, J = 9.0 Hz, 1H, H5), 3.23 (dd, J = 6.0,
11.7 Hz, 1H, H1’), 3.45 (d, J = 9.0 Hz, 1H, H5’), 3.72 (s, 3H, CH3O), 4.19–4.22 (m, 1H,
H2), 4.75 (d, J = 6.6 Hz, 1H, H3), 6.85 (d, J = 6.9 Hz, 2H, Ar), 7.61 (d, J = 8.9 Hz, 2H,
Ar), 7.25–7.38 (m, 15H, Ar); 13C NMR δ 24.58 and 27.02 (CMe2), 55.19 (CH3O), 60.04
(CPh3), 61.28 (C1), 69.73 (C5), 78.08 (C2), 79.05 (C3), 82.02 (C4), 113.48 (CMe2), 127.25,
127.37, 127.92, 159.10 (Ar), 128.57 and 129.68 and 132.91 and 146.88 (Ar); HRMS calcd
for C34H36O6Na+ [M+Na]+ 563.2404; found 563.2386.

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4.7. General procedure for the synthesis of 4-C-substituted ribono-1,4-lactones 12
N-Methylmorpholine N-oxide (NMO; 50 mg, 0.42 mmol) and tetrapropylammonium per-
ruthenate (TPAP; 1 mg, 0.002 mmol) were added to a stirred solution of 11 (0.11 mmol)
in CH2Cl2 (3.5 mL) at ambient temperature under N2 atmosphere. After 6 h, the reaction
mixture was filtered off and the filtrate was dried over MgSO4 and evaporated. The residue
was purified by flash column chromatography (75 → 50% hexane/EtOAc) to give 12.
Note: Treatment of 11 with NMO and TPAP, as described above, in the presence of 4 Å
molecular sieves (100 mg) also gave lactones 12 in similar yields.
4.7.1. 2,3-O-Isopropylidene-4-C-methyl-5-O-trityl-D-ribono-1,4-lactone (12a)
Treatment of 11a (51 mg, 0.11 mmol) with NMO/TPAP, using the procedure reported
in Section 4.7, gave 12a (40 mg, 80%): 1H NMR δ 1.30 (s, 3H, CH3), 1.35 (s, 3H, CH3),
1.40 (s, 3H, CH3), 2.91 (d, J = 10.2 Hz, 1H, H5), 3.50 (d, J = 10.2 Hz, H1, H5’), 4.20 (d,
J = 5.6 Hz, 1H, H2), 5.01 (d, J = 5.6 Hz, 1H, H3), 7.25–7.38 (m, 15H, Ar); 13C NMR δ
16.40 (C1a) 25.90 and 26.78 (CMe2), 66.65 (CPh3), 67.63 (C5), 77.70 (C2), 79.77 (C3),
88.56 (C4), 126.07 (CMe2), 127.46 and 128.25 and 128.67 and 146.87 (Ar), 172.07 (C1);
HRMS calcd for C28H28O5Na+ [M+Na]+ 467.1829, found 467.1847.
4.7.2. 2,3-O-Isopropylidene-4-C-hexyl-5-O-trityl-D-ribono-1,4-lactone (12b)
Treatment of 11b (37 mg, 0.09 mmol) with NMO/TPAP, using the procedure reported in
Section 4.7, gave 12b (35 mg, 94%): 1H NMR δ 0.80 (t, J = 6.6 Hz, 3H, H6a), 1.19–1.21
(m, 8H, H2a–H5a), 1.24 (s, 3H, CH3), 1.40 (s, 3H, CH3), 1.50–1.60 (m, 2H, H1a), 2.85 (d,
J = 10.2 Hz, 1H, H5), 3.51 (d, J = 10.2 Hz, 1H, H5’), 4.10 (d, J = 5.6 Hz, 1H, H2), 5.01 (d,
J = 5.6 Hz, 1H, H3), 7.25–7.38 (m, 15H, Ar); 13C NMR δ 13.98 (C6a), 22.45, 23.33, 29.42,
31.30 (C2a–C5a), 25.91 and 26.76 (CMe2), 31.60 (C1a), 66.29 (C5), 77.57 (C3), 80.11 (C2),
87.75 (C4), 88.26 (CPh3), 112.92 (CMe2), 127.41, 128.16, 128.52 and 142.95 (Ar), 174.41
(C1); MS (ESI+) m/z 532 (M+NH4)+.
4.7.3. 2,3-O-Isopropylidene-4-C-octyl-5-O-trityl-D-ribono-1,4-lactone (12c)
Treatment of 11c (48 mg, 0.08 mmol) with NMO/TPAP, using the procedure reported in
Section 4.7, gave 12c (32 mg, 95%): 1H NMR δ 0.80–0.84 (m, 3H, H8a), 1.10–1.20 (s, 12H,
H2a–H7a), 1.25 (s, CH3), 1.40 (s, CH3), 1.50–1.60 (m, 2H, H1a), 2.90 (d, J = 10.1 Hz, 1H,
H5), 3.55 (d, J = 10.2 Hz, 1H, H5’), 4.10 (d, J = 5.6 Hz, 1H, H2), 5.01 (d, J = 5.6 Hz, 1H,
H3), 7.25–7.38 (m, 15H, Ar); 13C NMR δ 14.23 (C8a), 22.77, 23.50, 29.24, 29.29, 30.06,
31.72 (C2a–C7a), 26.06 and 26.92 (CMe2), 31.93 (C1a), 66.39 (C5), 77.57 (C3), 80.11 (C2),
87.94 (C4), 88.38 (CPh3), 113.07 (CMe2), 127.56, 128.31, 128.65, 143.07 (Ar), 174.63 (C1);
MS (ESI+) m/z 560 (M+NH4)+.
Note: When oxidation of 11c was carried out overnight instead of 6 h, a second minor
product ( ∼30%) was formed in addition to 12c. The minor product had the following
1
ribosyl peaks: H NMR δ 3.75 (d, J = 11.6 Hz, 1H), 3.91 (d, J = 11.6 Hz, 1H), 4.60 (d,
J = 5.6 Hz, 1H), 4.90 (d, J = 5.6 Hz, 1H).
4.7.4. 2,3-O-Isopropylidene-5-O-trityl-4-C-vinyl-D-ribono-1,4-lactone (12d)
Treatment of 11d (100 mg, 0.21 mmol) with NMO/TPAP, using the procedure reported in
Section 4.7, gave 12d (90 mg, 95%): 1H NMR δ 1.22 (s, 3H, CH3), 1.26 (s, 3H, CH3), 2.91

318
C. CHBIB ET AL.
(d, J = 10.2 Hz, 1H, H5), 3.50 (d, J = 10.3 Hz, H1, H5’), 4.20 (d, J = 5.6 Hz, 1H, H2),
=
5.00 (d, J = 5.6 Hz, 1H, H3), 5.21 (d, J = 11.2 Hz, 1H, CH CHH), 5.34 (d, J = 17.4 Hz,
1H, CHH ), 5.61 (dd, J = 11.2, 17.4 Hz, 1H, CH CHH), 7.25–7.38 (m, 15 H); 13C
=
NMR δ 25.92 and 26.64 (CMe2), 53.50 (CPh3), 65.50 (C5), 80.01 (C2), 82.03 (C3), 88.87
=
(C4), 112.03 (CH CH2), 118.50 (CMe2), 127.29, 127.95, 129.69 and 145.01 (+Ar), 146.85
+
=
(CH CH2), 174.14 (C1); HRMS (TOF) m/z calcd for C29H28O5Na [M+Na] 479.1829;
found 479.1829.
4.7.5. 2,3-O-Isopropylidene-4-C-4-methoxyphenyl-5-O-trityl-D-ribono-1,4-lactone
(12e)
Treatment of 11e (90 mg, 0.16 mmol) with NMO/TPAP, using the procedure reported in
Section 4.7, gave 12e (73 mg, 82%): 1H NMR δ 1.22 (s, 3H, CH3), 1.25 (s, 3H, CH3), 3.25
(d, J = 10.5 Hz, 1H, H5’), 3.35 (d, J = 10.5 Hz, 1H, H5), 3.80 (s, 3H, CH3O), 4.48 (d,
J = 5.5 Hz, 1H, H2), 5.20 (d, J = 5.5 Hz, 1H, H3), 6.82 (d, J = 8.8 Hz, 2H, Ar), 7.12 (d,
J = 9.7 Hz, 2H, Ar), 7.25–7.38 (m, 15H, Ar); 13C NMR δ 25.92 and 26.64 (CMe2), 55.18
(CH3O), 62.94 (CPh3), 68.79 (C5), 77.71 (C2), 80.77 (C3), 88.87 (C4), 113.60 (CMe2),
126.9, 127.25, 128.75 and 159.10, (Ar), 128.57, 129.68, 132.91 and 146.40 (Ar), 174.14 (C1);
MS (ESI) m/z 554 (M+NH4)+.
4.8. General procedure for detritylation of 4-C-substituted ribono-1,4-lactones
TFA (0.5 mL) and CH2Cl2 (5 mL) were added to a stirred solution of 12 (0.1 mmol) at
ambient temperature for 6 h. The volatiles were evaporated and the residue co-evaporated
with toluene. The oily residue was partitioned between aqueous NaHCO3 and CH2Cl2.
The separated organic layer was washed with brine, dried (MgSO4), evaporated and was
purified on a silica gel column (hexane/EtOAc, 8:2).
4.8.1. 2,3-O-Isopropylidene-4-C-methyl-D-ribono-1,4-lactone (13a)
Treatment of 12a (44 mg, 0.1 mmol) with TFA, using the procedure reported in Section
4.8, gave 13a (13 mg, 66%): 1H NMR δ 1.32 (s, 3H, CH3), 1.35 (s, 3H, CH3), 1.42 (s, 3H,
CH3), 3.60 (d, J = 11.6 Hz, 1H, H5), 3.71 (d, J = 11.6 Hz, H1, H5’), 4.55 (d, J = 5.6 Hz,
1H, H2), 4.90 (d, J = 5.6 Hz, 1H, H3); 13C NMR δ 16.42 (C1a), 25.81 and 26.76 (CMe2),
67.61 (C5), 77.82 (C2), 80.01 (C3), 86.35 (C4), 113.02 (CMe2), 174.46 (C1); HRMS (TOF)
m/z calcd for C9H14O5Na+ [M+Na]+ 225.0733; found 225.0734.
4.8.2. 2,3-O-Isopropylidene-4-C-hexyl-D-ribono-1,4-lactone (13b)
Treatment of 12b (31 mg, 0.06 mmol) with TFA, using the procedure reported in Section
1
4.8 (flash column chromatography; 80% hexane/EtOAc), gave 13b (12.5 mg, 80%): H
NMR δ 0.80 (t, J = 6.6 Hz, 3H, H6a), 1.19–1.21 (m, 8H, H2a–H5a), 1.41 (s, 3H, CH3), 1.50
(s, 3H, CH3), 1.50–1.60 (m, 2H, H1a), 3.75 (d, J = 11.8 Hz, 1H, H5), 3.85 (d, J = 11.4 Hz,
1H, H5’), 4.65 (d, J = 5.6 Hz, 1H, H2), 4.96 (d, J = 5.6 Hz, 1H, H3); 13C NMR δ 14.06
(C6a), 22.47, 23.54, 29.42, 31.48 (C2a–C5a), 25.79 and 26.78 (CMe2), 31.91 (C1a), 65.83
(C5), 77.20 (C3), 80.63 (C2), 89.73 (C4), 112.85 (CMe2), 172.67 (C1); HRMS (TOF) m/z
calcd for C14H24O5Na+ [M+Na]+ 295.1516, found 295.1516.

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4.8.3. 2,3-O-Isopropylidene-4-C-octyl-D-ribono-1,4-lactone (13c)
Treatment of 12c (35 mg, 0.065 mmol) with TFA, using the procedure reported in Section
1
4.8, gave 13c (16 mg, 75%): H NMR δ 0.80 (t, J = 6.6 Hz, 3H, H8a), 1.30–1.32 (m,
12H, H2a–H7a), 1.40 (s, 3H, CH3), 1.50 (s, 3H, CH3), 1.50–1.60 (m, 2H, H1a), 3.75 (d,
J = 11.6 Hz, 1H, H5), 3.85 (d, J = 11.6 Hz, 1H, H5’), 4.65 (d, J = 5.6 Hz, 1H, H2), 4.95 (d,
J = 5.6 Hz, 1H, H3);13C NMR δ 14.25 (CH3, C8a), 22.74, 23.64, 29.30, 29.41, 30.21, 31.27
(C2a–C7a), 25.93 and 26.9 (CMe2), 31.98 (C1a), 65.92 (C5), 77.46 (C3), 79.91 (C2), 88.94
(C4), 113.0 (CMe2), 174.98 (C1); HRMS (TOF) m/z calcd for C16H28O5Na+ [M+Na]+
323.1829; found 323.1915.
4.8.4. 2,3-O-Isopropylidene-4-C-vinyl-D-ribono-1,4-lactone (13d)
Treatment of 12d (30 mg, 0.065 mmol) with TFA, using the procedure reported in Section
4.8 (flash column chromatography; 80% hexane/EtOAc), gave somehow an unstable prod-
uct 13d (5 mg, 35%): 1H NMR δ 1.22 (s, 3H, CH3), 1.26 (s, 3H, CH3), 3.61 (d, J = 11.7 Hz,
1H, H5), 3.65 (d, J = 11.8 Hz, 1H, H5’), 4.60 (d, J = 5.6 Hz, 1H, H2), 4.82 (d, J = 5.6 Hz,
=
=
1H, H3), 5.24 (d, J = 11.3 Hz, 1H, CH CHH), 5.34 (d, J = 17.5 Hz, 1H, C CHH), 5.71
(dd, J = 11.2, 17.5 Hz, 1H, CH CHH); 13C NMR δ 25.87, 26.70 (CMe2), 66.37 (C5),
=
=
=
76.70 (C2), 80.01 (C3), 87.95 (C4), 113.29 (CMe2), 118.21 (CH CH2), 130.53 (CH CH2),
174.06 (C1); HRMS (TOF) m/z calcd for C10H14O5Na+ [M+Na]+ 237.0733; found
237.0733.
4.8.5. 2,3-O-Isopropylidene-4-C-4-methoxyphenyl-D-ribono-1,4-lactone (13e)
Treatment of 12e (70 mg, 0.13 mmol) with TFA, using the procedure reported in Section
4.8 (flash column chromatography; 80% hexane/EtOAc), gave 13e (23 mg, 70%): 1H NMR
δ 1.22 (s, 3H, CH3), 1.25 (s, 3H, CH3), 3.80 (s, 3H, CH3O), 3.85 (d, J = 12.3 Hz, 1H,
H5), 3.95 (d, J = 12.5 Hz, 1H, H5’), 4.95 (d, J = 5.4 Hz, 1H, H2), 5.15 (d, J = 5.3 Hz,
1H, H3), 6.82 (d, J = 8.8 Hz, 2H, Ar), 7.12 (d, J = 9.0 Hz, 2H, Ar); 13C NMR δ 25.83
and 26.65 (CMe2), 55.25 (CH3O), 68.50 (C5), 77.41 (C2), 80.57 (C3), 90.12 (C4), 112.93
(CMe2), 113.76, 126.17, 126.89, 159.33 (Ar); 174.86 (C1); HRMS (TOF) m/z calcd for
C15H18O6Na+ [M+Na]+ 317.0996; found 317.0982.
4.9. 2,3-O-Isopropylidene-4-C-hexyl-5-O-trityl-D-ribofuranose (14b)
LiEt3BH (1M/THF, 0.18 mL, 0.18 mmol) was added dropwise to a solution of 12b (36 mg,
0.07 mmol) in CH2Cl2 (0.5 mL) and the resulting mixture was stirred for 30 min at −20°C
under N2 atmosphere. The reaction was quenched with MeOH and the volatiles were evap-
orated. The residue was partitioned between CH2Cl2 and NaHCO3, washed with brine
and dried with anhydrous MgSO4. The resulting oil was column chromatographed (75:15,
hexane/EtOAc) to give 14b (α/β; 1:3; 20 mg, 54%). The major β-anomer had: 1H NMR δ
0.80 (t, J = 6.6 Hz, 3H, H6a), 1.20–1.28 (m, 8H, H2a–H5a), 1.33 (s, 3H, CH3), 1.41 (s, 3H,
CH3), 1.50–1.60 (m, 2H, H1a), 3.16 (d, J = 10.1 Hz, 1H, H5), 3.32 (d, J = 10.1 Hz, 1H,
H5’), 3.74 (d, J = 8.8 Hz, OH), 4.50 (d, J = 6.0 Hz, 1H, H3), 4.75 (d, J = 6.0 Hz, 1H, H2),
5.15 (d, J = 8.4 Hz, 1H, H1). 7.25–7.38 (m, 15H, Ar). The minor α-anomer had: 1H NMR δ
0.80 (t, J = 6.6 Hz, 3H, H6a), 1.20–1.28 (m, 8H, H2a–H5a), 1.33 (s, 3H, CH3), 1.41 (s, 3H,
CH3), 1.50–1.60 (m, 2H, H1a), 2.94 (d, J = 9.9 Hz, 1H, H5), 3.25 (d, J = 9.9 Hz, 1H, H5’),
3.86 (d, J = 11.5 Hz, OH), 4.20 (d, J = 6.1 Hz, 1H, H3), 4.62 (dd, J = 4.2, 6.1 Hz, 1H, H2),

320
C. CHBIB ET AL.
5.61 (dd, J = 4.2, 11.5 Hz, 1H, H1), 7.25–7.38 (m, 15H, Ar). 13C NMR for the mixture of
α/β-anomers: δ 14.01 (C6a), 23.61 and 23.94 (CMe2), 24.57 and 24.98 (CMe2), 25.99, 26.22,
29.65, 31.51 (C2a–C5a), 31.83 (C1a), 67.33 and 68.18 (C5), 80.01 and 82.78 (C2), 83.09 and
83.82 (C3), 88.05 and 88.12 (C4), 96.55 and 102.85 (C1), 112.06 and 112.32 (CMe2), 127.22,
127.45, 127.97, 128.05, 128.65, 128.76, 142.90, 143.49 (Ar); HRMS (TOF-ESI) m/z calcd for
C33H40O5Na+ [M+Na]+ 539.2768; found 539.2789.
4.10. General procedure for the synthesis of 5-O-mesyl-4-C-substituted
ribono-1,4-lactones 15
TEA (48 μL, 34 mg, 0.33 mmol) and MsCl (11.4 μL, 19.5 mg, 0.15 mmol) were added to a
stirred solution of 13 (0.1 mmol) in dry CH2Cl2 (2 mL) at 0°C (ice bath) under N2 atmo-
sphere. After 1 h, the reaction mixture was partitioned between CH2Cl2 and diluted HCl.
The separated organic layer was washed with aqueous solution of NaHCO3, brine and dried
over anhydrous MgSO4. Volatiles were evaporated and the residue was purified on silica
column chromatography (hexane/EtOAc, 6:4).
4.10.1. 2,3-O-Isopropylidene-4-C-hexyl-5-O-mesyl-D-ribono-1,4-lactone (15b)
Treatment of 13b (27 mg, 0.1 mmol) with MsCl, using the procedure reported in Section
4.10, gave 15b (21 mg, 60%): 1H NMR δ 0.80 (t, J = 6.6 Hz, 3H, H6a), 1.20–1.28 (m, 8H,
H2a–H5a), 1.33 (s, 3H, CH3), 1.41 (s, 3H, CH3), 1.50–1.60 (m, 2H, H1a), 2.99 (s, 3H,
Ms), 4.20 (d, J = 11.0 Hz, 1H, H5), 4.32 (d, J = 11.0 Hz, 1H, H5’), 4.60 (d, J = 5.7 Hz,
1H, H2), 4.88 (d, J = 5.7 Hz, 1H, H3); 13C NMR δ 14.03 (CH3, C6a), 22.46, 23.36, 29.55,
31.38 (C2a–C5a), 25.78 and 26.69 (CMe2), 31.45 (C1a), 37.62 (Ms), 71.80 (C5), 76.70
(C3), 78.91 (C2), 85.77 (C4), 113.79 (CMe2), 173.21 (C1); HRMS (TOF-ESI) m/z calcd
for C15H26O7SNa+ [M+Na]+ 373.1291; found 373.1307.
4.10.2. 2,3-O-Isopropylidene-5-O-mesyl-4-C-octyl-D-ribono-1,4-lactone (15c)
Treatment of 13c (32 mg, 0.1 mmol) with MsCl, using the procedure reported in Section
4.10, gave 15c (19 mg, 68%): 1H NMR δ 0.80 (t, J = 6.6 Hz, 3H, H8a), 1.20–1.28 (m, 12H,
H2a–H7a), 1.35 (s, 3H, CH3), 1.41 (s, 3H, CH3), 1.50–1.60 (m, 2H, H1a), 3.05 (s, 3H,
Ms), 4.20 (d, J = 10.9 Hz, 1H, H5), 4.32 (d, J = 10.9 Hz, 1H, H5’), 4.60 (d, J = 5.6 Hz,
1H, H2), 4.84 (d, J = 5.6 Hz, 1H, H3); 13C NMR δ 14.24 (CH3, C8a), 22.78, 23.52, 29.22,
29.30, 30.02, 31.58 (C2a–C7a), 25.92 and 26.82 (CMe2), 31.94 (C1a), 37.76 (Ms), 71.93
(C5), 76.88 (C3), 79.05 (C2), 85.91 (C4), 113.92 (CMe2), 173.34 (C1); MS (ESI) m/z 401
(M+Na)+.
4.10.3. 2,3-O-Isopropylidene-5-O-mesyl-4-C-4-methoxyphenyl-D-ribono-1,4-lactone
(15e)
Treatment of 13e (24 mg, 0.08 mmol) with MsCl, using the procedure reported in Section
4.10, gave 15e (25 mg, 83%): 1H NMR δ 1.35 (s, 3H, CH3), 1.41 (s, 3H, CH3), 3.0 (s, 3H,
Ms), 3.80 (s, 3H, CH3O), 4.20 (d, J = 11.2 Hz, 1H, H5), 4.55 (d, J = 11.2 Hz, 1H, H5’), 5.01
(d, J = 5.5 Hz, 1H, H2), 5.15 (d, J = 5.5 Hz, 1H, H3), 6.82 (d, J = 8.8 Hz, 2H, Ar), 7.12 (d,
J = 9.0 Hz, 2H, Ar); 13C NMR δ 25.90 and 26.58 (CMe2), 44.10 (Ms), 55.33 (CH3O), 73.26
(C5), 77.35 (C2), 79.71 (C3), 87.04 (C4), 113.79 (CMe2), 114.10, 124.91, 127.00, 159.95

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(Ar); 173.01 (C1); HRMS (TOF-ESI) m/z calcd for C16H20O8SNa+ [M+Na]+ 395.0771;
found 395.0793.
4.11. General procedure for the synthesis of 4-C-substituted S-ribosylhomocyteine
lactones 16
Step a. H2O (0.24 mL) and tris(2-carboxyethyl)phosphine hydrochloride (88 mg,
0.31 mmol) were added to a stirred solution of N,N’-di(tert-butoxycarbonyl)-l-homocys-
tine di(tert-butyl) ester[13] (160 mg, 0.28 mmol) in anhydrous DMF (2.4 mL) at ambi-
ent temperature under Ar atmosphere. After 20 h, the reaction mixture was partitioned
between EtOAc, and saturated NaHCO3/H2O. The aqueous layer was extracted with
EtOAc, and the combined organic layer was washed with brine, dried (Na2SO4), and con-
centrated to give N-tert-butoxycarbonyl-l-homocysteine tert-butyl ester (159 mg, 99%) as
a colorless oil of sufficient purity to be directly used in the next step.
Step b. LDA (2M/THF and heptanes, 48 μl, 0.96 mmol) was added slowly to a stirred
solution of the freshly prepared protected l-homocysteine (29 mg, 0.1 mmol; from step (a)
in anhydrous DMF 1.5 ml under Ar atmosphere at 0°C (ice bath). After 30 min, a solu-
tion of 15 (0.035 mmol) in DMF (1 mL) was added by a syringe and the mixture was left
stirring for 15 min at 0°C then at room temperature for 24 h. The reaction was quenched
with NH4Cl and the volatiles were evaporated under high vacuum. The residue was par-
titioned between EtOAc and NaHCO3, washed with brine and dried over anhydrous
MgSO4. Volatiles were evaporated and the resulting oil was column chromatographed
(hexane/EtOAc, 8:2).
4.11.1. S-(2,3-O-Isopropylidene-4-C-hexyl-D-ribono-1,4-lactone-5-yl)-N-tert-
butoxycarbonyl-l-homocysteine tert-butyl ester (16b)
Treatment of 15b (11 mg, 0.031 mmol) with homocysteinate salt, using the procedure
reported in Section 4.11, gave 16b (18 mg, 65%): 1H NMR δ 0.80 (t, J = 6.6 Hz, 3H, H6a),
1.20–1.28 (m, 8H, H2a–H5a), 1.31 (s, 3H, CH3), 1.39 and 1.41 (2 × s, 2 × 9H, 2 × t-Bu),
1.42 (s, 3H, CH3), 1.50–1.60 (m, 2H, H1a), 1.75–1.85 (m, 1H, H8), 1.95–2.05 (m, 1H, H8’),
2.46–2.54 (m, 2H, H7,7’), 2.72 (d, J = 14.7 Hz, 1H, H5), 2.80 (d, J = 14.7 Hz, 1H, H5’),
4.20–4.25 (m, 1H, H9), 4.40 (d, J = 5.9 Hz, 1H, H3), 5.00 (br. d, J = 7.8 Hz, 1H, NH), 5.10
( d, J = 5.9 Hz, 1H, H2); 13C NMR δ 14.01 (C6a), 22.5 and 22.7 (CMe2), 23.45, 25.66, 26.56,
30.67 (C2a–C5a), 27.9 (C7), 28.08 (t-Bu), 28.32 (t-Bu), 34.34 (C1a), 35.8 (C8), 39.86 (C5),
53.6 (C9), 77.0 (C2), 77.20 (C3), 80.59 (t-Bu), 82.41 (t-Bu), 88.98 (C4), 113.30 (CMe2),
156.1 (Boc), 171.3 and 174.0 (C1 and C10); HRMS (TOF-ESI) calcd for C27H48NO8S+
[M+H]+ 546.3095; found 546.3104.
4.11.2. S-(2,3-O-Isopropylidene-4-C-4-methoxyphenyl-D-ribono-1,4-lactone-5-yl)-N-
tert-butoxycarbonyl-l-homocysteine tert-butyl ester (16e)
Treatment of 15e (22 mg, 0.07 mmol) with homocysteinate salt, using the procedure
reported in Section 4.11, gave 16e (20 mg, 48%): 1H NMR δ 1.35 (s, 3H, CH3), 1.41 (s, 3H,
CH3), 1.39 and1.41 (2 × s, 2 × 9H, 2 × t-Bu), 1.75–1.89 (m, 1H, H8), 1.95–2.05 (m, 1H,
H8’), 2.52–2.68 (m, 2H, H7,7’), 2.85 (d, J = 14.8 Hz, 1H, H5), 3.20 (d, J = 15.0 Hz, 1H,
H5’), 3.80 (s, 3H, OCH3), 4.20–4.25 (m, 1H, H9), 4.80 (d, J = 5.8 Hz, 1H, H3), 5.01 (br. d,
J = 8.1 Hz, 1H, NH), 5.30 (d, J = 5.8 Hz, 1H, H2), 6.82 (d, J = 8.8 Hz, 2H, Ar), 7.12 (d,

322
C. CHBIB ET AL.
J = 9.0 Hz, 2H, Ar); 13C NMR δ 25.9 and 26.5 (CMe2), 28.1 (t-Bu), 28.4 (t-Bu), 28.9 (C7),
31.0 (C8), 43.9 (C5), 53.1 (C9), 55.4 (OCH3), 77.16 (C2), 77.37 (C3), 81.6 (t-Bu), 82.6 (t-
Bu), 90.2 (C4), 113.5 (CMe2), 113.7, 126.7, 130.1, 156.2 (Ar), 155.8 (Boc), 171.2 and 172.0
(C1 and C10); HRMS (TOF-ESI) calcd for C28H41NO9SNa+ [M+Na]+ 590.2394; found
590.2378.
4.12. General procedure for deprotection of 4-C-substituted S-ribosylhomocyteine
lactones
Compound 16 (0.03 mmol) was stirred in TFA (2 mL) at 0°C for 1 h and then at ambi-
ent temperature for 3 h. H2O (0.1 mL) was then added and stirring was continued for
an additional 1 h. Volatiles were evaporated in vacuum below 30°C and the residue was
coevaporated with MeCN (2 × 0.5 mL). The crude product was redissolved in deionized
water (2.5 mL) and washed with CHCl3 (2 × 1 mL). The aqueous layer was evaporated in
vacuum below 30°C.
4.12.1. S-(4-C-Hexyl-D-ribono-1,4-lactone-5-yl)-l-homocysteine (17b)
Treatment of 16b (17 mg, 0.03 mmol) with TFA, using the procedure reported in
Section 4.12, gave 17b (7 mg, 60%). This product was additionally purified by HPLC
(CH3CN/H2O, 15:85; tR = 21.0 min) to give 6.5 mg (55%) of 17b 1H NMR (D2O) δ 0.82
(t, J = 6.6 Hz, 3H, H6a), 1.20–1.28 (m, 8H, H2a–H5a), 1.45–1.50 (m, 2H, H1a), 1.87–2.00
(m, 1H, H8), 2.05–2.12 (m, 1H, H8’), 2.45–2.55 (m, 2H, H7,7’), 2.82 (d, J = 13.6 Hz, 1H,
H5), 2.87 (d, J = 13.6 Hz, 1H, H5’), 4.20 (d, J = 5.4 Hz, 1H, H3), 4.21–4.23 (m, 1H, H9),
4.72 (d, J = 5.4 Hz, 1H, H2); 13C NMR (D2O) δ 15.01 (C6a), 23.20, 23.56, 23.90, 29.20
(C2a–C5a), 27.3 (C7), 29.73 (C8), 32.10 (C1a), 41.99 (C5), 52.4 (C9), 72.55 (C2), 78.50
(C3), 88.50 (C4), 172.3 and 173.5 (C1 and C10); HRMS calcd for C15H27NO6S+ [M+Na]+
372.1451; found 372.1469.
4.12.2. S-(4-C-Octyl-D-ribono-1,4-lactone-5-yl)-l-homocysteine (17c)
Step a. Treatment of 15c (24 mg, 0.063 mmol) with homocysteinate lithium salt, using the
procedure reported in Section 4.11, gave 16c contaminated with protected homocysteine
(∼1:1, 40 mg). Compound 16c had: 1H NMR δ 0.80 (t, J = 6.6 Hz, 3H, H8a), 1.20–1.25
(m, 12H, H2a–H7a), 1.26 (s, 3H, CH3), 1.40 (s, 3H, CH3), 1.39 and 1.41 (2 × s, 2 × 9H,
2 × t-Bu), 1.50–1.60 (m, 2H, H1a), 1.75–1.89 (m, 1H, H8), 1.9–2.0 (m, 1H, H8’), 2.48–2.54
(m, 2H, H7,7’), 2.80–2.83 (m, 2H, H5,5’), 4.20–4.26 (m, 1H, H9), 4.40 (d, J = 5.9 Hz, 1H,
H3), 5.05 (br. d, J = 7.6 Hz, 1H, NH), 5.15 (d, J = 5.9 Hz, 1H, H2). Step b. Treatment of
the crude 16c (∼1:1, 40 mg; Step a) with TFA (2 mL), using the procedure reported in
Section 4.12, gave an oily residue that was partitioned between water and CHCl3. The
aqueous layer was evaporated in vacuum below 30°C and the residue (20 mg) was divided
into two portions. Each portion of crude 17c was dissolved in deionized water/MeCN
(2.5 mL, 19:1, v/v) and was injected into the Sep-Pak cartridge (C18 classic column). The
columns were eluted with deionized water (5 mL), a second portion of deionized water
(5 mL) and ethanol (5 mL). The combined water eluents contained mainly Hcy (TLC and
1H NMR), while the combined ethanol eluents were evaporated in vacuum to give 17c
(5 mg, 21% from 15c): 1H NMR (MeOH-d4) δ 0.82 (t, J = 6.6 Hz, 3H, H8a), 1.20–1.28 (m,
12H, H2a–H7a), 1.50–1.60 (m, 2H, H1a), 1.90–2.00 (m, 1H, H8), 2.05–2.12 (m, 1H, H8’),

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2.55–2.65 (m, 2H, H7,7’), 2.80 (d, J = 13.8 Hz, 1H, H5), 2.87 (d, J = 13.9 Hz, 1H, H5’),
4.20 (d, J = 5.4 Hz, 1H, H3), 4.19–4.21 (m, 1H, H9), 4.75 (d, J = 5.4 Hz, 1H, H2); 13C
NMR (MeOH-d4) δ 15.01 (C8a), 23.00, 23.50, 23.85, 29.00, 30.67, 30.51 (C2a–C7a), 27.40
(C7), 29.7 (C8), 32.07 (C1a), 39.86 (C5), 52.21 (C9), 71.54 (C2), 77.20 (C3), 84.59 (C4),
172.21 and 173.52 (C1 and C10); HRMS calcd for C17H31NNaO6S+ [M+Na]+ 400.1764;
found 400.1783.
Note. By varying the reaction conditions different quantities of 2,3-O-isopropylidene-
4-C-octyl-d-ribono-1,5-lactone were isolated during the column chromatography of the
crude reaction mixture from step a: 1H NMR δ 0.88 (t, J = 6.6 Hz, 3H, H8a), 1.25–1.32
(m, 12H, H2a–H7a), 1.40 (s, 3H, CH3), 1.50 (s, 3H, CH3), 1.62–1.70 (m, 2H, H1a), 3.86 (m,
2H, H5,5’), 4.60 (d, J = 5.7 Hz, 1H, H2), 4.85 (d, J = 5.7 Hz, 1H, H3);13C NMR δ 14.23
(CH3, C8a), 22.76, 22.87, 29.29, 29.48, 29.91, 31.92 (C2a–C7a), 25.93 and 26.9 (CMe2),
35.47 (C1a), 63.45 (C5), 76.55 (C3), 80.07 (C2), 87.05 (C4), 114.57 (CMe2), 173.25 (C1);
HRMS (TOF) m/z calcd for C16H28O5Na+ [M+Na]+ 323.1798; found 323.1805.
4.12.3. S-(4-C-4-Methoxyphenyl-D-ribono-1,4-lactone-5-yl)-l-homocysteine (17e)
Treatment of 16e (11.4 mg, 0.02 mmol) with TFA (1 mL), using the procedure reported
in Section 4.12, gave 17e (5.6 mg, 75%): 1H NMR (MeOH-d4) δ 1.80–1.83 (m, 1H, H8),
1.90–1.92 (m, 1H, H8’), 2.50–2.65 (m, 2H, H7,7’), 2.85 (d, J = 14.8 Hz, 1H, H5), 3.20 (d,
J = 15.1 Hz, 1H, H5’), 3.80 (s, 3H, CH3O), 4.22–4.27 (m, 1H, H9), 4.60 (d, J = 5.8 Hz,
1H, H3), 4.90 (d, J = 5.8 Hz, 1H, H2), 6.82 (d, J = 8.8 Hz, 2H, Ar), 7.12 (d, J = 9.0 Hz,
2H, Ar); 13C NMR (MeOH-d4) δ 27.33 (C7), 29.73 (C8), 41.37 (C5), 52.50 (C9), 55.33
(CH3O), 74.40 (C2), 78.20 (C3), 85.40 (C4), 117.20, 125.81, 127.00, 162.28 (Ar), 172.31,
173.49 (C1 and C10); HRMS calcd for C16H21NO7SNa+ [M+Na]+ 394.0931; found
394.0908.
4.13. General procedure for the reduction of lactones. Synthesis of 4-C-substituted
S-ribosylhomocyteines 19
LiEt3BH (1M/THF, 0.045 mL, 0.045 mmol) was added dropwise to a solution of 0.02 mmol
of 16 in CH2Cl2 (1 mL) or 17 in THF/CH2Cl2 (1:1; 1 mL) and the resulting mixture was
stirred at −20°C for 30 min under N2 atmosphere. MeOH (0.5 mL) was then slowly added
to quench the reaction and volatiles were evaporated in vacuum below 25°C. The residue
for the protected products 18 was partitioned between CH2Cl2/NaHCO3, washed with
brine, dried (MgSO4) and was column chromatographed (75:25, hexane/EtOAc); whereas
the residue for the deprotected product 19 was redissolved in deionized H2O/MeOH (4:1,
2.5 mL) and washed with CHCl3 (2 × 1 mL) and then the aqueous layer was evaporated
in vacuum below 30°C. The 4-C-substituted SRH analogues 19 are somehow unstable and
need to be manipulated with care but are stable when stored as powder or well-dried syrup
in a refrigerator at 4°C for a month.
4.13.1. S-(5-Deoxy-4-C-hexyl-D-ribofuranos-5-yl)-l-homocysteine (19b)
Step a. Treatment of 16b (10.9 mg, 0.02 mmol) with LiEt3BH, using the procedure reported
in Section 4.13, gave 2,3-O-isopropylidene-5-[(tert-butoxycarbonyl)-l-homocysteine tert-
butyl ester]-4-C-hexyl-D-ribofuranose 18b (α/β, ∼1:9, 9.5 mg, 90%). The major β
anomer had:1H NMR δ 0.80 (t, J = 6.6 Hz, 3H, H6a), 1.20–1.28 (m, 8H, H2a–H5a),

324
C. CHBIB ET AL.
1.35 and 1.41 (2 × s, 2 × 9H, 2 × t-Bu), 1.35 (s, 6H, 2 × CH3), 1.50–1.60 (m, 2H,
H1a), 1.91–2.02 (m, 2H, H8,8’), 2.48–2.58 (m, 2H, H7,7’), 2.60 (d, J = 12.8 Hz, 1H,
H5), 2.94 (d, J = 12.6 Hz, 1H, H5’), 4.19–4.21 (m, 1H, H9), 4.30 (d, J = 5.9 Hz, 1H,
H3), 4.92 (d, J = 5.9 Hz, 1H, H2), 5.19–5.21 (m, 1H, NH), 5.35 (s, 1H, H1). The
minor α anomer had a peak for H1 at δ 5.47 (d, J = 3.9 Hz). Step b. Treatment
of 18b (α/β, ∼1:9; 9.5 mg, 0.02 mmol) with in TFA (1 mL), using the procedure
reported in Section 4.12, gave 19b (α/β, ∼1:9; 4 mg, 75%). The major β anomer
1
had: H NMR (D2O) δ 0.80 (t, J = 6.6 Hz, 3H, H6a), 1.20–1.28 (m, 8H, H2a–H5a),
1.50–1.60 (m, 2H, H1a), 1.91–2.01 (m, 2H, H8,8’), 2.48–2.58 (m, 2H, H7,7’), 2.63
(d, J = 12.8 Hz, 1H, H5), 2.94 (d, J = 12.6 Hz, 1H, H5’), 4.12 (t, J = 5.9 Hz, 1H,
H2), 4.19–4.21 (m, 1H, H9), 4.20 (d, J = 5.9 Hz, 1H, H3), 5.33 (s, 1H, H1); MS
(ESI−) m/z 350 (MH−). HRMS calcd for C15H29NO6SNa+ [M+Na]+ 374.1608, found
374.1617.
4.13.2. S-(5-Deoxy-4-C-octyl-D-ribofuranos-5-yl)-l-homocysteine (19c)
Treatment of 17c (6 mg, 0.01 mmol) with LiEt3BH (0.03 mL), using the procedure reported
1
in Section 4.13, gave 19c (α/β, ∼1:3; 4 mg, 60%). The major β anomer had: H NMR
(MeOH-d4) δ 0.80 (t, J = 6.6 Hz, 3H, H8a), 1.21–1.32 (m, 12H, H2a–H7a), 1.50–1.60 (m,
2H, H1a), 1.9–2.0 (m, 2H, H8,8’), 2.48–2.58 (m, 2H, H7,7’), 2.79 (d, J = 12.8 Hz, 1H, H5),
2.90 (d, J = 12.6 Hz, 1H, H5’), 4.15 (t, J = 5.9 Hz, 1H, H2), 4.19–4.21 (m, 1H, H9), 4.20
(d, J = 5.9 Hz, 1H, H3), 5.19–5.21 (m, 1H, NH), 5.39 (s, 1H, H1), [the minor α anomer
had a peak for H1 at δ 5.44 (d, J = 3.5 Hz)]; 13C NMR (MeOH-d4) δ 15.01 (C8a), 23.00,
23.50, 23.85, 29.00, 30.67, 30.51 (C2a–C7a), 27.3 (C7), 29.6 (C8), 32.07 (C1a), 41.99 (C5),
50.51 (C9), 69.77 (C3), 72.09 (C2), 87.16 (C4), 99.90 (C1), 172.62 (C10); HRMS calcd for
C17H33NO6SNa+ [M+Na]+ 402.1921, found 402.1933.
4.13.3. S-(5-Deoxy-4-C-4-methoxyphenyl-D-ribofuranos-5-yl)-l-homocysteine (19e)
Step a. Treatment of 16e (11.3 mg, 0.02 mmol) with LiEt3BH, using the procedure reported
in Section 4.13, gave 2,3-O-isopropylidene-5-[(tert-butoxycarbonyl)-l-homocysteine tert-
butyl ester]-4-C-4-methoxyphenyl-D-ribofuranose 18e (α/β, ∼1:9; 7.8 mg, 68%). The
1
major β-anomer had: H NMR δ 1.35 (s, 3H, CH3), 1.41 (s, 3H, CH3), 1.39 and1.41
(2 × s, 2 × 9H, t-Bu), 1.75–1.89 (m, 1H, H8), 1.95–2.05 (m, 1H, H8’), 2.48–2.54 (m, 2H,
H7,7’), 3.01 (d, J = 14.8 Hz, 1H, H5), 3.20 (d, J = 15.1 Hz, 1H, H5’), 3.80 (s, 3H, CH3O),
4.20–4.25 (m, 1H, H9), 4.65 (d, J = 5.8 Hz, 1H, H3), 4.85 (d, J = 5.8 Hz, 1H, H2), 5.01 (d,
J = 8.1 Hz 1H, NH), 5.40 (s, 1H, H1), 6.82 (d, J = 8.8 Hz, 2H, Ar), 7.12 (d, J = 9.0 Hz,
2H, Ar), [the minor α-anomer had a peak for H1 at δ 5.60 (d, J = 3.8 Hz)]; HRMS calcd
for C28H43NO9SNa+ [M+Na]+ 592.2551, found 592.2522. Step b. Treatment of 18e (α/β,
∼1:9; 7.6 mg, 0.013 mmol) with in TFA (1 mL), using the procedure reported in Section
4.12, gave 19e (α/β, ∼1:9; 3.7 mg, 77%). The major isomer had: 1H NMR (MeOH-d4) δ
1.90–2.00 (m, 2H, H8,8’), 2.48–2.58 (m, 2H, H7,7’), 3.01 (d, J = 14.8 Hz, 1H, H5), 3.20
(d, J = 15.1 Hz, 1H, H5’), 3.80 (s, 3H, CH3O), 4.15 (d, J = 5.8 Hz, 1H, H2), 4.20–4.25 (m,
1H, H9), 4.40 (d, J = 5.8 Hz, 1H, H3), 5.45 (s, H1, 1H), 6.82 (d, J = 8.8 Hz, 2H, Ar), 7.12
(d, J = 9.0 Hz, 2H, Ar); 13C NMR (MeOH-d4) δ 27.51 (C7), 29.70 (C8), 52.52 (C9), 55.33
(CH3O), 42.20 (C5), 72.61 (C3),74.40 (C2), 85.40 (C4), 101.10 (C1), 117.20, 125.81, 127.00,
162.28 (Ar), 172.3 (C10). HRMS calcd for C16H23NO7SNa+ [M+Na]+ 396.1087, found
396.1062.

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Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was partially supported by NIGMS/NCI [1SC1CA138176]. We thank the NIH MARC
U*STAR (GM083688) program for the fellowship to DL and University of Wroclaw and EU social
funds for supporting KSS and JN summer internship training at FIU.
ORCID
Cesar Gonzalez http://orcid.org/0000-0003-0818-5671
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