Total synthesis of the phenolic glycolipid mycoside B and the glycosylated p-hydroxybenzoic acid methyl ester HBAD-I, virulence markers of mycobacterium tuberculosis

Article abstract of DOI:10.1002/ejoc.201300437

The phenolic glycolipid mycoside B, present in Mycobacterium bovis and hypervirulent strains of Mycobacterium tuberculosis, has been synthesized for the first time. Multiple methyl groups were introduced by the extensive use of catalytic asymmetric 1,4-addition reactions, asymmetric hydrogenation of a β-keto ester afforded the basis for the central 1,3-diol moiety, and introduction of the 2-O-methyl-α-L-rhamnoside unit was achieved by stereoselective glycosylation with p-iodophenol and subsequent Sonogashira coupling, providing a basis for the generation of analogues. In addition, the related monosaccharide HBAD-I, present in the same species, has been efficiently synthesized for the first time by selective methylation of the hydroxy group at C-2 of a rhamnoside. The phenolic glycolipid mycoside B and the related phenolic glycoside HBAD-I from Mycobacterium tuberculosis have been synthesized for the first time. A highly convergent strategy was used featuring catalytic asymmetric 1,4-additions of MeMgBr and Me₂Zn and a late-stage Sonogashira coupling as the key steps. Copyright

Full text of DOI:10.1002/ejoc.201300437

FULL PAPER
DOI: 10.1002/ejoc.201300437
Total Synthesis of the Phenolic Glycolipid Mycoside B and the Glycosylated p-
Hydroxybenzoic Acid Methyl Ester HBAD-I, Virulence Markers of
Mycobacterium tuberculosis
Santiago Barroso,[a] Danny Geerdink,[a] Bjorn ter Horst,[a] Eva Casas-Arce,[a] and
Adriaan J. Minnaard*[a]
Keywords: Natural products / Carbohydrates / Glycolipids / Asymmetric synthesis / Total synthesis
The phenolic glycolipid mycoside B, present in Mycobacte-
rium bovis and hypervirulent strains of Mycobacterium
tuberculosis, has been synthesized for the first time. Multiple
methyl groups were introduced by the extensive use of cata-
rhamnoside unit was achieved by stereoselective glycosyl-
ation with p-iodophenol and subsequent Sonogashira cou-
pling, providing a basis for the generation of analogues. In
addition, the related monosaccharide HBAD-I, present in the
lytic asymmetric 1,4-addition reactions, asymmetric hydro- same species, has been efficiently synthesized for the first
genation of a β-keto ester afforded the basis for the central
1,3-diol moiety, and introduction of the 2-O-methyl-α-L-
time by selective methylation of the hydroxy group at C-2 of
a rhamnoside.
among the most specific virulence factors and permit the
strain causing an infection to be deduced and discrimi-
nation between recent infection and vaccination. Further-
more, it has been shown that not all Mycobacterium bovis
BCG strains used for vaccination are able to produce myco-
side B and phthiocerol dimycocerosates (PDIMs), providing
a correlation between the ability to produce these com-
pounds and the risk of complications after vaccination ob-
served in clinical studies.[8] In this regard, an enzyme-linked
immunosorbent assay (ELISA) based on PGLs has recently
shown potential for the diagnosis of TB in HIV-infected
patients.[9] In addition, a lipidomic platform has been estab-
lished for the chemotaxonomic analysis of M. tuberculo-
sis.[10]
The variation in the structures of the different mycobac-
terial PGLs mainly resides in the glycosyl terminus. Differ-
ences in occurrence are found between species of the genus,
but also occur within strains of the same species. For exam-
ple, minor PGLs, different to mycoside B and PGL-tb1,
have been found in some strains of M. tuberculosis, which
has biological implications.[11] Because access to pure,
chemically synthesized PGLs is crucial for reliable immuno-
logical studies, a synthetic strategy to readily obtain with
minimal changes the different PGLs is desirable. We re-
cently communicated the first total synthesis of trisac-
charide PGL-tb.[12] The key elements of the strategy are the
modularity, the high control over the stereoselectivity, and
the introduction of the glycosyl moiety (the most variable
part of the PGLs) by a late-stage Sonogashira reaction.
Here, a full account of this work is presented combined
with a second application of this strategy to the synthesis
of mycoside B.
Introduction
Tuberculosis (TB) is today still one of the most impor-
tant infectious diseases. Although antibiotics and a vaccine
(Bacillus Calmette–Guérin, BCG) are available, the number
of cases reveals that the disease continues to be a global
problem: 8 million casualties and 1.5 million deaths every
year.[1] The synergy with HIV and the advent of new multi-
drug-resistant and hypervirulent strains poses additional
threats.[2] Mycobacterium tuberculosis (M. tuberculosis) is
the most prominent cause of TB, but the related species,
Mycobacterium bovis (M. bovis), can also cause the disease.
The disclosure of the full genome sequence of M. tuber-
culosis H37Rv[3] has allowed scientists to identify the en-
zymes involved in the biosynthesis and transport of second-
ary metabolites that are important in host–pathogen inter-
actions. Furthermore, knockout experiments have shed light
on the specific role of a number of these compounds. The
most prominent representatives are the complex methyl-
branched lipids with long alkyl chains, often glycosylated.[4]
This is also the case in the phenolic glycolipids (PGLs),
which are suspected of being involved in the hypervirulence
of specific mycobacterial strains.[5]
Monoglycosylated mycoside B (Figure 1, 1) is the major
PGL in M. bovis.[6] This compound is also found as a minor
PGL in some specific strains of M. tuberculosis[6c] in which
triglycosyl PGL-tb1 is the predominant species.[7] PGLs are
[a] Stratingh Institute for Chemistry, University of Groningen,
Nijenborgh 7, 9747 AG, Groningen, The Netherlands
E-mail: a.j.minnaard@rug.nl
Homepage: http://www.rug.nl/fmns-research/stratingh
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300437.
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Total Synthesis of Mycoside B and HBAD-I
Figure 1. Related PDIM, PGLs, and p-HBAD found in M. tuberculosis. and M. bovis.
Aryl rhamnoside HBAD-I (2, Figure 1) is clearly closely mutations in pks15/1 are responsible for the lack of phenolic
related to mycoside B. The compound has been detected in glyclolipids in PGL-deficient M. tuberculosis strains. Glyc-
the culture medium of all reference strains of M. tuberculo- osylation is achieved by the use of Rv2962c encoded enzymes
sis and M. bovis.[13] According to Daffé and co-workers, p- in the final step of the biosynthesis of both 1 and 2.
hydroxybenzoic acid is the precursor of both 1 and 2. How-
Note, the secretion of methyl benzoate 2 and its analogue
ever, it is remarkable that 2 and its acid form are not precur- triglycosyl methyl benzoate appears to be highly relevant.
sors of 1. Thus, compound 2 is a final metabolite of both Studies with knockout bacteria have shown that the in-
mycobacteria. Concerning the biosynthesis of these com- hibited production of some or all p-HBADs is inter-related
pounds, Daffé and co-workers proposed that the Pks15/1 to an increased secretion of pro-inflammatory cytokines.[15]
gene is responsible for the elongation of the p-hydroxyben- In other words, p-HBADs seem to attenuate the immune
zoic acid to form a p-hydroxyphenylalkanoate.[13,14] The lat- response of the host. Given the immunological interest and
ter compound is transformed by the gene PpsA-E into the the connection of 2 to mycoside B, we decided to synthesize
phenolphthiocerol unit. Daffé and co-workers disclosed that 2 as well.
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ety was planned for the last-but-one step of our synthesis,
due to the precious nature of the all-R-tetramethyl-
Results and Discussion
The dissimilar nature of the different parts of mycoside B branched acid 4. Finally, concomitant reduction of the tri-
calls for a strongly convergent synthetic strategy. The retro- ple bond and hydrogenolysis of the benzyl protecting
synthesis we devised for mycoside B (1) parallels the one groups should deliver mycoside B.
used in the synthesis of PGL-tb1 and divides this complex
In parallel with the synthesis of PDIM-A and PGL-tb1,
molecule into three main building blocks: rhamnoside 3, the synthesis of mycoside B commenced with building
mycocerosic acid (4), and diol 5, as summarized in block 6 (Scheme 2).[12,18] Thus, 2-cycloheptenone (6) was
Scheme 1.
transformed into 9 in a one-pot catalytic asymmetric 1,4-
The first of these units, 2-O-methyl-α-l-rhamnoside 3, addition of Me2Zn followed by in situ alkylation with iodo-
appropriately benzylated (see above), is equipped with a p- ethane. Use of a catalyst prepared in situ from CuII triflate
iodophenol unit. This functionalization allows the carbo- and a chiral phosphoramidite ligand (Feringa’s ligand) af-
hydrate to be installed through a Sonogashira coupling re- forded 9 in an er of 97.5:2.5.[19] The dr of the alkylation is
action instead of by glycosylation.[16] In our view, this Ͼ20:1, considerably higher than generally observed in the
should simplify the connection of the carbohydrate to the corresponding six-membered-ring systems.[20] We have also
lipid chain. No less important, the α configuration at the noted these excellent diastereoselectivities previously in
anomeric center could exclusively be ensured at an earlier eight-membered-ring systems.[21]
stage of the synthesis. stereospecific Baeyer–Villiger reaction served to insert the
A regioselective and
The synthesis of building block 5 faces two main oxygen at the stereogenic center bearing the ethyl substitu-
challenges. One is the selective generation of the different ent. Despite extensive experimentation, the best result ob-
stereocenters, there being a significant distance between tained with the Baeyer–Villiger reaction was a moderate
them. To solve this problem we relied on a one-pot 1,4- 60% yield, achieved by using mCPBA. Undoubtly this out-
addition/alkylation reaction by using 2-cycloheptenone (6) come is due to the increase in ring strain incurred on pro-
as the starting material. The aforementioned approach pro- gressing from a seven- to an eight-membered ring, which
vides the first two stereocenters on the right hand of the renders the C-to-O shift in the reaction unfavorable. Versa-
molecule and bridges the gap between these and the anti- tile solutions to this problem are scarce, and also enzymatic
1,3-diol unit, in turn prepared by asymmetric RuII-cata- Baeyer–Villiger reactions are invariably carried out on six-
lyzed hydrogenation of a β-keto ester followed by alkylation membered-ring systems or substrates for which ring strain
and subsequent reduction.
is relieved. An accompanying problem is that more reactive
The other challenge encountered in 5 is the 16-carbon congeners of mCPBA raise safety concerns.[22] After meth-
spacer that has to connect the 1,3-diol moiety with the aro- anolysis of 10, methyl ester 11 was O-methylated to give
matic ring in rhamnoside 3. It was found that such an α,ω- ester 12, thereby completing the construction of the right-
difunctionalized alkyl chain suitable for a Sonogashira reac- hand side of 5.
tion was readily accessible from commercially available al-
kynol 7.
Ther reduction of 12 with DIBAL-H gave directly alde-
hyde 13, which was smoothly transformed into intermediate
The third main block, mycocerosic acid (4), is one of β-keto ester 14 by using ethyl diazoacetate and 5 mol-% of
several methyl-branched fatty acids from M. tuberculosis NbCl5 as catalyst.[23] This opened the door for the antici-
that we have synthesized over the years by using an iterative pated asymmetric hydrogenation.[24] By using 1 mol-% of
protocol comprising catalytic asymmetric conjugate ad- (R)-[{RuCl(tol-BINAP)}2(μ-Cl)3][NH2Me2] and a hydrogen
dition, reduction, and Horner–Wadsworth–Emmons ole- pressure of 20 bar, we were rewarded with β-hydroxy ester
fination.[17] Conveniently, esterification of the 1,3-diol moi- 15 in good yield and with an excellent stereoselectivity
Scheme 1. Retrosynthetic analysis of mycoside B.
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Total Synthesis of Mycoside B and HBAD-I
Scheme 2. Reagents and conditions: a) Cu(OTf)2 (0.5 mol-%), (S,R,R)-phosphoramidite (1 mol-%), Me2Zn, toluene, –25 °C; then EtI,
HMPA, 0 °C, 83%, Ͼ20:1 dr trans/cis, 97.5:2.5 er (for trans); b) mCPBA, CH2Cl2, reflux, 60%; c) K2CO3, MeOH, room temp., 90%;
d) NaH, MeI, DMF, room temp., 92%; e) DIBAL-H, Et2O, –84 °C, 86%; f) ethyl diazoacetate, NbCl5 (5 mol-%), CH2Cl2, 86%; g) (R)-
[{RuCl(tol-BINAP)}2(μ-Cl)3][NH2Me2] (1 mol-%), 20 bar H2, EtOH, room temp., 76%, dr Ͼ99:1; h) AlMe3, MeNH(OMe)·HCl, THF,
73%. HMPA = hexamethylphosphoramide, mCPBA = m-chloroperbenzoic acid, DIBAL-H = diisobutylaluminium hydride.
(Ͼ99:1 dr). Treatment of ester 15 with AlMe3 and N,O-
The addition of 20, after the formation of the corre-
dimethylhydroxylamine afforded Weinreb amide 16 in 76% sponding alkyl Li reagent, to Weinreb amide 16 turned out
yield, a better result than that obtained by using the corre- not to be trivial (Scheme 4). First, a stepwise procedure
sponding lithium amide.
with initial deprotonation of the hydroxy group in 16 was
The installation of the long spacer of mycoside B was investigated. The deprotonation is important as it avoids
preceded by a four-step synthesis of building block 20, as elimination to the corresponding unsaturated amide. The
depicted in Scheme 3. Despite the potential of the alkyne use of NaH and tBuMgCl proved to be inconvenient. How-
zipper reaction to afford α,ω-bifunctionalized aliphatic ever, tBuLi could be used for this purpose as long as the
chains of different lengths, its application to natural prod- amount of base did not exceed 1 equiv., otherwise the excess
uct synthesis has been very infrequent since its introduction reagent formed a tert-butyl ketone by nucleophilic attack
by Brown and Yamashita in 1975.[25,26] Here we used the on the amide. At the same time, tBuLi was used to lithiate
reaction to shift the triple bond in commercially available 20 by Li/halogen exchange. For this reason, the added
alkyne 7 to the terminal position (compound 17). Further amount of tBuLi for the exchange had to be carefully con-
elaboration involved TMS-protection of the acetylide unit, trolled to prevent any excess leading to the undesired for-
tosylation of the hydroxy group, and nucleophilic displace- mation of the inseparable tert-butyl ketone. Optimization
ment with NaI, providing alkyne iodide 20 in a good overall showed that a ratio of 20/tBuLi of 1:1.6 for the lithiation
yield.
avoided that problem. For reasons of simplification and ro-
Scheme 3. Reagents and conditions: a) NaH, 1,3-diaminopropane, 70 °C, 61%; b) nBuLi, TMSCl, THF, –40 °C to room temp., 92%;
c) pTsCl, pyridine, CHCl3, room temp., 87%; d) NaI, acetone, room temp., 86%.
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Scheme 4. Reagents and conditions: a) 20, tBuLi, Et2O, –84 °C, 2 h, then amide 16, 81%; b) NH4BH(OAc)3, MeCN, AcOH, THF, –25 °C,
75%; c) MeOH, K2CO3, room temp., quant. TMS = trimethylsilyl, pTsCl = p-toluenesulfonyl chloride.
bustness, we finally decided to discard the stepwise process group had to be removed. Stirring 22 in MeOH/K2CO3
and use an excess of lithiated 20 for both deprotonation completed this step to give the central building block 5 in
and alkylation. After extensive optimization, we were very quantitative yield.
pleased to see the exclusive formation of the desired β-
At this point we turned our attention to the synthesis of
hydroxy ketone 21 in 81% yield.
rhamnoside 3. The major challenge was to selectively meth-
Having both defined the third stereocenter and installed ylate the hydroxy group at C-2. This was achieved by a
the spacer, the 1,3-diol in the required anti configuration strategy reported by Fürstner and Müller (Scheme 5).[30]
had to be prepared from the β-hydroxycarbonyl moiety.[27] Peracetylation of l-rhamnose was followed by the forma-
Initially we applied the method reported recently by tion of rhamnosyl bromide and subsequent reflux in eth-
Phansavath and co-workers by diastereoselective hydrogen- anol with sym-collidine as an acid scavenger to provide or-
ation with catalytic RuCl3 and PPh3.[28] Although this pro- thoester 25. One-pot acetate hydrolysis and benzylation of
vided the desired anti-diol, it also unfortunately resulted in the hydroxy groups at C-3 and C-4 provided 26, which,
concomitant reduction of the triple bond. Fortunately, the upon acidic hydrolysis, afforded a mixture of acetates 27 at
methodology of Evans and Chapman using NH4BH- C-1 and C-2. Separation was not necessary because under
(OAc)3 gave 22 in good yield.[29] The solvent for the reac- the conditions used for the formation of trichloroacetimid-
tion had to be adapted to secure sufficient solubility. With ate 28, both acetates rapidly interconvert, but only the
a view to the subsequent Sonogashira reaction, the TMS rhamnoside with the acetate at C-2 is transformed into 28.
Scheme 5. Reagents and conditions: a) Ac2O, pyridine, room temp., 98%; b) HBr in AcOH, Ac2O; c) sym-collidine, EtOH, Bu4NI, 80 °C,
8 h, 66% over both steps; d) BnBr, KOH, THF, reflux, 8 h, 78%; e) HOAc/H2O (4:1), room temp., 16 h, 90%; f) Cl3CCN, cat. NaH,
CH2Cl2, 75% α + 11% β; g) 4-iodophenol, TMSOTf, CH2Cl2, –45 °C to room temp., 90%; h) MeONa, MeOH, room temp., 87%; i) MeI,
NaH, DMF, 0 °C, 95%. TMSOTf = trimethylsilyl trifluoromethanesulfonate.
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Total Synthesis of Mycoside B and HBAD-I
Although the formation of 28 has previously been achieved with simultaneous removal of both benzyl protecting
with Cs2CO3 as a catalyst, we were not satisfied with the groups in the final step. In this way, mycoside B was pre-
reported yield. The use of NaH as base greatly improved pared in 14 steps in an overall yield of 4.3% (linear se-
the yield and gave 28 as an 87:13 mixture of α and β ano- quence starting from cycloheptenone 6). Full analysis of the
mers in 86% yield.[31]
resulting compound by NMR spectroscopy, MS, and op-
The next step was the glycosylation of 28 with 4-iodo- tical rotation showed 1 to be identical to natural mycoside
phenol. A high α selectivity was ensured by participation of B.[6]
the acetyl group at C-2, which afforded 29 in 90% yield.
With the experience gained in the synthesis of building
Although we chose to use pure 28α for the glycosylation, block 3, a synthetic route to p-HBAD-I (2) was planned.
28β can also be used in this step with a similar result. Fi- Most likely, methoxycarbonylation of 3 followed by debenz-
nally, the 2-acetyl group was methanolyzed and the re- ylation would provide 2. However, orthogonal protection
sulting hydroxy function methylated to give 3 in high yield. with benzyl groups, as in the synthesis of mycoside B, was
With both 5 and 3 in hand we proceeded with the Sono- not required in the synthesis of p-HBAD-I. Therefore we
gashira reaction, a key step in our synthesis (Scheme 6). opted for an alternative and more efficient synthesis.
Pleasingly, the use of catalytic [PdCl2(PPh3)2] and CuI gave
31 in 91% yield.
Again, methylation at O-2 was the key and for this, selec-
tive protection of 3-OH and 4-OH was required. Unfortu-
The synthesis of mycocerosic acid (4) in 12% yield over nately, methods that simultaneously protect two hydroxy
15 steps has previously been reported by our group.[17c] Our groups in l-rhamnose-like acetals and orthoesters lead to
methodology for the stereoselective synthesis of 1,3-methyl cis-fused five-membered rings involving O-2 and O-3. Pro-
arrays was based on an iterative protocol. The first step tection of diequatorial trans-1,2-diols with 1,2-diacetals ac-
involves a highly enantioselective Cu-catalyzed conjugate cording to Ley and co-workers, however, seemed to be a
addition of MeMgBr to an α,β-unsaturated thioester (start- perfect alternative to protect 3-OH and 4-OH.[32] To achieve
ing with achiral compound 8). The reduction of the thioes- this, Frost modification of Ley’s methodology using 2,2,3,3-
ter to its aldehyde followed by olefination elongates the tetramethoxybutane was most convenient in terms of cost,
chain and leads to a new α,β-unsaturated thioester. For this ease of preparation, and selectivity.[33]
synthesis of mycocerosic acid we applied the refinements
Therefore peracetylated l-rhamnose 23 was subjected to
developed in the synthesis of mycolipenic acid, using DI- BF3·OEt2-mediated glycosylation with methyl p-hydroxy-
BAL-H for the reduction (replacing the Pd/C/Et3SiH sys- benzoate (Scheme 7). Upon removal of the acetyl groups,
tem) and Horner–Wadsworth–Emmons instead of Wittig triol 34 was successfully protected at O-3 and O-4 with
olefinations.[17d,17e]
2,2,3,3-tetramethoxybutane, and O-2 was subsequently
Esterification of 31 with mycocerosic acid (4) was ac- methylated. Both the protection and methylation steps were
complished by employing EDC and DMAP in a moderate carried out in a convenient one-pot procedure in a moder-
but acceptable 60% yield. As planned, the triple bond in ate 43% yield.[34] Treatment with TFA/water afforded the
ester 32 was completely reduced with Pd/C and 1 bar of H2 desired p-HBAD-I (2) in 50% yield. In retrospect, this
Scheme 6. Reagents and conditions: a) [PdCl2(PPh3)2] (5 mol-%), PPh3 (5 mol-%), CuI (10 mol-%), Et3N, 40 °C, 91%; b) EDC·HCl,
DMAP, CDCl3, 62%; c) Pd/C, 1 bar H2, EtOAc, EtOH, room temp., 76%. EDC·HCl = N-(3-dimethylaminopropyl)-NЈ-ethylcarbodiimide
hydrochloride, DMAP = 4-(dimethylamino)pyridine, TMS = trimethylsilyl.
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Scheme 7. Reagents and conditions: a) Ac2O, pyridine, room temp., 98%; b) methyl 4-hydroxybenzoate, BF3·OEt2, room temp., 18 h,
72%; c) MeONa, MeOH, room temp., 94%; d) i. CH3CN, 2,2,3,3-tetramethoxybutane, BF3·OEt2, 0 °C; ii. NaH, MeI, 0 °C, 43%; e) TFA/
water 9:1, 50%.
1H and 13C NMR spectra were recorded with a Varian AMX400
route, comprising only five steps, could function as an alter-
or 400-MR spectrometer (400 and 100.59 MHz, respectively) using
CDCl3 or CD3OD as solvent, unless stated otherwise. Chemical
native to the synthesis of building block 3, requiring only
benzylation at O-3 and O-4. Increasing the yield of the se-
quence 34Ǟ35Ǟ3 requires attention, however.
shifts are reported in ppm with the solvent resonance as the in-
ternal standard (CHCl3: δ = 7.26 ppm for 1H, δ = 77.0 ppm for
1
13C; CD3OD: δ = 3.31 ppm for H). Data are reported as follows:
chemical shift (δ), multiplicity (s = singlet, d = doublet, dd = double
doublet, td = triple doublet, t = triplet, q = quartet, br. = broad,
Conclusions
m = multiplet), coupling constants J, and integration. Due to the
(multiple) long alkyl chains in some of the compounds, we were
not able to resolve all the individual 13C signals in the spectra.
High-resolution mass spectra were recorded with a Thermo Scien-
tific LTQ Orbitrap. Optical rotations were measured with a Propol
automatic polarimeter (sodium D line, λ = 589 nm). HPLC analysis
was performed with a Chiralcel AD 250ϫ4.6 mm column with an
ELS detector (ELSD).
A first synthesis of mycoside B (1) has been achieved.
The approach provides full stereocontrol; Cu-catalyzed
asymmetric conjugate addition of MeMgBr and Me2Zn in-
troduces the methyl groups into the mycocerosic acid and
the phthiocerol chain and RuII-catalyzed stereoselective hy-
drogenation followed by anti reduction defines the stereo-
chemistry of the 1,3-diol. In the final stages of the synthesis,
Sonogashira cross-coupling proved to be a versatile tool for
connecting the glycosyl moiety. Taken together, this demon-
strates the applicability of our approach to the synthesis of
PGL-tb1 and mycoside B and therefore could be applied
to the synthesis of other PGLs found in mycobacteria. In
addition, p-HBAD-I (2) has been synthesized for the first
time. Ley-type protection provides the desired compound in
only five steps from rhamnose, and this should elicit further
studies on the role of this compound in the attenuation of
the host immune response.
Flash chromatography was performed by using SiliCycle SiliaFlash
P60 (230–400 mesh), as obtained from Screening Devices, or by
automated column chromatography using a Reveleris flash system
purchased from Grace Davison Discovery Sciences. TLC analysis
was performed on Merck silica gel 60/Kieselguhr F254 (0.25 mm).
Compounds were visualized by using either Seebach’s reagent [a
mixture of phosphomolybdic acid (25 g), cerium(IV) sulfate (7.5 g),
H2O (500 mL), and H2SO4 (25 mL)] or a KMnO4 stain [K2CO3
(40 g), KMnO4 (6 g), H2O (600 mL), and 10% NaOH (5 mL)].
(6S,7R)-7-Methoxy-6-methylnonanal (13): For the complete synthe-
sis of building block 12 from 2-cyclohepten-1-one (6), see ref.[18]
Diisobutylaluminium hydride (1 m in CH2Cl2, 4.33 mL, 4.33 mmol)
was added dropwise to a stirred solution of methyl (6S,7R)-7-meth-
oxy-6-methylnonanoate (12;[18] (780 mg, 3.61 mmol) in Et2O
(10 mL) at –84 °C under nitrogen. After completion of the reaction
(20 min), as indicated by TLC (pentane/Et2O, 85:15), a few drops
of MeOH were added to quench the reaction and the solution was
warmed to room temp. A saturated solution of Rochelle’s salt
(3 mL) was added and the mixture was stirred for 30 min. Then the
reaction mixture was diluted with Et2O (40 mL), the layers were
separated and the organic layer was washed with brine (5 mL) and
dried (Na2SO4). The solvent was removed under reduced pressure
Experimental Section
All reactions were performed by using oven- or flame-dried glass-
ware and dry solvents. Solvents were distilled prior to use: MTBE,
Et2O, and THF over Na/benzophenone, and CH2Cl2 over CaH2.
All other reagents were purchased from Sigma–Aldrich, Acros, TCI
Europe, Alfa Aesar, Merck, and Apollo Scientific, and used with-
out further purification unless noted otherwise. Grignard and
organolithium reagents were titrated by using sBuOH and catalytic
amounts of 1,10-phenanthroline. All moisture-sensitive reactions
were performed under nitrogen.
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Total Synthesis of Mycoside B and HBAD-I
and the product was purified by flash chromatography to give alde-
EtOAc (100 mL) and 2 m aq. NaOH (5 mL) were added. The or-
hyde 13 (560 mg, 3.01 mmol, 89% yield) as a colorless oil together ganic layer was separated and the aqueous layer extracted with
with a small amount of the related alcohol (18 mg, 3% yield). The
EtOAc (2ϫ 20 mL). The combined organic extracts were washed
with water (10 mL) and brine (10 mL), and then dried (Na2SO4).
The solvent was removed under reduced pressure and the product
was purified by flash chromatography to give 16 (382 mg,
1.32 mmol, 73% yield) as a colorless oil.
spectroscopic data were in agreement with a previous report.[18]
Ethyl (8S,9R)-9-Methoxy-8-methyl-3-oxoundecanoate (14): NbCl5
(38.9 mg, 0.144 mmol) was added to a stirred solution of aldehyde
13 (536 mg, 2.88 mmol) in CH2Cl2 (30 mL) under nitrogen. After
1
5 min, ethyl diazoacetate (0.527 mL, 4.32 mmol) was added drop- [α]2D2 = –48.6 (c = 1.0, CHCl3). H NMR (400 MHz, CDCl3): δ =
wise to the solution, taking care with the gas evolution. After com-
pletion of the reaction (2 h), as indicated by TLC (pentane/Et2O,
85:15), the reaction mixture was mixed with water (30 mL). The
organic layer was separated and the aqueous layer extracted with
CH2Cl2 (2ϫ 10 mL). The combined organic extracts were washed
with brine (10 mL) and dried (Na2SO4). The CH2Cl2 was removed
under reduced pressure and the product was purified by flash
chromatography to give 14 (677 mg, 2.49 mmol, 86% yield) as a
colorless oil. [α]2D2 = –4.0 (c = 1.0, CHCl3). 1H NMR (400 MHz,
CDCl3): δ = 4.16 (q, J = 7.1 Hz, 2 H), 3.40 (s, 3 H), 3.30 (s, 1 H),
2.82 (ddd, J = 7.4, 5.3, 4.1 Hz, 2 H), 2.51 (t, J = 7.3 Hz, 1 H),
1.70–1.51 (m, 5 H), 1.48–1.29 (m, 2 H), 1.25 (t, J = 7.1 Hz, 3 H),
1.28–1.14 (m, 2 H), 1.06 (m, 1 H), 0.87 (t, J = 7.4 Hz, 3 H), 0.79
(d, J = 6.8 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 202.8
(s), 167.2 (s), 86.5 (d), 61.3 (t), 57.3 (q), 49.2 (t), 42.9 (t), 34.6 (d),
32.3 (t), 26.9 (t), 23.7 (t), 22.3 (t), 14.7 (q), 14.0 (q), 9.9 (q) ppm.
HRMS (ESI+): calcd. for C15H28O4Na [M + Na]+ 295.1885; found
295.1866.
4.01 (m, 1 H), 3.77 (s, 1 H), 3.68 (s, 3 H), 3.33 (s, 3 H), 3.19 (s, 3
H), 2.86 (ddd, J = 7.6, 5.0, 4.0 Hz, 1 H), 2.66 (d, J = 16.6 Hz, 1
H), 2.43 (dd, J = 17.0, 9.7 Hz, 1 H), 1.69 (d, J = 6.6 Hz, 1 H),
1.61–1.17 (m, 12 H), 1.17–1.04 (m, 1 H), 0.90 (t, J = 7.4 Hz, 3 H),
0.82 (d, J = 6.8 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3): δ =
173.6 (s), 86.4 (d), 67.6 (d), 61.0 (q), 57.1 (q), 38.0 (t), 36.4 (t), 34.5
(d), 32.4 (t), 31.5 (q), 27.3 (t), 25.6 (t), 22.1 (t), 14.5 (q), 9.8 (q) ppm.
HRMS (ESI+): calcd. for C15H32NO4 [M + H]+ 290.2331; found
290.2314.
Hexadec-15-yn-1-ol (17): NaH (60% in mineral oil, 6.41 g,
147 mmol) was washed with pentane and carefully added to a flask
containing 1,3-diaminopropane (70 mL, highly hygroscopic!). The
mixture was heated at 50 °C until it became clear (approx. 1 h).
Then the mixture was cooled to room temp. and alkyne 7 (5.0 g,
21 mmol) was added. The mixture was then heated to 69 °C and
stirred for 24 h. It was then poured into a beaker containing ice/
water and extracted with Et2O (3ϫ 75 mL). The combined organic
extracts were washed with 0.1 m aq. HCl (30 mL), brine, and dried
(Na2SO4). The solvent was removed under reduced pressure and
the product purified by flash chromatography to give 17 (3.05 g,
12.8 mmol, 61% yield) as a white solid. The spectroscopic data
were in agreement with the literature.[35] 1H NMR (400 MHz,
CDCl3): δ = 3.60 (t, J = 6.7 Hz, 2 H), 2.15 (dt, J = 2.6, J = 7.1 Hz,
2 H), 1.91 (t, J = 2.6 Hz, 1 H), 1.67 (s, 1 H), 1.52 (m, 4 H), 1.38–
1.24 (m, 20 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 84.6 (s),
67.9 (d), 62.8 (t), 32.6 (t), 29.56 (t), 29.54 (t), 29.52 (t), 29.43 (t),
29.37 (t), 29.03 (t), 28.6 (t), 28.4 (t), 25.6 (t), 18.3 (t) ppm.
Ethyl (3R,8S,9R)-3-Hydroxy-9-methoxy-8-methylundecanoate (15):
(R)-[{RuCl(tol-BINAP)}2(μ-Cl)3][NH2Me2] (34.4 mg, 0.019 mmol)
was added to a solution of keto ester 14 (525 mg, 1.93 mmol) in
degassed EtOH (10 mL) under nitrogen. This solution was placed
in an autoclave and purged with N2 and H2. Hydrogen was intro-
duced (20 bar) and the reaction mixture was stirred at room temp.
overnight. After the hydrogen pressure was released, toluene
(20 mL) was added and the solution was concentrated under re-
duced pressure to remove most of the ethanol. The resulting mix-
ture was directly purified by flash chromatography to give 15
(400 mg, 1.46 mmol, 76% yield) as a colorless oil. [α]2D2 = –15.8 (c
= 1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 4.13 (q, J =
7.1 Hz, 2 H), 3.96 (m, 1 H), 3.29 (s, 3 H), 3.01 (d, J = 3.8 Hz, 1
H), 2.82 (ddd, J = 7.7, 5.1, 4.0 Hz, 1 H), 2.46 (dd, J = 16.3, 3.3 Hz,
1 H), 2.35 (dd, J = 16.4, 8.9 Hz, 1 H), 1.75–1.57 (m, 1 H), 1.55–
1.27 (m, 7 H), 1.23 (t, J = 7.1 Hz, 3 H), 1.30–1.10 (m, 2 H), 1.11–
0.97 (m, 1 H), 0.87 (t, J = 7.4 Hz, 3 H), 0.79 (d, J = 6.9 Hz, 3
H) ppm. 13C NMR (101 MHz, CDCl3): δ = 173.0 (s), 88.1 (d), 67.9
(d), 60.5 (t), 57.3 (q), 41.3 (t), 36.5 (t), 34.7 (d), 32.5 (t), 27.4 (t),
25.7 (t), 22.3 (t), 14.7 (q), 14.1 (q), 10.0 (q) ppm. HRMS (ESI+):
calcd. for C15H31O4 [M + H]+ 275.2217; found 275.2205.
16-(Trimethylsilyl)hexadec-15-yn-1-ol (18): nBuLi (1.6 m, 15.7 mL,
25.1 mmol) was added to a solution of alkynol 17 (2.72 g,
11.4 mmol) in THF (150 mL) at –45 °C. The mixture was stirred
for 3 h, allowing the reaction to slowly warm to room temp. during
this time. TMSCl (3.2 mL, 25.1 mmol) was then added and the
cloudy mixture became clear in a few minutes. The reaction was
monitored by quenching small samples of the reaction mixture with
Et2O/aq. NH4Cl and analyzing the organic layer by TLC (pentane/
EtOAc, 9:1). When full conversion was observed (TLC, ca. 1.5 h),
aq. HCl (2 m, 5 mL) was added and the mixture was stirred for
30 min. Then most of the THF was removed under reduced pres-
sure, water was added (60 mL), and the mixture was extracted with
EtOAc (3ϫ 20 mL). The solvent was removed under reduced pres-
sure and the product was purified by flash chromatography to give
18 (3.25 g, 10.5 mmol, 92% yield) as a colorless oil. 1H NMR
(400 MHz, CDCl3): δ = 3.62 (t, J = 6.7 Hz, 2 H), 2.19 (t, J =
7.2 Hz, 2 H), 1.58–1.44 (m, 5 H), 1.29 (m, 20 H), 0.13 (s, 9 H) ppm.
13C NMR (101 MHz, CDCl3): δ = 107.8 (s), 84.2 (s), 63.0 (t), 32.8
(t), 29.6 (t), 29.58 (t), 29.56 (t), 29.45 (t), 29.41 (t), 29.04 (t), 28.76
(t), 28.60 (t), 25.7 (t), 19.8 (t), 0.2 (q) ppm. HRMS (ESI+): calcd.
for C19H38OSiNa [M + Na]+ 333.2584; found 333.2581.
A mixture of epimers was obtained for reference by the reduction
of 14 with NaBH4 to determine the diastereoselectiviy of the reac-
tion by chiral HPLC using the following conditions: Chiralcel AD
column, 250ϫ4.6 mm; eluent: heptane/IPA, 95:5; 6.56 min
(major), 6.92 min (minor); de Ͼ99.5%.
(3R,8S,9R)-3-Hydroxy-N,9-dimethoxy-N,8-dimethylundecanamide
(16): A solution of AlMe3 in toluene (2 m, 2.71 mL, 5.41 mmol)
was added to a stirred mixture of N,O-dimethylhydroxylamine hy-
drochloride (528 mg, 5.41 mmol) in THF (15 mL) at 0 °C. The re-
action was stirred for 2 h while warming up slowly to room temp.
Subsequently the reaction was cooled to 0 °C and a solution of
the hydroxy ester 15 (495 mg, 1.80 mmol) was slowly added. After
completion of the reaction, as indicated by TLC (pentane/Et2O,
3:7, 4 h), the reaction was quenched by adding 20% Rochelle’s salt
solution (5 mL) and the mixture was stirred for 30 min. Then
16-(Trimethylsilyl)hexadec-15-ynyl 4-Toluenesulfonate (19): Alkyne
18 (2.3 g, 7.4 mmol) and pyridine (1.8 mL, 22 mmol) were dissolved
in CHCl3 (10 mL) and the mixture stirred at 0 °C. Then, p-tolu-
enesulfonyl chloride (2.82 g, 14.8 mmol) was added and the mixture
was stirred until full conversion was observed by TLC (5 h). Sub-
sequently, the mixture was diluted with Et2O (75 mL) and washed
Eur. J. Org. Chem. 2013, 4642–4654
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4649

A. J. Minnaard et al.
FULL PAPER
with water (10 mL), aq. HCl (2 m, 10 mL), aq. satd. NaHCO3
(10 mL), and brine (10 mL). The organic extract was dried
(MgSO4), the solvent removed under reduced pressure, and the
product purified by flash chromatography to give 19 (3.0 g,
6.5 mmol, 87% yield) as a colorless solid. 1H NMR (400 MHz,
CDCl3): δ = 7.78 (d, J = 8.3 Hz, 2 H), 7.33 (d, J = 8.0 Hz, 2 H),
4.01 (t, J = 6.5 Hz, 2 H), 2.44 (s, 3 H), 2.20 (t, J = 7.2 Hz, 2 H),
was stirred at this temperature for 5.5 h when TLC analysis showed
full conversion (solvents were removed from the TLC spot with a
heat gun before eluting with a pentane/Et2O, 75:25 mixture). Sub-
sequently, the reaction was quenched with an aqueous solution of
Rochelle’s salt (20%, 20 mL) and the mixture stirred at room temp.
for 30 min. Water (300 mL) was then added to the mixture, which
was then extracted with CH2Cl2 (4ϫ 75 mL) and Et2O (75 mL).
1.62 (dt, J = 6.6, J = 13.5 Hz, 2 H), 1.50 (dt, J = 6.6, J = 13.5 Hz, The organic extracts were combined and neutralized by adding
2 H), 1.40–1.21 (m, 20 H), 0.14 (s, 9 H) ppm. 13C NMR (101 MHz, water (30 mL) and solid NaHCO3 until pH Ͼ7. Then the aqueous
CDCl3): δ = 144.5 (s), 133.2 (s), 129.7 (d), 127.8 (d), 107.7 (s), 84.2 layer was separated and the organic layer washed with water
(s), 70.7 (d), 29.58 (d), 29.56 (d), 29.54 (d), 29.45 (d), 29.35 (d),
29.04 (d), 28.89 (d), 28.78 (d), 28.75 (d), 28.59 (d), 25.29 (d), 21.59
(d), 19.8 (d), 0.2 (q) ppm. HRMS (ESI+): calcd. for C26H44O3S-
SiNa [M + Na]+ 487.2678; found 487.2686.
(20 mL) and brine (20 mL) and dried (Na2SO4). The solvent was
removed under reduced pressure and the product purified by flash
chromatography to give compound 22 (360 mg, 0.686 mmol, 75%
yield) as a white waxy solid. [α]2D2 = –4.0 (c = 1.0, CHCl3). 1H NMR
(400 MHz, CDCl3): δ = 3.89 (m, 2 H), 3.31 (s, 3 H), 2.85 (ddd, J
= 7.6, 5.3, 3.9 Hz, 1 H), 2.79 (br. s, 2 H), 2.18 (t, J = 7.2 Hz, 2 H),
1.73–1.60 (m, 1 H), 1.56 (t, J = 5.6 Hz, 2 H), 1.53–1.30 (m, 15 H),
1.33–1.16 (m, 20 H), 1.13–1.01 (m, 1 H), 0.89 (t, J = 7.3 Hz, 3 H),
0.81 (d, J = 6.8 Hz, 3 H), 0.12 (s, 9 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 107.7 (s), 86.7 (d), 84.2 (s), 69.30 (d), 69.25 (d), 57.3
(q), 42.2 (t), 37.45 (t), 37.43 (t), 34.8 (d), 32.6 (t), 29.63 (t), 29.62
(t), 29.60 (t), 29.55 (t), 29.45 (t), 29.03 (t), 28.74 (t), 28.58 (t), 27.5
(t), 26.1 (t), 25.8 (t), 22.3 (t), 19.8 (t), 14.8 (q), 10.0 (q), 0.1 (q) ppm.
HRMS (ESI+): calcd. for C32H64O3SiNa [M + Na]+ 547.4517;
found 547.4514.
(16-Iodohexadec-1-ynyl)trimethylsilane (20): Tosylate 19 (1.71 g,
3.68 mmol) and sodium iodide (1.82 g, 12.1 mmol) were dissolved
in acetone (40 mL) under nitrogen. The mixture was stirred until
full conversion was observed by TLC (48 h). Then the mixture was
diluted in EtOAc (50 mL), most of the acetone was removed under
reduced pressure, and more EtOAc (50 mL) was added. The mix-
ture was washed with aq. Na2S2O3 (10%, 10 mL), water (10 mL),
and brine (10 mL), and then dried (Na2SO4). The solvent was re-
moved under reduced pressure and the product purified to give 20
(1.33 g, 3.16 mmol, 86% yield) as a colorless oil. 1H NMR
(400 MHz, CDCl3): δ = 3.18 (t, J = 7.1 Hz, 2 H), 2.21 (t, J =
7.1 Hz, 2 H), 1.82 (q, J = 7.1 Hz, 2 H), 1.51 (q, J = 7.1 Hz, 2 H),
1.41–1.33 (m, 2 H), 1.31–1.24 (m, 18 H), 0.14 (s, 9 H) ppm. 13C
NMR (101 MHz, CDCl3): δ = 107.7 (q), 84.2 (q), 33.6 (t), 30.5 (t),
29.59 (t), 29.55 (t), 29.52 (t), 29.46 (t), 29.40 (t), 29.05 (t), 28.76 (t),
28.61 (t), 28.52 (t), 19.8 (t), 7.2 (t), 0.18 (q) ppm. HRMS (ESI+):
calcd. for C19H37ISiNa [M + Na]+ 443.1607; found 443.1609.
Note: The hydroxy ketone 21 has low solubility in AcOH/MeCN
at –25 °C and therefore a high dilution was required. The mixture
was not heterogeneous but cloudy, although it was not determined
whether that was because of the low solubility or because AcOH
was freezing.
(3R,4S,9R,11R)-3-Methoxy-4-methylheptacos-26-yne-9,11-diol (5):
K2CO3 (142 mg, 10.3 mmol) was added to a solution of diol 22 in
MeOH (15 mL) and the mixture was stirred overnight at room
temp. Then the mixture was diluted with EtOAc (50 mL), washed
with water (2ϫ 10 mL) and brine (10 mL), and dried (Na2SO4).
The solvent was removed under reduced pressure and the product
purified by short-column flash chromatography to give compound
(3R,4S,9R)-9-Hydroxy-3-methoxy-4-methyl-27-(trimethylsilyl)hept-
acos-26-yn-11-one (21): tBuLi (1.7 m, 3.58 mL, 6.08 mmol) was
added to a stirred solution of iodoalkyne 20 (1.59 g, 3.79 mmol) in
Et2O (40 mL) at –84 °C (EtOAc/liq. N2 bath). After 1 h at this
temperature, a solution of Weinreb amide 16 (332 mg, 1.15 mmol)
in Et2O (20 mL) was added. The mixture was stirred until full con-
version was observed by TLC (1 h). Then a saturated aqueous solu-
tion of NH4Cl (10 mL) was added to quench the reaction. The
mixture was diluted with additional Et2O (20 mL), the aqueous
layer was removed, and the organic layer washed with water
(10 mL) and brine (10 mL). Et2O was removed under reduced pres-
sure and the product purified by flash chromatography to give com-
pound 21 (484 mg, 0.926 mmol, 81% yield) as a colorless oil. [α]2D2
5 (312 mg, 0.689 mmol, quantitative) as a white waxy solid. [α]2D2
=
1
–5.8 (c = 1.0, CHCl3). H NMR (400 MHz, CDCl3): δ = 3.92 (m,
2 H), 3.32 (s, 3 H), 2.86 (ddd, J = 7.7, 5.2, 4.3 Hz, 1 H), 2.40 (s, 2
H), 2.17 (td, J = 7.1, 2.7 Hz, 2 H), 1.92 (t, J = 2.6 Hz, 1 H), 1.73–
1.63 (m, 1 H), 1.59 (t, J = 5.6 Hz, 2 H), 1.45 (dddd, J = 23.6, 21.3,
10.8, 5.0 Hz, 14 H), 1.34–1.16 (m, 21 H), 1.16–1.01 (m, 1 H), 0.90
(t, J = 7.4 Hz, 3 H), 0.82 (d, J = 6.9 Hz, 3 H) ppm. 13C NMR
(101 MHz, CDCl3): δ = 86.7 (d), 84.8 (s), 69.42 (d), 69.37 (d), 68.0
(d), 57.5 (q), 42.3 (t), 37.48 (t), 37.47 (t), 34.8 (d), 32.6 (t), 29.63
(t), 29.58 (t), 29.48 (t), 29.08 (t), 28.7 (t), 28.5 (t), 27.5 (t), 26.1 (t),
25.8 (t), 22.3 (t), 18.4 (t), 14.8 (q), 10.0 (q) ppm. HRMS (ESI+):
calcd. for C29H56O3Na [M + Na]+ 475.4122; found 475.4123.
1
= –13.6 (c = 1.0, CHCl3). H NMR (400 MHz, CDCl3): δ = 4.00
(m, 1 H), 3.31 (s, J = 0.6 Hz, 3 H), 3.07 (s, 1 H), 2.85 (ddd, J =
7.7, 5.2, 4.2 Hz, 1 H), 2.57 (dd, J = 17.4, 2.6 Hz, 1 H), 2.47 (dd, J
= 17.4, 8.9 Hz, 1 H), 2.40 (t, J = 7.4 Hz, 2 H), 2.19 (t, J = 7.1 Hz,
2 H), 1.72–1.62 (m, 1 H), 1.60–1.32 (m, 13 H), 1.31–1.15 (m, 20
H), 1.13–1.01 (m, 1 H), 0.89 (t, J = 7.4 Hz, 3 H), 0.81 (d, J =
6.7 Hz, 3 H), 0.12 (s, 9 H) ppm. 13C NMR (101 MHz, CDCl3): δ
= 212.6 (s), 107.7 (s), 86.6 (d), 84.2 (s), 67.6 (d), 57.3 (q), 48.9 (t),
43.7 (t), 36.4 (t), 34.8 (d), 32.6 (t), 29.59 (t), 29.55 (t), 29.54 (t),
29.44 (t), 29.41 (t), 29.34 (t), 29.13 (t), 29.0 (t), 28.8 (t), 28.6 (t),
27.4 (t), 25.8 (t), 23.6 (t), 22.3 (t), 19.8 (t), 14.8 (q), 10.0 (q), 0.1
(q) ppm. HRMS (ESI+): calcd. for C32H62O3SiNa [M + Na]+
545.4366; found 545.4355.
1,2,3,4-Tetra-O-acetyl-L-rhamnose (23): l-Rhamnose monohydrate
(10.2 g, 62.2 mmol) was dissolved in acetic anhydride (65 mL) and
pyridine (65 mL) and stirred for 16 h. Then, the solvents where
removed under reduced pressure and the crude was purified by
flash chromatography to give 23 (20.2 g, 61.0 mmol, 98% yield) as
a colorless oil.
2-O-Acetyl-3,4-di-O-benzyl-α-
L-rhamnosyl
Trichloroacetimidate
(28α) and 2-O-Acetyl-3,4-di-O-benzyl-β-
L-rhamnosyl Trichloroacet-
(3R,4S,9R,11R)-3-Methoxy-4-methyl-27-(trimethylsilyl)heptacos- imidate (28β): For the complete synthesis of compound 27 from l-
26-yne-9,11-diol (22): Tetramethylammonium triacetoxyborohyd-
ride (1.69 g, 6.43 mmol) was added in portions over 30 min to a
rhamnose, see ref.[30a] Compound 27 (a mixture of 1-O- and 2-O-
acetyl rhamnosides, both α and β anomeric configurations; 11.3 g,
solution of 21 (480 mg, 0.918 mmol) in a mixture of AcOH 29.2 mmol) was dissolved in CH2Cl2 (45 mL). A catalytic amount
(40 mL), MeCN (40 mL), and THF (3 mL) at –25 °C. The mixture of NaH (60% in mineral oil, 100 mg, 2.4 mmol) was added and the
4650
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Eur. J. Org. Chem. 2013, 4642–4654

Total Synthesis of Mycoside B and HBAD-I
mixture was stirred at 0 °C. Then Cl3CCN (20.5 mL, 205 mmol,
7 equiv.) was added and the mixture stirred until consumption of
the starting material (1.5 h). Silica gel (ca. 500 mg) was added to
quench the reaction, and the mixture was filtered and concentrated
under reduced pressure. The product was purified by flash
chromatography to give compound 28α (11.7 g, 22.1 mmol, 75%
yield) and its anomer 28β (1.7 g, 3.2 mmol, 10.9% yield). The spec-
troscopic data are in agreement with those of previous reports for
these compounds.[30]
fied by flash chromatography to give compound 30 (3.32 g,
6.08 mmol, 87% yield) as a colorless oil. [α]2D2 = –113.6 (c = 1.0,
CHCl3). H NMR (400 MHz, CDCl3): δ = 7.58 (d, J = 9.0 Hz, 2
1
H), 7.44–7.30 (m, 10 H), 6.83 (d, J = 9.0 Hz, 2 H), 5.52 (d, J =
1.7 Hz, 1 H), 4.92 (d, J = 10.9 Hz, 1 H), 4.81 (d, J = 11.9 Hz, 1
H), 4.75 (d, J = 11.5 Hz, 1 H), 4.68 (d, J = 10.9 Hz, 1 H), 4.20 (dt,
J = 3.1, 1.5 Hz, 1 H), 4.04 (dd, J = 9.1, 3.4 Hz, 1 H), 3.80 (dq, J
= 9.8, 6.3 Hz, 1 H), 3.55 (t, J = 9.4 Hz, 1 H), 2.73 (d, J = 1.5 Hz,
1 H), 1.29 (d, J = 6.2 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3):
δ = 155.9 (s), 138.3 (d), 138.1 (s), 137.7 (s), 128.6 (d), 128.4 (d),
128.0 (d), 127.9 (d), 127.82 (d), 127.76 (d), 118.5 (d), 97.0 (d), 84.7
(s), 79.67 (d), 79.64 (d), 75.4 (t), 72.3 (t), 68.29 (d), 68.22 (d), 17.9
(q) ppm. HRMS (ESI+): calcd. for C26H27IO5Na [M + Na]+
569.0795; found 569.0807.
1
28α: H NMR (400 MHz, CDCl3): δ = 8.67 (s, 1 H), 7.40–7.29 (m,
10 H), 6.20 (d, J = 1.9 Hz, 1 H), 5.51 (dd, J = 3.3, 2.0 Hz, 1 H),
4.95 (d, J = 10.8 Hz, 1 H), 4.75 (d, J = 11.2 Hz, 1 H), 4.66 (d, J =
10.8 Hz, 1 H), 4.60 (d, J = 11.2 Hz, 1 H), 4.02 (dd, J = 9.5, 3.4 Hz,
1 H), 3.97 (dq, J = 9.8, 6.3 Hz, 1 H), 3.55 (t, J = 9.6 Hz, 1 H), 2.21
(s, 3 H), 1.38 (d, J = 6.2 Hz, 3 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 170.0 (s), 160.1 (s), 138.1 (s), 137.5 (s), 128.4 (d), 128.4
(d), 128.3 (d), 128.1 (d), 127.89 (d), 127.85 (d), 95.2 (d), 79.3 (d),
77.2 (d), 75.6 (t), 72.0 (t), 70.7 (d), 67.6 (d), 21.0 (q), 18.0 (q) ppm.
28β: 1H NMR (400 MHz, CDCl3): δ = 8.66 (s, 1 H), 7.51–7.18 (m,
10 H), 5.90 (d, J = 2.9 Hz, 2 H), 4.96 (d, J = 10.9 Hz, 1 H), 4.79
(d, J = 11.2 Hz, 1 H), 4.66 (d, J = 10.9 Hz, 1 H), 4.55 (d, J =
11.2 Hz, 1 H), 3.77 (dd, J = 8.7, 3.1 Hz, 1 H), 3.68–3.46 (m, 2 H),
2.22 (s, 3 H), 1.44 (d, J = 5.8 Hz, 3 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 170.23 (s), 160.17 (s), 138.07 (s), 137.35 (s), 128.39 (d),
128.32 (d), 128.07 (d), 127.95 (d), 127.82 (d), 127.75 (d), 95.04 (d),
79.49 (d), 79.01 (d), 75.35 (t), 72.79 (d), 71.49 (t), 66.47 (d), 20.85
(q), 17.79 (q) ppm.
p-Iodophenyl
3,4-Di-O-benzyl-2-O-methyl-α-L-rhamnopyranoside
(3): NaH (55% dispersion in mineral oil, 527 mg, 12.1 mmol) was
added at 0 °C to a solution of 30 (3.30 g, 6.04 mmol) and methyl
iodide (1.50 mL, 24.2 mmol) in DMF (30 mL). The mixture was
stirred at 0 °C until completion (1 h), quenched with a saturated
solution of NH4Cl (20 mL), and diluted with Et2O (300 mL). The
organic layer was washed with NH4Cl (20 mL) and brine (20 mL),
dried (Na2SO4), the solvent removed under reduced pressure, and
the residue purified by flash chromatography to give compound 3
(3.20 g, 5.71 mmol, 95% yield) as a colorless oil. [α]2D2 = –101.2 (c
= 1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 7.57 (d, J =
9.0 Hz, 1 H), 7.47–7.29 (m, 10 H), 6.82 (d, J = 9.0 Hz, 2 H), 5.49
(d, J = 1.9 Hz, 1 H), 4.96 (d, J = 10.8 Hz, 1 H), 4.81 (d, J =
12.5 Hz, 1 H), 4.77 (d, J = 12.5 Hz, 1 H), 4.66 (d, J = 10.8 Hz, 1
H), 4.04 (dd, J = 9.3, 3.2 Hz, 1 H), 3.73 (dq, J = 9.8, 6.3 Hz, 1 H),
3.70 (dd, J = 3.2, 2.0 Hz, 1 H), 3.60 (t, J = 9.5 Hz, 1 H), 3.58 (s, 3
H), 1.29 (d, J = 6.2 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3):
δ = 156.1 (s), 138.35 (s), 138.30 (d), 138.26 (s), 128.4 (d), 128.3,
127.9 (d), 127.8 (d), 127.73 (d), 127.66 (d), 118.5 (d), 95.5 (d), 84.7
(s), 80.2 (d), 79.5 (d), 77.8 (d), 75.5 (t), 72.5 (t), 68.8 (d), 59.6 (q),
17.9 (q) ppm. HRMS (ESI+): calcd. for C27H29IO5Na [M + Na]+
583.0952; found 583.0964.
The four compounds interconvert under these conditions and con-
verge into a single product. Similarly, both 28α and 28β can be
used in the next step to give a very similar result.
p-Iodophenyl
2-O-Acetyl-3,4-di-O-benzyl-α-L-rhamnopyranoside
(29): A solution of 28α (4.80 g, 9.04 mmol) in CH2Cl2 (15 mL) was
added to a suspension of 4-iodophenol (3.78 g, 17.2 mmol) in
CH2Cl2 (40 mL) at –45 °C. Then TMSOTf (163 μL, 0.9 mmol) was
added and the mixture stirred while slowly warming to 20 °C.
When 28α had been completely consumed (1.5 h), pyridine (1 mL)
was added to quench the reaction. The mixture was filtered and
the solvents removed under reduced pressure. The residue was di-
luted in EtOAc (300 mL) and washed with a 3 m NaOH solution
(2ϫ 30 mL), water (20 mL), NH4Cl (20 mL), and brine (20 mL).
The organic layer was dried with Na2SO4, the solvent removed un-
der reduced pressure, and the residue purified by flash chromatog-
raphy to give compound 29 (4.79 g, 90% yield) as a colorless oil.
4-[(17R,19R,24S,25R)-17,19-Dihydroxy-25-methoxy-24-methylhep-
tacos-1-ynyl]phenyl 3,4-Di-O-benzyl-2-O-methyl-α-L-rhamnopyrano-
side (31): A stock solution of the catalyst was prepared by mixing
PPh3 (7.0 mg, 26.8 μmol), CuI (10.2 mg, 53.6 μmol), and
[PdCl2(PPh3)2] (18.8 mg, 26.8 μmol) in freshly distilled Et3N
(8.9 mL) and stirring this solution at 40 °C for 15 min. Then this
stock solution (1.8 mL, equivalent loading of 5 mol-% Pd, 5 mol-
% PPh3, and 10 mol-% Cu) was added to a solution of compound
5 (58.2 mg, 128 μmol) and monosaccharide 3 (60.0 mg, 107 μmol)
in freshly distilled Et3N (0.3 mL). The mixture was then stirred at
40 °C until completion (5 h). Triethylamine was removed under a
stream of nitrogen and the residue dissolved in toluene and purified
by column chromatography to give compound 31 (86.0 mg,
97 μmol, 91% yield) as a waxy solid. [α]2D2 = –67.5 (c = 0.5, CHCl3).
1H NMR (400 MHz, CDCl3): δ = 7.42 (d, J = 6.6 Hz, 2 H), 7.38–
7.27 (m, 10 H), 6.93 (d, J = 8.9 Hz, 2 H), 5.51 (d, J = 1.8 Hz, 1
H), 4.95 (d, J = 10.8 Hz, 1 H), 4.81 (d, J = 12.2 Hz, 1 H), 4.75 (d,
J = 12.5 Hz, 1 H), 4.64 (d, J = 10.8 Hz, 1 H), 4.04 (dd, J = 9.3,
3.2 Hz, 1 H), 3.93 (br. s, 2 H), 3.73 (dq, J = 9.8, 6.5 Hz, 1 H), 3.68
(dd, J = 3.2, 2.0 Hz, 1 H), 3.58 (d, J = 9.4 Hz, 1 H), 3.56 (s, 3 H),
3.34 (s, 3 H), 2.87 (ddd, J = 7.5, 5.2, 4.0 Hz, 1 H), 2.37 (t, J =
7.1 Hz, 2 H), 2.34 (s, 2 H), 1.72–1.02 (m, 39 H), 0.92 (t, J = 7.4 Hz,
3 H), 0.84 (d, J = 6.8 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3):
δ = 155.5 (s), 138.43 (s), 138.33 (s), 132.8 (d), 128.4 (d), 128.4 (d),
128.0 (d), 127.9 (d), 127.8 (d), 127.7 (d), 117.8 (s), 116.1 (d), 95.3
(d), 89.4 (s), 86.7 (d), 80.3 (d), 80.0 (s), 79.5 (d), 77.9 (d), 75.5 (t),
72.5 (t), 69.50 (d), 69.45 (d), 68.8 (d), 59.6 (q), 57.4 (q), 42.3 (t),
1
[α]2D2 = –49.6 (c = 1.0, CHCl3). H NMR (300 MHz, CDCl3): δ =
7.58 (d, J = 8.7 Hz, 2 H), 7.42–7.29 (m, 10 H), 6.81 (d, J = 8.7 Hz,
2 H), 5.53 (m, 1 H), 5.44 (s, 1 H), 4.96 (d, J = 10.8 Hz, 1 H), 4.78
(d, J = 11.2 Hz, 1 H), 4.65 (d, J = 10.6 Hz, 1 H), 4.63 (d, J =
11.1 Hz, 1 H), 4.13 (dd, J = 9.3, 3.3 Hz, 1 H), 3.82 (dq, J = 9.8,
6.3 Hz, 1 H), 3.53 (t, J = 9.4 Hz, 1 H), 2.20 (s, 3 H), 1.31 (d, J =
6.2 Hz, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.3 (s), 155.7
(s), 138.4 (d), 138.2 (s), 137.8 (s), 128.4 (d), 128.4 (d), 128.0 (d),
127.9 (d), 127.8 (d), 127.7 (d), 118.6 (d), 95.8 (d), 85.1 (s), 79.8 (d),
77.6 (d), 75.5 (t), 72.0 (t), 68.66 (d), 68.67 (d) 21.0 (q), 17.94
(q) ppm. HRMS (ESI+): calcd. for C28H28IO6Na [M + Na]+
611.0910; found 611.0914.
p-Iodophenyl 3,4-Di-O-benzyl-α-L-rhamnopyranoside (30): Sodium
methoxide (188 mg, 3.48 mmol) was added to a solution of com-
pound 29 (4.1 g, 6.97 mmol) in MeOH (40 mL) and the mixture
was stirred at room temp. until completion (24 h). The resulting
solution was diluted with EtOAc (200 mL) and washed with water
(20 mL) and brine (20 mL). The organic layer was dried (Na2SO4),
the solvent removed under reduced pressure, and the residue puri-
Eur. J. Org. Chem. 2013, 4642–4654
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4651

A. J. Minnaard et al.
37.5 (t), 34.8 (d), 32.6 (t), 29.69 (t), 29.65 (t), 29.63 (t), 29.61 (t), droxybenzoate (1.83 g, 12.04 mmol) were dissolved in CH2Cl2
FULL PAPER
29.60 (t), 29.54 (t), 29.17 (t), 28.93 (t), 28.83 (t), 27.6 (t), 26.1 (t),
25.8 (t), 22.4 (t), 19.4 (t), 17.9 (q), 14.8 (q), 10.1 (q) ppm. HRMS
(ESI+): calcd. for C56H84O8Na [M + Na]+ 907.6064; found
907.6068.
(30 mL). The solution was cooled to 0 °C and BF3·OEt2 (2.3 mL,
18.1 mmol) was added. The reaction was allowed to warm to room
temp. and stirred for 18 h. The reaction was subsequently quenched
with a saturated solution of NaHCO3 (30 mL) and diluted with
EtOAc (200 mL). The organic layer was washed with a saturated
solution of NaHCO3 (30 mL) and brine (30 mL), dried (Na2SO4),
and the solvent removed under reduced pressure. The crude was
purified by flash chromatography to give compound 33 (1.83 g,
4.31 mmol, 72% yield) as a white solid containing less than 4% of
the β anomer, m.p. 115.1–115.7 °C. [α]2D2 = –91.8 (c = 1.0, CHCl3).
1H NMR (400 MHz, CDCl3): δ = 7.98 (d, J = 8.9 Hz, 2 H), 7.09
(d, J = 8.9 Hz, 2 H), 5.52 (d, J = 1.4 Hz, 1 H), 5.48 (dd, J = 10.1,
3.5 Hz, 1 H), 5.42 (dd, J = 3.4, 1.8 Hz, 1 H), 5.14 (t, J = 10.0 Hz,
1 H), 3.92 (dq, J = 8.7, 5.6 Hz, 1 H), 3.87 (s, 3 H), 2.18 (s, 3 H),
2.04 (s, 3 H), 2.02 (s, 3 H), 1.18 (d, J = 6.3 Hz, 3 H) ppm. 13C
NMR (101 MHz, CDCl3): δ = 169.94 (s), 169.93 (s), 169.85 (s),
166.5 (s), 159.2 (s), 131.6 (d), 124.5 (s), 115.8 (d), 95.3 (d), 70.7 (d),
69.4 (d), 68.7 (d), 67.4 (d), 51.9 (q), 20.8 (q), 20.71 (q), 20.67 (q),
17.4 (q) ppm. HRMS (ESI+): calcd. for C20H24O10Na [M + Na]+
447.1262; found 447.1260.
4-[(17R,19R,24S,25R)-17,19-dimycocerosoyloxy-25-methoxy-24-
methylheptacos-1-ynyl]phenyl 3,4-Di-O-benzyl-2-O-methyl-α-L-
rhamnopyranoside (32): A mixture of diol 31 (6.4 mg, 7.1 μmol),
mycocerosic acid (4; 13.8 mg, 29 μmol), EDC hydrochloride
(5.5 mg, 29 μmol), and DMAP (7.0 mg, 57 μmol) were dissolved
in CDCl3 (0.6 mL) and the mixture was stirred overnight. After
completion of the reaction, as determined by 1H NMR of the
crude, the reaction was quenched by adding HCl (1 m in Et2O solu-
tion, 0.2 mL), diluted with toluene, and the solvents partially re-
moved under a nitrogen stream. The crude was purified by flash
chromatography (pentane/Et2O from 2:1 to 1:1) to give compound
32 (8.0 mg, 4.4 μmol, 62% yield). [α]2D2 = –35.0 (c = 0.4, CHCl3).
1H NMR (400 MHz, CDCl3): δ = 7.42 (d, J = 6.6 Hz, 2 H), 7.38–
7.27 (m, 10 H), 6.93 (d, J = 8.7 Hz, 2 H), 5.51 (d, J = 1.8 Hz, 1
H), 4.95 (d, J = 10.8 Hz, 1 H), 4.84 (s, 2 H), 4.78 (s, 2 H), 4.64 (d,
J = 10.8 Hz, 1 H), 4.04 (dd, J = 9.3, 3.1 Hz, 1 H), 3.78–3.65 (m, 2
H), 3.59 (t, J = 9.5, 8.2 Hz, 1 H), 3.56 (s, 3 H), 3.33 (s, 3 H), 2.86
(dt, J = 9.0, 4.6 Hz, 1 H), 2.65–2.43 (m, 2 H), 2.37 (t, J = 7.1 Hz,
2 H), 1.79–0.97 (m, 133 H), 0.96–0.77 (m, 39 H) ppm. 13C NMR
(101 MHz, CDCl3): δ = 176.04 (s), 175.97 (s), 155.5 (s), 138.4 (s),
138.3 (s), 132.8 (d), 128.42 (d), 128.36 (d), 128.0 (d), 127.9 (d),
127.74 (d), 127.66 (d), 117.9 (s), 116.1 (d), 95.4 (d), 89.3 (s), 86.7
(d), 80.3 (d), 80.0 (s), 79. 6 (d), 78.0 (d), 75.5 (t), 72.5 (t), 70.3 (d),
68.8 (d), 59.6 (q), 57.4 (q), 45.3 (t), 41.0 (t), 37.7 (d), 36.6 (t), 34.8
(t), 31.9 (t), 30.3 (d), 30.1 (t), 29.9 (d), 29.7 (t), 29.36 (t), 29.36 (t)
28.99 (t) 28.88 (t), 28.1 (d), 27.5 (t), 27.2 (d), 27.0 (t), 25.6 (t), 25.2
(t), 22.7 (t), 22.3 (t), 20.8 (q), 20.5 (q), 20.41 (q), 20.38 (q), 19.4 (t),
18.4 (q), 17.9 (q), 14.1 (q), 10.1 (q) ppm. HRMS (ESI+): calcd. for
4-(Methoxycarbonyl)phenyl α-L-Rhamnose (34): Sodium methoxide
(17 mg, 0.32 mmol) was added to a solution of compound 33
(1.37 g, 3.23 mmol) in MeOH (10 mL) and the mixture was stirred
at room temp. until complete conversion was observed by TLC
(2 h). The reaction was quenched by the addition of Amberlite H+
(10 g) and the mixture stirred for 5 min. The mixture was filtered,
the solvent removed under reduced pressure, and the crude was
purified by flash chromatography to give compound 34 (903 mg,
3.03 mmol, 94% yield) as a white solid, m.p. 44–46 °C. [α]2D2
=
–119.4 (c = 1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 7.97 (d,
J = 9.0 Hz, 2 H), 7.06 (d, J = 9.0 Hz, 2 H), 5.59 (d, J = 1.5 Hz, 1
H), 4.18 (br. s, 1 H), 4.01 (dt, J = 8.3, 4.0 Hz, 1 H), 3.89 (s, 3 H),
3.71 (dq, J = 10.2, 6.1 Hz, 1 H), 3.60 (td, J = 9.5, 2.2 Hz, 1 H),
3.46 (d, J = 5.0 Hz, 1 H), 3.28 (d, J = 3.6 Hz, 1 H), 3.05 (br. s, 1
H), 1.27 (d, J = 6.1 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3):
δ = 166.7 (s), 159.5 (s), 131.5 (d), 124.0 (s), 115.6 (d), 97.4 (d), 72.7
(d), 71.4 (d), 70.7 (d), 69.2 (d), 52.0 (q), 17.5 (q) ppm. HRMS
(ESI+): calcd. for C14H18O7Na [M + Na]+ 321.0945; found
321.0944.
C
120H208O10Na [M + Na]+ 1833.5693; found 1833.5673.
Mycoside B (1): Palladium on carbon (10% dry basis Degussa type
E101 NE/W, 9.4 mg of wet compound, 1 equiv.) was added to a
solution of diester 32 (8.0 mg, 4.4 μmol) in a mixute of EtOAc
(0.8 mL) and EtOH (0.2 mL) under nitrogen. A balloon filled with
H2 was attached to the apparatus and the reaction was stirred for
4 h. Then the catalyst was removed by filtration through a plug of
cotton and Celite, eluting with additional EtOAc (20 mL). The sol-
vent was removed under reduced pressure and the crude was puri-
fied by flash chromatography to give mycoside B (1; 5.5 mg,
3.4 μmol, 76% yield) as a waxy solid. The spectroscopic data coin-
cide with that reported for the natural product.[6] [α]2D2 = –19.5 (c
= 0.275, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 7.10 (d, J =
8.4 Hz, 2 H), 6.98 (d, J = 8.5 Hz, 2 H), 5.54 (s, 1 H), 4.84 (t, J =
6.1 Hz, 2 H), 3.92 (dd, J = 9.5, 2.8 Hz, 1 H), 3.75 (dq, J = 10.5,
6.2 Hz, 1 H), 3.66 (d, J = 2.4 Hz, 1 H), 3.52 (s, 3 H), 3.44 (t, J =
9.5 Hz, 3 H), 3.33 (s, 3 H), 2.85 (d, J = 4.9 Hz, 1 H), 2.55 (d, J =
7.6 Hz, 2 H), 1.98–0.79 (m, 176 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 175.99 (s), 175.96 (s), 154.48 (s), 136.88 (s), 129.32 (d),
116.12 (d), 94.73 (d), 86.65 (d), 80.16 (d), 74.00 (d), 71.41 (d), 70.29
(d), 68.36 (d), 58.97 (q), 57.37 (q), 45.51 (t), 45.30 (t), 40.98 (t),
38.45 (t), 37.78 (d), 37.74 (d), 36.63 (t), 35.13 (t), 34.81 (t), 34.70
(d), 32.62 (t), 31.93 (t), 31.69 (t), 30.09 (t), 29.94 (d), 29.79 (t), 29.72
(t), 29.66 (t), 29.58 (t), 29.55 (t), 29.36 (t), 29.34 (t), 28.05 (d), 27.49
(t), 27.21 (d), 26.97 (t), 25.56 (t), 25.16 (t), 22.69 (t), 22.35 (t), 20.76
(q), 20.46 (q), 20.42 (q), 20.39 (q), 18.43 (q), 17.56 (q), 14.72 (q),
14.12 (q), 10.10 (q) ppm. HRMS (ESI+): calcd. for C106H200O10Na
[M + Na]+ 1657.5067; found 1657.5058.
4-(Methoxycarbonyl)phenyl 3,4-O-Ley-protected-2-O-Methyl-α-L-
rhamnose (also Methyl 4-{[(2R,3R,4aS,5S,7S,8R,8aR)-2,3,8-Tri-
methoxy-2,3,5-trimethylhexahydro-2H-pyrano[3,4-b][1,4]dioxin-7-
yl]oxy}benzoate, 35): Amberlite-H+ 1200 (6.5 g) was added to a
solution of 2,3-butadione (11.7 g, 136 mmol) and trimethyl ortho-
formate (60 mL, 544 mmol) in methanol (225 mL). The mixture
was heated at reflux for 2 d (GC analysis shows, though, little dif-
ference between 24 and 48 h) and then filtered. The volatiles were
removed under reduced pressure in a rotavap to give a dark crude
oil. 1H and 13C NMR analysis of this oil showed 2,2,3,3-tetrameth-
oxybutane as the product. (GC–MS analysis also showed a peak
corresponding to 2,3,3-trimethoxy-1-butene, but this is probably
due to partial elimination of methanol in the injector). The crude
oil was used in the next step without further purification.
BF3·OEt2 (5.1 μL, 40 μmol) was added at 0 °C to a solution of
monosaccharide 34 (400 mg, 1.34 mmol) and crude 2,2,3,3-tetra-
methoxybutane (311 mg, 1.74 mmol) in acetonitrile (4 mL). The re-
action was stirred until TLC analysis showed complete consump-
tion of 34 (2.5 h). Then iodomethane (335 μL, 5.36 mmol) and
NaH (60% in mineral oil, 215 mg, 5.36 mmol) were added to the
reaction, which was stirred until complete conversion of the inter-
mediate alcohol (1 h). The reaction was diluted with EtOAc
4-(Methoxycarbonyl)phenyl 2,3,4-Tri-O-acetyl-α-
L-rhamnose (33):
Peracetylated rhamnose 23 (2.00 g, 6.02 mmol) and methyl p-hy-
4652
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 4642–4654

Total Synthesis of Mycoside B and HBAD-I
K. C. Onwueme, C. J. Vos, J. Zurita, J. A. Ferreras, L. E. N.
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Ginsburg, E. Lederer, Biochim. Biophys. Acta 1963, 70, 442–
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(70 mL) and washed with water (15 mL) and brine (15 mL). The
organic phase was dried (Na2SO4) and the solvent removed under
reduced pressure. The crude was purified by flash chromatography
to give compound 35 (246 mg, 0.58 mmol, 43% yield) as a white
solid containing 10% of a minor diastereomer (in the dioxolanone
[5]
[6]
[7]
1
ring), m.p. 176–178 °C. [α]2D2 = –254.2 (c = 1.0, CHCl3). H NMR
(400 MHz, CDCl3): δ = 7.98 (d, J = 9.0 Hz, 2 H), 7.06 (d, J =
8.9 Hz, 2 H), 5.60 (d, J = 1.6 Hz, 1 H), 4.20–4.15 (m, 1 H), 3.87
(s, 3 H), 3.83–3.72 (m, 2 H), 3.65 (dd, J = 3.1, 1.7 Hz, 1 H), 3.56
(s, 3 H), 3.34 (s, 3 H), 3.25 (s, 3 H), 1.35 (s, 3 H), 1.28 (s, 3 H),
1.21 (d, J = 5.7 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3): δ =
166.67 (s), 159.8 (s), 131.5 (d), 123.9 (s), 115.7 (d), 100.0 (s), 99.6
(s), 95.7 (d), 78.3 (d), 68.35 (d), 68.05 (d), 68.00 (d), 59.4 (q), 51.9
(q), 48.00 (q), 47.6 (q), 17.77 (q), 17.76 (q), 16.6 (q) ppm. HRMS
(ESI+): calcd. for C21H30O9Na [M + Na]+ 449.1782; found
449.1783.
[8]
[9]
4-(Methoxycarbonyl)phenyl 2-O-Methyl-α-L-rhamnose (p-HBAD-I,
2): Compound 35 (240 mg, 0.56 mmol) was dissolved in TFA/water
(9:1) at room temp. and after 2 min the volatiles were evaporated
under reduced pressure. The crude was purified by flash
chromatography to give compound 2 (87 mg, 0.28 mmol, 50%
yield) as a white solid. The spectroscopic data coincide with that
reported for the natural product, m.p. 113–114 °C. [α]2D2 = –94.6 (c
= 1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 8.00 (d, J =
7.4 Hz, 3 H), 7.10 (d, J = 7.4 Hz, 2 H), 5.65 (s, 1 H), 3.98–3.89 (m,
1 H), 3.89 (s, 3 H), 3.67 (dd, J = 14.4, 5.0 Hz, 2 H), 3.54 (s, 3 H),
3.46 (t, J = 9.1 Hz, 1 H), 2.58 (s, 2 H), 1.26 (d, J = 5.3 Hz, 3
H) ppm. 13C NMR (101 MHz, CDCl3): δ = 166.6 (s), 159.8 (s),
131.5 (d), 123.9 (s), 115.7 (d), 94.4 (d), 80.0 (d), 73.1 (d), 71.1 (d),
69.0 (d), 59.1 (q), 51.87 (q), 17.5 (q) ppm. HRMS (ESI+): calcd.
for C15H20O7Na [M + Na]+ 335.1101; found 335.1107.
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Received: March 24, 2013
Published Online: June 12, 2013
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