Synthesis and reactions of fluorous carbobenzyloxy (fCbz) derivatives of α-amino acids

Article abstract of DOI:10.1021/jo0344283

Fluorous carbobenzyloxy (^FCbz) reagents RfCH₂CH₂C₆H₄CH₂ OC(O)OSu (where Su is succinimidoyl and Rf is C₆F₁₃ and C₈F₁₇) have been used to make

Full text of DOI:10.1021/jo0344283

Syn th esis a n d Rea ction s of F lu or ou s Ca r boben zyloxy (F Cbz)
Der iva tives of r-Am in o Acid s
Dennis P. Curran,*,1a Muriel Amatore,1a David Guthrie,1a Matthew Campbell,1a
Eisan Go,1a and Zhiyong Luo1b
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, and
Fluorous Technologies, Inc., 970 William Pitt Way, Pittsburgh, Pennsylvania 15238
curran@pitt.edu
Received April 3, 2003
Fluorous carbobenzyloxy (FCbz) reagents RfCH2CH2C6H4CH2OC(O)OSu (where Su is succinimidoyl
F
and Rf is C6F13 and C8F17) have been used to make Cbz derivatives of 18 of the 20 natural amino
acids. The potential utility of this new family of reagents in both standard fluorous synthesis with
spe separation and fluorous quasiracemic synthesis is illustrated with representative reactions of
the FCbz-Phe derivatives.
In tr od u ction
fluorous Cbz reagents.8 They used these reagents for
tagging and purification in solid-phase synthesis of small
peptides. We describe herein the synthesis of two families
of FCbz-tagged R-amino acids, and we validate the utility
of representative family members in both standard
fluorous synthesis and fluorous mixture synthesis ap-
plications.
Fluorous tagging methods for small molecule synthesis
appeal because they couple the breadth of solution-phase
reaction chemistry with convenient yet effective methods
of separation.2 In standard fluorous synthesis methods,
solid-phase extraction over fluorous silica gel quickly
bifurcates mixtures into fluorous-tagged and untagged
fractions.3 In fluorous mixture synthesis, fluorous chro-
matography is used to separate fluorous-tagged molecules
from each other based on the tag.4 The applicability of
these methods is directly proportional to the availability
of fluorous tags.
Resu lts a n d Discu ssion
Fluorous CbzOSu reagents 1a and 1b with the N-
hydroxysuccinimide group were readily prepared as
shown in eq 1. Reduction of the appropriate methyl ester9
Fluorous tags are often fashioned after standard
protecting groups for organic functionalities by addition
of one or more fluoroalkyl substituents. A small assort-
ment of fluorous oxygen protecting groups is known,2,4,5
and fluorous Boc (FBoc) groups show good potential for
nitrogen protection.6 Carbobenzyloxy (Cbz) groups are
popular for nitrogen protection,7 and very recently van
Boom and co-workers reported the synthesis of several
(1) (a) University of Pittsburgh; M.A., D.G., M.C., and E.G. are
undergraduate researchers from l’Universite´ Pierre et Marie Curie,
St. Vincent College, University of Pittsburgh, and Osaka University.
(b) Fluorous Technologies, Inc. (FTI).
(2) (a) Studer, A.; Hadida, S.; Ferritto, R.; Kim, S. Y.; J eger, P.; Wipf,
P.; Curran, D. P. Science 1997, 275, 823-826. (b) Curran, D. P. Angew.
Chem., Int. Ed. Engl. 1998, 37, 1175-1196. (c) Curran, D. P. In
Stimulating Concepts in Chemistry; Vo¨gtle, F., Stoddard, J . F.,
Shibasaki, M., Eds.; Wiley-VCH: New York, 2000.
(Rf ) C8F17 or C6F13) with LAH followed by exposure of
the resulting alcohol to phosgene and N-hydroxysuccin-
imide (NHS) gave 1a ,b. These reagents are now com-
mercially available from Fluorous Technologies, Inc.9
FCbz reagents 1a ,b are white solids that are trans-
ferred in the open atmosphere by standard techniques,
and their reactions with amines and amino acids are
straightforward. The tagging of (L)-phenylalanine with
larger FCbz reagent 1a is typical (Figure 1).
(3) (a) Curran, D. P.; Luo, Z. Y. J . Am. Chem. Soc. 1999, 121, 9069-
9072. (b) Curran, D. P. Synlett 2001, 1488-1496.
(4) (a) Luo, Z. Y.; Zhang, Q. S.; Oderaotoshi, Y.; Curran, D. P. Science
2001, 291, 1766-1769. (b) Curran, D. P.; Oderaotoshi, Y. Tetrahedron
2001, 57, 5243-5253. (c) Zhang, W.; Chen, C. H.-T.; Luo, Z.; Curran,
D. P. J . Am. Chem. Soc. 2002, 124, 10443-10450. (d) Zhang, Q. S.;
Rivkin, A.; Curran, D. P. J . Am. Chem. Soc. 2002, 124, 5774-5781.
(5) (a) Wipf, P.; Reeves, J . T. Tetrahedron Lett. 1999, 40, 4649-
4652. (b) Rover, S.; Wipf, P. Tetrahedron Lett. 1999, 40, 5667-5670.
(c) Wipf, P.; Reeves, J . T. Tetrahedron Lett. 1999, 40, 5139-5142.
(6) Luo, Z. Y.; Williams, J .; Read, R. W.; Curran, D. P. J . Org. Chem.
2001, 66, 4261-4266.
A solution of 1a (1.44 mmol) in THF (30 mL) was added
to (L)-phenylalanine (2.1 mmol) and triethylamine (2.1
mmol) in water (5 mL). After 1 h, the mixture was
(8) Filippov, D. V.; van Zoelen, D. J .; Oldfield, S. P.; van der Marel,
G. A.; Overkleeft, H. S.; Drijfhoutb, J . W.; van Boom, J . H. Tetrahedron
Lett. 2002, 43, 7809-7812.
(9) www.fluorous.com. DPC is the Founder of FTI and holds an
equity stake in the company.
(7) Green, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.; Wiley: New York, 1999; pp 531-537. CBz groups
are also called benzyl carbamates and often abbreviated as Z.
10.1021/jo0344283 CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/20/2003
J . Org. Chem. 2003, 68, 4643-4647
4643

Curran et al.
TABLE 1. P r ep a r a tion of F CBz-Ta gged Am in o Acid sa
entry
amino acid
FCbz rgt
yieldb
1
2
3
4
5
6
7
8
9
Gly
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
88 (46)
81 (58)
89 (46)
84 (52)
89 (66)
100 (69)
97
(L)-Ala
(L)-Val
(L)-Leu
(L)-Ile
(L)-Ser
(L)-Phe
(L)-Asn
(L)-Gln
(L)-Thr
(L)-Met
(L)-Asp
(L)-Gle
(L)-Trp
(L)-Tyr
(L)-Proc
Gly
92
97
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
82 (65)
84 (70)
61 (38)
92 (39)
83 (67)
92 (69)
87
95
92
95
85
89
80 (69)
95
92
97
88 (72)
95
97
85 (83)
72 (64)
92 (66)
81
(D)-Ala
(D)-Val
(D)-Leu
(D)-Ile
(D)-Ser
(D)-Phe
(D)-Asn
(D)-Gln
(D)-Thr
(D)-Met
(D)-Asp
(D)-Gle
(D)-Trp
(D)-Tyr
(D)-Proc
F IGURE 1. FCbz reagents and tagged phenylalanine quasi-
enantiomers.
a
b
Et3N, THF/H2O, 25 °C, 2-24 h. Crude yield (recrystallized
yield). c NaHCO3 was used as base.
acidified to pH 2 with HCl and extracted with ethyl
acetate. The ethyl acetate phase was washed, dried, and
evaporated to provide substantially pure FCbz-(L)-Phe 2a
in 97% yield. The product could be further purified by
recrystallization from acetonitrile, if desired. Similarly,
(D)-phenylalanine was tagged with the smaller Cbz
reagent 1b to give FCbz-(D)-Phe 2b in 95% yield.
Sixteen of the twenty common amino acids were tagged
in similar reactions, and the results of this series of
experiments are summarized in Table 1.
In preparation for a mixture or quasiracemic synthesis
applications, all the natural (L)-amino acids were given
the larger C8F17 tag, while the unnatural (D)-amino acids
got the smaller C6F13 tag. Achiral glycine was tagged with
both reagents. Scales ranged from several hundred
milligrams to several grams. All 32 of the products were
isolated as white solids in good to excellent yield. Further
purification by recrystallization was conducted for a little
over half of the products. The remainder were deemed
sufficiently pure to be used in crude form, although they
could almost certainly be recrystallized if desired.
needed to generate FCbz analogues of these functionalized
amino acids.
Several reactions of the phenylalanine derivatives (L)-
2a and (D)-2b were undertaken to show the utility of the
FCbz-tagged amino acids and to validate separations over
fluorous silica gel. Coupling reactions of 2a ,b were
conducted with four different amines under standard
conditions (EDCI, HOBt) as shown in Table 2. The
amines were used in excess (4 equiv) and the excess
amine and other reagents were removed by rapid solid-
phase extraction3b of the crude reaction products through
FluoroFlash silica gel cartridges.9 The crude coupled
products were isolated in moderate to excellent yields in
very good states of purity (see Supporting Information
1
for H NMR spectra). Although the spe’s with the C6F13
derivatives succeeded, the retention times of these prod-
ucts on fluorous silica are moderate (see below), so we
recommend C8F17 derivatives as first choices for standard
fluorous synthesis applications.
Two different protected forms of cysteine were gener-
ated, as shown in Figure 2. Reaction of (L)-cystine with
1a and (D)-cystine with 1b gave the corresponding
dimeric FCbz derivatives, while reactions of (L)-S-benzyl
cysteine ((L)-CysSBn) with 1a ,b gave the corresponding
FCbz-SBn derivative. Once again, all derivatives were
white solids. The enantiomers of (ꢀ)-Boc-Lys were also
tagged in the standard fashion to give the corresponding
(ꢀ)-Boc-FCbz-Lys analogues in good yields. Finally, pre-
liminary attempts to make FCbz derivatives from free
arginine and histidine did not succeed, so either modified
procedures or suitably protected amino acids will be
The tagging of the (L)- and (D)-amino acids with
different tags sets the stage for the formation and
reactions of amino acid quasiracemates.4a,d To demon-
strate the potential, an FCbz-Phe quasiracemate was
made by mixing equal portions of (L)-2a and (D)-2b to
give M-2a ,b (where the prefix “M” stands for “mixture”).
Quasiracemate M-2a ,b was then reacted with tetra-
hydroisoquinoline under standard coupling conditions
(see Figure 3), and the crude product was both purified
and demixed (resolved into its quasienantiomeric com-
ponents) by HPLC with a preparative FluoroFlash col-
umn.9 Elution was conducted with a linear gradient of
4644 J . Org. Chem., Vol. 68, No. 12, 2003

Fluorous CBz Amino Acids
F IGURE 3. Reactions of phenylalanine quasienantiomers.
elutes with the solvent front under these conditions).
Pure quasienantiomer (D)-3b eluted after 10.2 min (83%)
and pure quasienantiomer (L)-3a eluted after 16.0 min
(81%).
F IGURE 2. FCbz derivatives of cysteine and lysine.
TABLE 2. Rea ction s of F CBz-Ta gged P h en yla la n in es
The large differences in retention time suggested that
the crude product could also be purified and demixed by
flash chromatography. The reaction was repeated and
this time the product was separated by rapid manual
(“flash”) chromatography over a FluoroFlash cartridge
(instead of an HPLC column). Fractions from elution with
80% MeOH/water containing reagents and excess amine
were discarded. Fractions from elution with 90% MeOH/
water yielded pure quasienantiomer (D)-3b (76%). Eluting
with absolute MeOH gave pure quasienantiomer (L)-3a
(66%).
Finally, we briefly investigated the cleavage of the
FCbz group by hydrogenation. Adduct 3b was stirred in
MeOH with Pd-C under a hydrogen atmosphere for 5
h. After filtration and flash chromatography, we isolated
83% yield of the corresponding free amine (not shown)
alongside 75% of the fluorous toluene C6F13CH2CH2C6H4-
p-CH3. This suggests that FCbz removal under conditions
used for standard Cbz groups will be possible.
Con clu sion s
We suggest that the FCbz amino acids described in this
Article and related compounds will be useful reagents
in medicinal chemistry, peptide chemistry, and other
areas. In traditional applications, the individual reagents
function like standard Cbz-protected amino acids with
F
the advantage that the Cbz-tagged products can readily
80% acetonitrile water up to 100% acetonitrile over 30
min. Excess amine and coupling reagents eluted with the
solvent front at about 2 min (for reference, the standard
Cbz-tagged product lacking a fluoroalkyl group also
be separated from nonfluorous products by either fluo-
rous spe or chromatography. We currently recommend
the longer C8F17 tag for spe separations, but either tag
is useful for chromatographic separations.
J . Org. Chem, Vol. 68, No. 12, 2003 4645

Curran et al.
was stirred at room temperature for 1 h. After the reaction
was complete, the mixture was acidified with aqueous HCl to
pH ∼2 and diluted with ethyl acetate (60 mL). The organic
layer was extracted with water three times and dried with
magnesium sulfate. After drying, magnesium sulfate was
filtered off. The filtrate was evaporated and the residue was
recrystallized from acetonitrile to give a solid, which was
washed with distilled hexane to give product (0.722 g, 67%)
as a white solid: 1H NMR (CDCl3) δ 7.29-7.07 (m, 9H), 5.14
(d, J ) 7.89 Hz, 1H), 5.07 (s, 2H), 4.69 (dd, J ) 13.2, 6.05 Hz,
1H), 3.21 (dd, J ) 13.7, 5.35 Hz, 1H), 3.11 (dd, J ) 14.2, 6.39
Hz, 1H), 2.93-2.88 (m, 2H), 2.44-2.26 (m, 2H).
The quasiracemates generated by deliberate mixing
are useful reagents in their own right. For example,
coupling of a library of n nucleophiles with one quasi-
racemate followed by n chromatographic purifications
will give 2n products (the products after detagging are
enantiomers if the nucleophile is achiral and diastereo-
mers if it is chiral). Further efficiency increases can be
extracted if more homologous tags are introduced and
structurally different tagged amino acids are mixed for
use in fluorous mixture synthesis.4 Finally, either the
fluorous tagging reagents 1a ,b or the fluorous amino
acids themselves can be used for tagging and purification
purposes in solid-phase peptide synthesis.8
Gen er a l P r oced u r es for Cou p lin gs in Ta ble 2. Syn -
th esis of [1-Ben zyl-2-(3,4-d ih yd r o-1H-isoqu in olin -2-yl)-
2-oxoet h yl]ca r b a m ic Acid 4-(3,3,4,4,5,5,6,6,7,7,8,8,8-t r i-
d eca flu or ooctyl) Ben zyl Ester (Ta ble 2, en tr y 2). To a
solution of 2b (50 mg, 0.078 mmol), EDCI (22.2 mg, 0.12
mmol), and HOBt (15.7 mg, 0.12 mmol) in chloroform/DMF
(0.65 mL/0.65 mL) was added 1,2,3,4-tetrahydroisoquinoline
(38.8 µL, 0.31 mmol) and triethylamine (16.3 µL, 0.12 mmol).
The mixture was stirred at room temperature for 18 h. After
the reaction, the solvents were evaporated and the product
was purified by fluorous solid-phase extraction (F-SPE). The
crude reaction mixture dissolved in THF (0.7 mL) was loaded
to a 2-g FluoroFlash column purchased from Fluorous Tech-
nologies, Inc. After elution of the organic compounds with 80/
20 MeOH/H2O, the fluorous product was eluted with ether and
evaporation of solvents gave product (38.2 mg, 65%) as a white
oily solid: 1H NMR (CDCl3) δ 7.32-7.03 (m, 12H), 6.87 (d, J
) 6.21 Hz, 1H), 5.78 (br, 1H), 5.07 (s, 2H), 4.98 (dd, J ) 15.5,
7.24 Hz, 1H), 4.65 (dd, J ) 59.5, 17.1 Hz, 1H), 4.21 (dd, J )
155, 16.0 Hz, 1H), 3.85-3.62 (m, 1H), 3.59-3.10 (m, 1H), 3.07-
2.98 (m, 2H), 2.94-2.89 (m, 2H), 2.78-2.68 (m, 2H), 2.45-
2.27 (m, 2H); 19F NMR (CDCl3) δ -79.5 (3F), -113.4 (2F),
-120.7 (2F), -121.6 (2F), -122.3 (2F), -124.9 (2F); 13C NMR
(CDCl3) δ 170.2, 155.7, 139.1-126.1 (m), 118.4-110.8 (m), 66.6,
52.2, 47.1, 44.6, 43.1, 40.3, 32.8, 29.1, 26.2; LRMS m/z (rel
intensity) 437 (100), 132 (87); HRMS calcd for C34H29F13N2O3
760.1970, found 760.2003; IR (KBr) 3292, 1717, 1637, 1455,
Exp er im en ta l Section
Syn t h esis of 4-(1H ,1H ,2H ,2H -P er flu or od ecyl)b en zyl
Alcoh ol. Under N2 atmosphere, LiAlH4 (0.80 g, 20 mmol) was
dissolved in anhydrous ether (50 mL). The mixture was cooled
to 0-5 °C internal temperature (ice-water bath). To this was
added dropwise a solution of methyl benzoate (11.37 g, 20
mmol) in ether (40 mL). The reaction was stirred at 0-5 °C
for 1 h. Water (1 mL) was added dropwise very slowly to
quench the reaction, then 2 N HCl (55 mL) was added and
the mixture was stirred well. The layers were separated and
the aqueous layer was extracted with ether (1 × 50 mL). The
combined ether layers were washed with 1 N HCl (1 × 5 mL)
and brine (1 × 50 mL). The product was dried over MgSO4,
filtered, and concentrated in vacuo to give a yield of 10.61 g
(19.1 mmol, 90%). A similar procedure was used for the lower
homolog.
Syn th esis of Rf8 Cbz-OSu Rea gen t 1b. Phosgene (20%
in toluene, 7.9 mL, 15 mmol) was charged to a flask and cooled
to 0-5 °C (ice water bath). [CAUTION: Phosgene is highly
toxic and must be handled with appropriate precautions.] To
this was added a solution of 4-(1H,1H,2H,2H-perfluorodecyl)-
benzyl alcohol (5.54 g, 10 mmol) in THF (25 mL). The mixture
was stirred at room temperature for 18 h. After evaporation
to dryness, the product was taken up in chloroform (50 mL).
N-Hydroxysuccinimide dicyclohexylamine salt (3.26 g, 11
mmol) was added portionwise over 10 min, and the mixture
was stirred at room temperature for 3 h. The reaction was
quenched with H2O (100 mL). The product was extracted with
chloroform (3 × 100 mL), dried over MgSO4, filtered, and
concentrated in vacuo. The crude product was recrystallized
in toluene (100 mL) to give 5.55 g (80%) of 1b. A similar
procedure was used for the lower homolog.
P r ep a r a t ion of 3-P h en yl-2-[4-(3,3,4,4,5,5,6,6,7,7,8,8,8-
t r i d e c a flu o r o o c t y l)b e n z y lo x y c a r b o n y la m i n o ]p r o -
p ion ic Acid (2b). To a solution of D-phenylalanine (416 mg,
2.52 mmol) and carbonic acid 2,5-dioxopyrrolidin-1-yl ester
4-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyl) benzyl ester 1b
(1 g, 1.68 mmol) in THF/H2O (30 mL/5 mL) was added
triethylamine (354 µL, 2.52 mmol). The mixture was stirred
at room temperature for 1 h. After the reaction was complete,
the mixture was acidified with aqueous HCl to pH ∼2 and
diluted with ethyl acetate (60 mL). The organic layer was
extracted with water three times and dried with magnesium
sulfate. After drying, magnesium sulfate was filtered off and
the filtrate was evaporated to give product (1.06 g, 98%) as a
white solid: 1H NMR (CDCl3) δ 7.30-7.14 (m, 9H), 5.14 (d, J
) 7.97 Hz, 1H), 5.08 (s, 2H), 4.70 (dd, J ) 13.4, 5.98 Hz, 1H),
3.22 (dd, J ) 13.7, 5.35 Hz, 1H), 3.12 (dd, J ) 14.2, 6.39 Hz,
1H), 2.95-2.89 (m, 2H), 2.45-2.27 (m, 2H).
P r ep a r a tion of 3-P h en yl-2-[4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,
10,10,10-h ep ta d eca flu or o-d ecyl)ben zyloxyca r bon yla m i-
n o]p r op ion ic Acid (2a ). To a solution of L-phenylalanine
(356.8 mg, 2.16 mmol) and carbonic acid 2,5-dioxopyrrolidin-
1-yl ester 4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-
decyl) benzyl ester (1 g, 1.44 mmol) in THF/H2O (30 mL/5 mL)
was added triethylamine (300.5 µL, 2.16 mmol). The mixture
1239, 1144 cm-1; [R]25 -0.0803 (c 0.4, CH2Cl2).
D
[1-Ben zyl-2-(3,4-d ih yd r o-1H -isoq u in olin -2-yl)-2-oxo-
eth yl]ca r ba m ic Acid 4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-
Hep ta d eca flu or od ecyl) Ben zyl Ester (Ta ble 2, en tr y 1).
1H NMR (CDCl3) δ 7.32-7.03 (m, 12H), 6.87 (d, J ) 6.30 Hz,
1H), 5.78 (br, 1H), 5.07 (s, 2H), 4.98 (dd, J ) 15.3, 7.11 Hz,
1H), 4.65 (dd, J ) 59.4, 17.1 Hz, 1H), 4.22 (dd, J ) 155, 16.0
Hz, 1H), 3.85-3.62 (m, 1H), 3.59-3.09 (m, 1H), 3.07-2.98 (m,
2H), 2.94-2.89 (m, 2H), 2.78-2.68 (m, 2H), 2.45-2.27 (m, 2H);
19F NMR (CDCl3) δ -79.5 (3F), -113.4 (2F), -120.4 (2F),
-120.6 (4F), -121.4 (2F), -122.2 (2F), -124.8 (2F); 13C NMR
(CDCl3) δ 170.4, 155.7, 139.1-126.1 (m), 118.4-110.8 (m), 66.6,
52.2, 47.1, 44.6, 43.1, 40.3, 32.8, 29.1, 26.2; LRMS m/z (rel
intensity) 537 (74), 427 (69), 187 (100), 132 (85); HRMS calcd
for C36H29F17N2O3 860.1906, found 860.1893; IR (KBr) 3298,
1717, 1641, 1455, 1205, 1148 cm-1; [R]25 +0.05 (c 0.4, CH2-
D
Cl2).
(1-Cycloh exylca r ba m oyl-2-p h en yleth yl)ca r ba m ic Acid
4-(3,3,4,4,5,5,6,6,7,7,8,8,8-Tr id eca flu or ooct yl)
Ben zyl
1
Ester (Ta ble 2, en tr y 4). H NMR (CDCl3) δ 7.32-7.03 (m,
12H), 5.49 (br, 1H), 5.35 (br, 1H), 5.07 (s, 2H), 4.28 (dd, J )
13.8, 7.52 Hz, 1H), 3.72-3.59 (m, 1H), 3.13 (dd, J ) 13.3, 5.70
Hz, 1H), 2.98-2.89 (m, 3H), 2.45-2.27 (m, 2H), 1.79-0.78 (m,
10H); 19F NMR (CDCl3) δ -79.5 (3F), -113.4 (2F), -120.7 (2F),
-121.6 (2F), -122.3 (2F), -124.9 (2F); 13C NMR (CDCl3) δ
169.5, 155.8, 139.3-127.1 (m), 119.1-110.8 (m), 66.7, 56.6,
48.3, 39.3, 32.9, 25.4, 24.7; LRMS m/z (rel intensity) 556 (30),
437 (100), 229 (35), 164 (45); HRMS calcd for C31H31F13N2O3
726.2127, found 726.2094; IR (KBr) 3303, 1692, 1646, 1535,
1244, 1144 cm-1; [R]25 -0.0665 (c 0.4, CH2Cl2); mp 127-129
D
°C.
(1-Cycloh exylca r ba m oyl-2-p h en yleth yl)ca r ba m ic Acid
4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-H e p t a d e ca flu or o-
4646 J . Org. Chem., Vol. 68, No. 12, 2003

Fluorous CBz Amino Acids
1
d ecyl) Ben zyl Ester (Ta ble 2, en tr y 3). H NMR (CDCl3) δ
7.32-7.03 (m, 12H), 5.50 (br, 1H), 5.35 (br, 1H), 5.07 (s, 2H),
4.28 (dd, J ) 13.5, 7.51 Hz, 1H), 3.70-3.60 (m, 1H), 3.14 (dd,
J ) 13.3, 5.57 Hz, 1H), 2.98-2.89 (m, 3H), 2.45-2.27 (m, 2H),
1.79-0.78 (m, 10H); 19F NMR (CDCl3) δ -79.5 (3F), -113.4
(2F), -120.4 (2F), -120.7 (4F), -121.5 (2F), -122.2 (2F),
-124.8 (2F); 13C NMR (CDCl3) δ 169.5, 155.8, 139.3-127.1 (m),
119.1-110.8 (m), 66.7, 56.6, 48.2, 39.3, 32.9, 25.4, 24.7; LRMS
m/z (rel intensity) 656 (8), 537 (60), 230 (35), 164 (22); HRMS
calcd for C33H31F17N2O3 826.2063, found 826.2088; IR (KBr)
Rea ction of th e M-2a ,b w ith 1,2,3,4-Tetr a h yd r oiso-
qu in olin e a n d Sep a r a tion of 3b a n d 4a fr om th e Rea c-
tion Mixtu r e by F -SP E (F igu r e 3). To a solution of 2a (50
mg, 0.078 mmol), 2b (57.7 mg, 0.078 mmol), EDCI (44.4 mg,
0.23 mmol), and HOBt (31.4 mg, 0.23 mmol) in chloroform/
DMF (1.3 mL/1.3 mL) was added 1,2,3,4-tetrahydroisoquino-
line (77.6 µL, 0.62 mmol) and triethylamine (32.6 µL, 0.23
mmol). The mixture was stirred at room temperature for 18
h. The solvents were evaporated and the product was extracted
by fluorous solid-phase extraction (F-SPE). The crude reaction
mixture dissolved in THF (0.7 mL) was loaded to a 20-g
FluoroFlash column purchased from Fluorous Technologies,
Inc. After elution of the organic compounds with 80/20 MeOH/
H2O, compound 3b was eluted with 90/10 MeOH/H2O and
compound 3a was eluted with 100% MeOH. After purification
by regular silica gel column, 3b (44.8 mg, 76%) and 3a (44.2
mg, 66%) were obtained as white oily solids, which were
3301, 1693, 1647, 1536, 1204, 1148 cm-1; [R]25 +0.051 (c 0.4,
D
CH2Cl2); mp 135-137 °C.
{2-P h en yl-1-[(p yr id in -4-ylm et h yl)ca r b a m oyl]-et h yl}-
ca r b a m ic Acid 4-(3,3,4,4,5,5,6,6,7,7,8,8,8-Tr id eca flu or o-
1
octyl) Ben zyl Ester (Ta ble 2, en tr y 6). H NMR (CDCl3) δ
8.45 (d, J ) 3.81 Hz, 2H), 7.28-6.91 (m, 11H), 6.38 (br, 1H),
5.45 (br, 1H), 5.05 (s, 2H), 4.47 (dd, J ) 14.6, 7.63 Hz, 1H),
4.39 (dd, J ) 15.9, 6.22 Hz, 1H), 4.28 (dd, J ) 15.9, 5.80 Hz,
1H), 3.16 (dd, J ) 13.7, 6.26 Hz, 1H), 3.05 (dd, J ) 13.6, 7.92
Hz, 1H), 2.94-2.88 (m, 2H), 2.44-2.26 (m, 2H); 19F NMR
(CDCl3) δ -79.5 (3F), -113.4 (2F), -120.6 (2F), -121.6 (2F),
-122.2 (2F), -124.9 (2F); 13C NMR (CDCl3) δ 171.4, 156.2,
150.1, 146.9, 139.4, 135.9, 134.3, 128.9-127.5 (m), 122.2-110.9
(m), 66.7, 56.3, 41.8, 38.6; LRMS m/z (rel intensity) 454 (84),
451 (100), 437 (18), 281 (29); HRMS calcd for C31H26F13N3O3
735.1766, found 735.1785; IR (KBr) 3303, 1696, 1651, 1531,
1
identified by H, 13C, and 19F NMR and mass spectroscopy as
identical with the products in Table 2.
Rea ction of th e Mixtu r e of 1 a n d 2 w ith 1,2,3,4-
Tetr a h yd r oisoqu in olin e a n d Sep a r a tion of 3 a n d 4 fr om
th e Rea ction Mixtu r e by P r ep a r a tive HP LC. After reac-
tion as above, the solvents were evaporated and the crude
reaction mixture (290.2 mg) was dissolved in 2 mL of aceto-
nitrile and injected in two 1-mL portions onto a preparative
FluoroFlash HPLC column. The column was eluted with 80/
20 acetonitrile/H2O increasing to 100% acetonitrile for 30 min.
The fractions of products were collected and evaporated to give
3b (49.1 mg, 83%) and 3a (53.9 mg, 81%) separately, which
1256, 1137 cm-1; [R]25 -0.000075 (c 0.4, CH2Cl2); mp 164-
D
165 °C.
{2-P h en yl-1-[(p yr id in -4-ylm et h yl)ca r b a m oyl]et h yl}-
ca r ba m ic Acid 4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Hep -
ta d eca flu or od ecyl) Ben zyl Ester (Ta ble 2, en tr y 5): 1H
NMR (CDCl3) δ 8.48 (d, J ) 5.65 Hz, 2H), 7.30-6.98 (m, 11H),
6.16 (br, 1H), 5.30 (br, 1H), 5.08 (s, 2H), 4.45-4.30 (m, 3H),
3.18 (dd, J ) 13.4, 5.79 Hz, 1H), 3.05 (dd, J ) 13.4, 7.89 Hz,
1H), 2.95-2.89 (m, 2H), 2.44-2.26 (m, 2H); 19F NMR (CDCl3)
δ -79.5 (3F), -113.4 (2F), -120.7 (6F), -121.5 (2F), -122.2
(2F), -124.9 (2F); 13C NMR (CDCl3) δ 171.1, 149.7, 147.0,
139.5, 136.2, 134.5, 129.4-127.3 (m), 122.2-110.9 (m), 66.7,
56.3, 42.3, 38.6; LRMS m/z (rel intensity) 554 (13), 537 (15),
281 (11); HRMS calcd. for C33H26F17N3O3 835.1702, found
1
were identified by H and 19F NMR spectroscopy.
[1-Ben zyl-2-(3,4-d ih yd r o-1H -isoq u in olin -2-yl)-2-oxo-
eth yl]ca r ba m ic Acid Ben zyl Ester Cbz-P h e-THQ. To a
solution of N-(carbobenzyloxy)-L-phenylalanine (20 mg, 0.067
mmol), EDCI (19.2 mg, 0.10 mmol), and HOBt (13.5 mg, 0.10
mmol) in chloroform/DMF (0.65 mL/0.65 mL) was added
1,2,3,4-tetrahydroisoquinoline (33.4 µL, 0.267 mmol) and tri-
ethylamine (13.9 µL, 0.100 mmol). The mixture was stirred
at room temperature for 2 h. The reaction mixture was diluted
with ether and 5% HCl (4 mL) was added. The organic layer
was extracted with ethyl acetate three times and dried over
magnesium sulfate. Magnesium sulfate was filtered off and
after evaporation of solvents, the residue was purified by
column chromatography with 2/1 pentane/ethyl acetate to give
product (27.0 mg, 98%) as a white oil: 1H NMR (CDCl3) δ
7.35-6.86 (m, 14H), 5.79 (br, 1H), 5.10 (s, 2H), 4.98 (dd, J )
15.6, 7.63 Hz, 1H), 4.66 (dd, J ) 55.8, 17.1 Hz, 1H), 4.23 (dd,
J ) 152, 15.9 Hz, 1H), 3.86-3.62 (m, 1H), 3.59-3.09 (m, 1H),
3.06-2.95 (m, 2H), 2.83-2.72 (m, 2H).
HP LC An a lysis of th e Mixtu r e of 3a , 3b, a n d Cbz-P h e-
THQ (Cbz-P h e-THQ is th e sta n d a r d , n on flu or ou s Cbz
a n a logu e of 3a a n d 3b). The equimolar mixture of 3a , 3b,
and Cbz-P h e-THQ was injected onto an analytical HPLC
column. The column was eluted with 80/20 acetonitrile/H2O
increasing to 100% acetonitrile over 30 min. Compounds 3a ,
3b, and Cbz-P h e-THQ eluted individually at 16.0, 5.2, and
1.9 min.
835.1792; IR (KBr) 3301, 1696, 1652, 1533, 1204, 1146 cm-1
;
[R]25 +0.00725 (c 0.4, CH2Cl2); mp 167-169 °C.
D
[2-P h en yl-1-(3-tr iflu or om eth ylben zylca r ba m oyl)eth yl]-
ca r b a m ic Acid 4-(3,3,4,4,5,5,6,6,7,7,8,8,8-Tr id eca flu or o-
1
octyl) Ben zyl Ester (Ta ble 2, en tr y 8). H NMR (CDCl3) δ
7.53-7.14 (m, 11H), 6.13 (br, 1H), 5.40 (br, 1H), 5.07 (s, 2H),
4.42-4.34 (m, 3H), 3.16 (dd, J ) 13.6, 6.05 Hz, 1H), 3.02 (dd,
J ) 13.6, 7.92 Hz, 1H), 2.96-2.85 (m, 2H), 2.44-2.26 (m, 2H);
19F NMR (CDCl3) δ -61.3 (3F), -79.5 (3F), -113.3 (2F), -120.6
(2F), -121.6 (2F), -122.3 (2F), -124.9 (2F); 13C NMR (CDCl3)
δ 171.0, 156.0, 150.1, 139.4-110.7 (m), 66.9, 56.6, 43.1, 38.6,
32.9, 26.2; LRMS m/z (rel intensity) 600 (5), 454 (60), 437 (80),
305 (49), 159 (50); IR (KBr) 3297, 1690, 1660, 1528, 1330, 1247,
1134 cm-1; [R]25 -0.0218 (c 0.4, CH2Cl2); mp 134-135 °C.
D
[2-P h en yl-1-(3-tr iflu or om eth ylben zylca r ba m oyl)eth yl]-
ca r ba m ic Acid 4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Hep -
ta d eca flu or od ecyl) Ben zyl Ester (Ta ble 2, en tr y 7). 1H
NMR (CDCl3) δ 7.53-7.17 (m, 11H), 6.01 (br, 1H), 5.33 (br,
1H), 5.06 (s, 2H), 4.44-4.38 (m, 3H), 3.17 (dd, J ) 13.6, 6.00
Hz, 1H), 3.02 (dd, J ) 13.5, 7.90 Hz, 1H), 2.94-2.89 (m, 2H),
2.44-2.27 (m, 2H); 19F NMR (CDCl3) δ -61.3 (3F), -79.5 (3F),
-113.3 (2F), -120.4 (2F), -120.6 (4F), -121.4 (2F), -122.2
(2F), -124.8 (2F); 13C NMR (CDCl3) δ 170.9, 156.0, 139.4-
107.5 (m), 66.9, 53.5, 43.1, 38.6, 32.9, 26.2; LRMS m/z (rel
intensity) 554 (18), 536 (44), 305 (25), 159 (29); HRMS calcd
for C35H26F20N2O3 ???, found, XXX. IR (KBr) 3303, 1690, 1660,
1529, 1330, 1248, 1205, 1142 cm-1; [R]25D +0.0265 (c 0.4, CH2-
Cl2); mp 142-144 °C.
Ack n ow led gm en t. D.P.C. thanks the National In-
stitute of Health for funding this work. D.G. thanks the
NSF for an REU Summer Fellowship.
Su p p or tin g In for m a tion Ava ila ble: Tables of HRMS
data, optical rotations, and melting points of all the FCbz
1
derivatives along with copies of all H and 13C NMR spectra
and two representative IR spectra. This material is available
free of charge via the Internet at http://pubs.acs.org.
J O0344283
J . Org. Chem, Vol. 68, No. 12, 2003 4647