DesVI: A new member of the sugar N,N-dimethyltransferase family involved in the biosynthesis of desosamine

Article abstract of DOI:10.1002/1521-3773(20000616)39:12<2160::AID-ANIE2160>3.0.CO;2-E

Purification and characterization of a new enzyme belonging to the amino sugar N,N-dimethyltransferase family has been achieved. DesVI catalyzes the successive transfer of two methyl groups in the biosynthetic pathway of desosamine (see scheme), an unusua

Full text of DOI:10.1002/1521-3773(20000616)39:12<2160::AID-ANIE2160>3.0.CO;2-E

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instead, presumably by means of b-H elimination.[7] As shown
also in Scheme 3, activation of EtOPh by 1 (toluene, 1108C,
2 h) gave compound 6 (see Supporting Information). It thus
appears that the very important steric demands of the Tpx
ligand (as compared with the somewhat less bulky cyclo-
pentadienyl ligand, Cpx) and its rigid nature, which tends to
enforce six-fold coordination to the metal center, favors a-H
elimination over b-H elimination in the transformations
studied here.
Â
Nicasio, P. J. Perez, M. L. Poveda, E. Carmona, Chem. Eur. J. 1998, 4,
2225.
[5] a) A. Sen, M. Lin, L.-C. Kao, A. C. Hutson, J. Am. Chem. Soc. 1992,
114, 6385; b) Z.-W. Li, H. Taube, J. Am. Chem. Soc. 1994, 116, 11584.
[6] R. R. Schrock, S. W. Seidel, N. C. Mösch-Zanetti, K.-Y. Shih, M. B.
OꢁDonoghue, W. M. Davis, W. M. Reiff, J. Am. Chem. Soc. 1997, 119,
11876.
[7] a) B. A. Arndtsen, R. G. Bergman, Science, 1995, 270, 1970; b) H. F.
Luecke, B. A. Arndtsen, P. Burger, R. G. Bergman, J. Am. Chem. Soc.
1996, 118, 2517.
Â
[8] E. Gutierrez-Puebla, A. Monge, M. Paneque, M. L. Poveda, V.
In summary, we have shown that the IrI compound 1 effects
Salazar, E. Carmona, J. Am. Chem. Soc. 1999, 121, 248.
[9] C. Slugovc, K. Mereiter, S. Trofimenko, E. Carmona, Chem. Commun.
2000, 121.
À
the regioselective, double C H activation of a variety of ether
and amine substrates by allowing their precoordination to the
metal center. The formation of Fischer-type carbenes in this
cascade activation (cyclometalation-b-elimination (or vice
versa)-a-elimination) is made possible by the presence of an
adequate hydrogen-accepting leaving group. The Tpx- and
Cpx-Ir systems reported herein include O and N heteroatoms.
Comparative studies on the facility of these fundamental
organometallic reactions (a- and b-eliminations) on closely
related Tpx- and Cpx-Ir systems without these heteroatoms
that could alter the relative energies of the transition states
and intermediates,[17] are presently in progress and will be
reported in due course.
[10] The related compound [Ir(k4(N,N',N'',CPh)-TpPh)(Et)(h2-C2H4)] acti-
vates THF to give 2 but with the other ether or amine substrates
employed in this work the reaction failed due to the formation of
[Ir(k5(N,N',N'',CPh,CPh')-TpPh)(h2-C2H4)].[9]
[11] C. Six, B. Gabor, H. Görls, R. Mynott, P. Philipps, W. Leitner,
Organometallics, 1999, 18, 3316.
[12] Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Center as supplementary publication no.
CCDC- 139166. Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK
(fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
[13] D. M. Heinekey, J. M. Millar, T. F. Koetzle, N. G. Payne, K. W. Zilm, J.
Am. Chem. Soc. 1990, 112, 909, and references therein.
[14] U. E. Bucher, A. Currao, R. Nesper, H. Rüegger, L. M. Venanzi, E.
Younger, Inorg. Chem. 1995, 34, 66.
[15] Y. Kataoka, M. Imanishi, T. Yamagata, K. Tani, Organometallics 1999,
18, 3563.
Experimental Section
[16] M. W. Holtcamp, J. A. Labinger, J. E. Bercaw, J. Am. Chem. Soc. 1997,
119, 848.
[17] J. Jaffart, R. Mathieu, M. Etienne, J. E. McGrady, O. Eisenstein, F.
Maseras, Chem. Commun. 1998, 2011.
1: To a suspension of [(IrCl(coe)2)2] (175 mg, 0.20 mmol) in CH2Cl2 (6 mL),
2-methylbutadiene (0.3 mL, excess) was added at room temperature to give
a colorless solution. A solution of TlTpPh (253 mg, 0.40 mmol) in CH2Cl2
(6 mL) was then added. Stirring the reaction mixture for 4 h at room
temperature resulted in the precipitation of TlCl. After filtration, the clear
solution was evaporated to dryness. The crude product (orange powder)
was purified via column chromatography (neutral aluminum oxide 90%
activated, eluents PE (petroleumether):Et2O ˆ 15:1, eluted as a pale violet
band). Compound 1 was obtained upon changing the eluents to PE:Et2O ˆ
4:1 and it eluted as a yellow band. Removing the solvent and drying in
vacuum gave pure 1. Yield: 198mg (71%). Elemental analysis: calcd for
C32H30BIrN6 (%): C 54.8, H 4.3, N 12.0; found: C 54.4, H 4.1, N 12.2.
DesVI: A New Member of the Sugar
N,N-Dimethyltransferase Family Involvedin
the Biosynthesis of Desosamine**
Compounds 2 ± 6 can be prepared similarly by treating 1 with an excess of
the corresponding ether or amine. As a representative example the
synthesis of 5 is given: A solution of 1 (70 mg, 0.10 mmol) in Et2O was
heated at 608C for 12 h. The solution was evaporated to dryness.
Purification by flash chromatography (neutral aluminum oxide 90%
activated, eluents PE:Et2O ˆ 2:1, eluted as a yellow band) resulted in pure
5. Yield: 58mg (82%). Elemental analysis: calcd for C 31H30BIrN6O (%): C
52.8, H 4.3, N 11.9; found: C 53.0, H 4.6, N 11.7.
Cheng-wei Chang, Lishan Zhao, Hiroshi Yamase, and
Hung-wen Liu*
Methylation catalyzed by S-adenosylmethionine (AdoMet)
dependent enzymes is one of the most common reactions
occurring in biological systems. While a large number of
methyltransferases which catalyze methylation at carbon,
Received: January 28, 2000 [Z14616]
[1] a) S. S. Stahl, J. A. Labinger, J. E. Bercaw, Angew. Chem. 1998, 110,
2298; Angew. Chem. Int. Ed. 1998, 37, 2181; b) B. A. Arndtsen, R. G.
Bergman, T. A. Mobley, T. H. Peterson, Acc. Chem. Res. 1995, 28, 154;
c) J. C. W. Lohrenz, H. Jacobsen, Angew. Chem. 1996, 108, 1403;
Angew. Chem. Int. Ed. Engl. 1996, 35, 1305.
[*] Prof. Dr. H.-w. Liu, C.-w. Chang,[‡] L. Zhao, H. Yamase
Department of Chemistry
University of Minnesota, Minneapolis, MN 55455 (USA)
Fax : (‡1)612-626-7541
[2] a) F. Zaragoza Dörwald, Metal Carbenes in Organic Synthesis, Wiley-
VCH, Weinheim, 1999; b) K. H. Dötz, H. Fischer, P. Hofmann, R. R.
Kreissl, U. Schubert, K. Weiss, Transition Metal Carbene Complexes,
VCH, Weinheim, 1993.
E-mail: liu@chem.umn.edu
‡
[ ] Current address:
[3] For gas phase FeI-mediated 1,1-elimination of H2 from a methoxy
group, see: T. Prüsse, A. Fiedler, H. Schwarz, J. Am. Chem. Soc. 1991,
113, 8335.
Department of Chemistry and Biochemistry
Utah State University, Logan, UT 84322 (USA)
[**] The authors gratefully acknowledge financial support provided by the
National Institutes of Health (GM 54346). H.-w.L. also thanks the
National Institute of General Medical Sciences for a MERIT Award.
L.Z. is the recipient of a Graduate School Dissertation Fellowship
from the University of Minnesota.
[4] a) H. Werner, B. Weber, O. Nürnberg, J. Wolf, Angew. Chem. 1992,
104, 1079; Angew. Chem. Int. Ed. Engl. 1992, 31, 1025; b) O. Boutry, E.
Â
Â
Gutierrez, A. Monge, M. C. Nicasio, P. J. Perez, E. Carmona, J. Am.
Â
Chem. Soc. 1992, 114, 7288; c) E. Gutierrez-Puebla, A. Monge, M. C.
2160
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oxygen, sulfur, and nitrogen atoms are known, only a few are
capable of catalyzing N,N-dimethylation.[1] Our knowledge of
these enzymes is scarce as most of them have never been
isolated and fully characterized. Recently, genetic studies of
the biosynthesis of desosamine (1), a structural component of
the antibiotics methymycin (2), neomethymycin (3), pikro-
mycin, and narbomycin produced by Streptomyces venezue-
lae,[2] have led to the tentative assignment of desVI in the
methymycin/pikromycin biosynthetic gene cluster as a candi-
date for encoding a new N,N-dimethyltransferase.[3] The
DesVI protein presumably acts on the C-3 amino group of
sugar substrate 4 to give TDP-desosamine (5, see Scheme 1).
The fact that disruption of the desVI gene in the genome of S.
venezuelae resulted in the formation of a series of macrolides
carrying an amino sugar devoid of N,N-dimethylation pro-
vided initial evidence to indicate that desVI indeed encodes an
N,N-dimethyltransferase.[4]
buffers containing 0.1mm dithiothreitol (DTT) and 0.1mm
AdoMet. Further analysis using size-exclusion chromatogra-
phy (Superdex 200 resin) revealed that DesVI exists as a
homodimer with a subunit molecular mass of 28.1 kDa.[6] The
UV/Vis spectrum of the purified enzyme is transparent above
300 nm.
The predicted substrate of DesVI, 4, was synthesized from
methyl 4,6-O-benzylidene-glucoside (6) as depicted in
Scheme 2. Preparation of the first key intermediate 9 was
Scheme 1.
Scheme 2. a) 1. (nBu3Sn)2O, toluene; 2. BnBr; b) 1. Ac2O, pyridine;
2. HOAc, H2O; c) SO2Cl2, CHCl3, pyridine; d) nBu3SnH, AIBN, toluene;
e) 1. NaOMe, MeOH; 2. (COCl)2, DMSO, DIPEA, CH2Cl2; 3. NaBH4,
MeOH; f) (PhO)2P(O)N3, Ph3P, DEAD, THF; g) BBr3, CH2Cl2;
h) 1. iPr2NP(OBn)2, 1H-tetrazole, MeCN; 2. mCPBA, CH2Cl2; i) H2,
Pd(OH)2/C, NaHCO3, MeOH; j) 1H-tetrazole, TMP-morpholidate, pyr-
idine. Bn ˆ benzyl, AIBN ˆ azobisisobutyronitrile, DIPEA ˆ diisopropyl-
ethylamine, DEAD ˆ diethylazodicarboxylate, mCPBA ˆ meta-chloroper-
oxybenzoic acid, TMP ˆ thymidine-5'-(trihydrogenphosphate), TDP ˆ
thymidine-5'-(dihydrogenphosphate).
To further verify the proposed role of the desVI gene, we
have now expressed and purified its encoded product, and
characterized the catalytic function of this protein. In this
paper, we report chemical evidence which establishes the role
of DesVI enzyme as the methyltransferase catalyzing the N,N-
dimethylation, the last step in the biosynthesis of desosamine.
The N,N-dimethylation of the C-3 amino group in 4 rendered
the product 5 more susceptible to protonation, a modification
essential for enhancing the binding affinity of the resulting
macrolide antibiotic toward its negatively charged 23S
ribosomal RNA target.[5]
To study the function of DesVI, the desVI gene was
amplified by the polymerase chain reaction (PCR) and cloned
into the NdeI/EcoRI sites of the expression vector
pET28b(‡). The resulting plasmid was used to transform
Escherichia coli BL21(DE3) cells, and the recombinant strain
was grown at 308C in LB (Luria-Bertani) medium. Induc-
tion of protein expression was achieved by the addition of
0.1mm isopropyl b-D-thiogalactoside (IPTG). The DesVI
enzyme, tagged with His6 at its N terminus, was purified to
near homogeneity using Ni ± nitrilotriacedic acid (Ni ± NTA)
resin (Qiagen), and was found to be stable in phosphate
initiated by a selective monobenzylation mediated by bis-
(tributyltin) oxide (7:8 ˆ 8:1),[7] followed by acetylation,
deprotection, dichlorination, and reduction with an overall
yield of 14%. After hydrolysis, the configuration of 3-OH was
inverted by a Swern oxidation and NaBH4 reduction (77%
yield from 9). The amino group, masked as an azide moiety,
was introduced at C-3 of 10 under Mitsunobu conditions to
give 11 in 81% yield. Subsequent demethylation was effected
by BBr3 at low temperature (À78to 0 8C), and the product
was benzylphosphorylated to give 12 (34% yield). The final
steps involved hydrogenation of 12 with Pd(OH)2, Degussa
type,[8] and coupling of the resulting product with TMP-
morpholidate.[9] Compound 4 was purified by a Bio-P2
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column (eluted with 25mm NH4HCO3), and then MonoQ fast
protein liquid chromatography (FPLC; linear gradient elution
from 0 to 0.5m NH4HCO3).[10]
To facilitate confirmation of the enzymatic product struc-
ture, a convenient protocol to make the expected product,
TDP-desosamine (5), was also developed. As delineated in
Scheme 3, the preparation began with the acid hydrolysis of
HPLC peaks, and by fitting these data to the rate laws for an
irreversible unimolecular consecutive reaction (4 !16 !5)
led to the constants of 0.005 and 0.82 minÀ1 for the mono- and
dimethylation steps, respectively. Thus, our results clearly
demonstrate that DesVI is the required methyltransferase in
the biosynthesis of desosamine, and it alone catalyzes the N,N-
dimethylation of the 3-amino group of 4 in a stepwise manner.
In summary, the above results have clearly established
DesVI as a new member of the small family of enzymes that
are capable of catalyzing N,N-dimethylation.[1] It should be
pointed out that the deduced sequence of DesVI reveals
significant similarity to those of EryCVI from the erythro-
mycin cluster of Saccharopolyspora erythraea (62% identi-
ty),[3] OleM1 from the oleandomycin cluster of Streptomyces
antibioticus (61%),[13] TylM1 from the tylosin cluster of
Streptomyces fradiae (60% identity),[14] SnoX from the
nogalamycin cluster of Streptomyces nogalater (55% iden-
tity),[15] RdmD from the rhodomycin cluster of Streptomyces
purpurascens (57% identity),[16] and SrmX from the spiramy-
cin cluster of Streptomyces ambofaciens (57% identity).[17]
The catalytic role of TylM1 as an AdoMet-dependent N,N-
dimethyltransferase has recently been verified.[18] The fact
that DesVI also acts on the amino group of a sugar substrate
in a similar manner provides convincing evidence suggesting
similar roles for these proteins in their respective biosynthetic
pathways. The N,N-dimethylation of amino sugars could be a
convenient tool to modify their chemical properties due to the
changes in size, hydrogen-bonding capacity, and propensity
for protonation of the amino group. Therefore, with the
addition of DesVI and the expectation that other similar
methyltransferases will be added in the future to the arsenal of
biosynthetic genes, the ability to prepare designed glycocon-
jugate analogues with novel tailored biological activities
should be enhanced significantly.
Scheme 3. a) 1. 6n HCl, H2O, EtOH, reflux; 2. Ac2O, H2SO4; b) 1. H3PO4,
P2O5; 2. 2m LiOH; c) TMP-morpholidate, 1H-tetrazole, pyridine.
the commercially available erythromycin B (13).[11] The
released desosamine was directly acetylated to give 14 in
89% yield. The crude product was relatively labile at room
temperature; however, it was rendered more stable after
neutralization by dissolving in dichloromethane and washing
with ammonium hydroxide and water. Direct phosphorylation
of 14 using crystalline phosphoric acid followed by alkaline
hydrolysis with lithium hydroxide afforded desosamine
1-phosphate (15) as a mixture of a- and b-anomers. The
crude mixture was loaded onto a Dowex-50W column (cyclo-
hexylammonium ion form) and eluted with water. The desired
a-anomer of 15 was obtained in 12% yield after further
purification by a Bio-P2 column (eluted with water). The
subsequent coupling with TMP-morpholidate and the purifi-
cation of the desired product 5 followed a procedure which
was analogous with the synthesis of 4.[12]
To test whether DesVI is the desired methyltransferase, the
purified DesVI (20 mg) was incubated with 4 (0.06 mmol),
AdoMet (0.5 mmol), and DTT (2mm) at 278C for 3 h in 50mm
potassium phosphate buffer (50 mL, 10% glycerol, pH 7.5).
The incubation mixture was analyzed by HPLC with an
Adsorbsphere SAX column (5 m, 4.6 Â 250 mm) using a linear
gradient from 140 to 320 mm potassium phosphate buffer
(pH 3.5) over 20 min. Detection was at 267 nm, and the flow
rate was 1.0 mLminÀ1. It was found that greater than 80% of
4, which has a retention time of 6.5 min, was consumed and a
new peak appeared at 17.0 min. A subsequent large scale
incubation of 1.8mg of DesVI, 4 (5.7 mmol), AdoMet
(30 mmol), and DTT (2mm) in 1 mL of the same buffer at
258C for 3 h allowed the isolation and purification of this new
compound. Spectral characterization confirmed that the
purified product is indeed the desired TDP-desosamine (5).
When the reaction was quenched (boiled for 2 min) at an
earlier time, an intermediate with a retention time of 9.3 min,
presumably the monomethylated species 16, could also be
detected. The percentage conversions of 4 to 16 and 5 were
estimated based on the integration of the corresponding
Received: December 16, 1999 [Z14408]
[1] a) T. Kodaki, S. Yamashita, Eur. J. Biochem. 1989, 185, 243 ± 251;
b) J. D. Gary, W.-J. Lin, M. C. Yang, H. R. Herschman, S. Clarke, J.
Biol. Chem. 1996, 271, 12585 ± 12594; c) M. Zalacain, E. Cundliffe, J.
Bacteriol. 1989, 171, 4254 ± 4260.
[2] a) M. N. Donin, J. Pagano, J. D. Dutcher, C. M. McKee, Antibiot.
Annu. 1953 ± 1954, 1, 179 ± 185; b) C. Djerassi, J. A. Zderic, J. Am.
Chem. Soc. 1956, 78, 6390 ± 6395.
Â
[3] a) S. Gaisser, G. A. Bohm, J. Cortes, P. F. Leadlay, Mol. Gen. Genet.
1997, 256, 239 ± 251; b) R. G. Summers, S. Donadio, M. J. Staver, E.
Wendt-Pienkowski, C. R. Hutchinson, L. Katz, Microbiology 1997,
143, 3251 ± 3262; c) Y. Xue, L. Zhao, H.-w. Liu, D. H. Sherman, Proc.
Natl. Acad. Sci. USA. 1998, 95, 12111 ± 12116.
[4] L. Zhao, D. H. Sherman, H.-w. Liu, J. Am. Chem. Soc. 1998, 120,
10256 ± 10257.
[5] H. Sakakibara, S. Omura, Macrolide Antibiotics, Chemistry, Biology
and Practice (Ed.: S. Omura), Academic Press, New York, 1984,
Chapter 3, pp. 85 ± 125.
[6] The molecular mass of each subunit calculated, based on the
translated DesVI sequence together with its His6 tag, is 28,110 Da.
[7] F. Dasgupta, P. J. Garegg, Synthesis 1994, 1121 ± 1123.
[8] R. Wischnat, R. Martin, C.-H. Wong, J. Org. Chem. 1998, 63, 8361 ±
8365.
[9] V. Wittmann, C.-H. Wong, J. Org. Chem. 1997, 62, 2144 ± 2147.
[10] Spectral data for 4: 1H NMR (500 MHz, D2O) d ˆ 1.24 (3H, d, J ˆ
6.3 Hz, 5-Me), 1.50 (1H, ddd, J ˆ 12.7, 12.3, 11.7 Hz, 4-Hax), 1.93 (3H,
s, 5''-Me), 2.27 (1H, ddd, J ˆ 12.7, 4.0, 3.0 Hz, 4-Heq), 2.40 (2H, m, 2'-
H), 3.59 (1H, ddd, J ˆ 12.2, 10.7, 4.0 Hz, 3-H), 3.74 (1H, dt, J ˆ 10.7,
2162
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2.9 Hz, 2-H), 4.20 (3H, m, 4'-H, 5'-H), 4.29 (1H, ddq, J ˆ 11.7, 6.3,
3.0 Hz, 5-H), 4.62 (1H, dt, J ˆ 5.8, 3.0 Hz, 3'-H), 5.63 (1H, dd, J ˆ 7.3,
3.4 Hz, 1-H), 6.35 (1H, t, J ˆ 6.8Hz, 1 '-H), 7.71 (1H, s, 6''-H);
13C NMR (125 MHz, D2O) d ˆ 11.6, 19.5, 35.3, 38.5, 48.9, 65.4, 69.5 (d,
J ˆ 6.6), 70.9, 84.9, 85.0, 85.3 (d, J ˆ 10.1), 95.0 (d, J ˆ 8.0), 111.7, 137.3,
151.7, 166.5; 31P NMR (121 MHz, D2O) d ˆ À12.4 (d, J ˆ 20.9), À10.5
(d, J ˆ 20.9); high-resolution fast atom bombardment (FAB) MS:
transferring the absorbed energy to a nearby secondary
energy acceptor species. The energy-transfer process is
influenced by the spatial relationship of the donor and
acceptor chromophores, and recently researchers have sought
to mimic the efficient arrangements found in nature. These
include chromophore-functionalized polymers,[1] dendrim-
ers,[2] supported Langmuir± Blodgett films,[3] thin films,[4]
and microspheres.[5] Here, we report the use of self-assembled
monolayers (SAMs) to align the donor and acceptor chro-
mophores and facilitate intermolecular energy transfer.
Intermolecular interactions between adjacent adsorbates
have previously been applied to improve the chemical
stability of monolayers[6] and to facilitate surface-directed
polymerization[7] or surface-confined photodimerization.[8]
We extend the exploration of these interactions to include
long-range photo-induced Förster energy transfer[9] between
donor and acceptor chromophores on SAMs. This process
involves a through-space dipole ± dipole interaction that does
not occur by ªhoppingº through bonds. Energy transfer can
thus be facilitated by assembly of donor and acceptor
chromophores as mixed monolayers.
‡
‡
calcd for C16H28N3O13P2 [M ‡ 2H] 532.1097, found [M ‡ 2H]
532.1098.
[11] E. H. Flynn, M. V. Sigal, Jr., P. E. Wilex, K. Gerzon, J. Am. Chem. Soc.
1954, 76, 3121 ± 3131.
[12] Spectral data for 5: 1H NMR (500 MHz, D2O) d ˆ 1.24 (3H, d, J ˆ
6.4 Hz, 5-Me), 1.62 (1H, dt, J ˆ 12.7, 11.7 Hz, 4-Hax), 1.90 (3H, s, 5''-
Me), 2.12 (1H, dt, J ˆ 12.7, 3.4 Hz, 4-Heq), 2.3 ± 2.4 (2H, m, 2'-H), 2.83
(6H, s, NMe2), 3.76 (1H, dt, J ˆ 11.7, 3.4 Hz, 3-H), 3.88 (1H, dt, J ˆ
11.2, 2.9 Hz, 2-H), 4.1 ± 4.2 (3H, m, 4'-H, 5'-H), 4.28(1H, ddq, J ˆ 11.7,
6.4, 3.4 Hz, 5-H), 4.59 (1H, dt, J ˆ 5.4, 3.4 Hz, 3'-H), 5.64 (1H, dd, J ˆ
7.1, 3.1 Hz, 1-H), 6.33 (1H, t, J ˆ 6.8Hz, 1 '-H), 7.70 (1H, s, 6''-H);
13C NMR (125 MHz, D2O) d ˆ 11.6, 19.7, 29.1, 38.5, 38.6 (broad,
NMe2), 62.0, 65.5 (d, J ˆ 5.1 Hz), 65.8, 66.7 (d, J ˆ 8.1), 70.9, 84.9, 85.2
(d, J ˆ 10.1), 95.2 (d, J ˆ 6.0), 111.7, 137.3, 151.7, 166.5; 31P NMR
(121 MHz, D2O) d ˆ À12.4 (d, J ˆ 20.8), À10.6 (d, J ˆ 20.8); high-
‡
resolution FAB MS: calcd for C18H30N3O13P2 [M ‡ 2H] 560.1410,
‡
found [M ‡ 2H] 560.1400.
[13] C. Olano, A. M. Rodriguez, J. M. Michel, C. Mendez, M. C. Raynal,
J. A. Salas, Mol. Gen. Genet. 1998, 259, 299 ± 308.
We have recently reported efficient light harvesting by
chromophore-labeled dendrimers in which light is funneled
through space by Förster energy transfer from multiple
coumarin-2 (1) donor dyes at the dendrimer periphery to a
single coumarin-343 (2) acceptor chromophore.[10] These dyes
were also chosen for our chromophore-labeled monolayers
[14] A. R. Gandecha, S. L. Large, E. Cundliffe, Gene 1997, 184, 197 ± 203.
[15] K. Ylihonko, J. Tuikkanen, S. Jussila, L. Cong, P. Mäntsälä, Mol. Gen.
Genet. 1996, 251, 113 ± 120.
[16] J. Niemi, P. Mäntsälä, J. Bacteriol. 1995, 177, 2942 ± 2945.
[17] M. Geistlich, R. Losick, J. R. Turner, R. N. Rao, Mol. Microbiol. 1992,
6, 2019 ± 2029.
[18] H. Chen, Z. Guo, H.-w. Liu, J. Am. Chem. Soc. 1998, 120, 9951 ± 9952.
Surface-ConfinedLight Harvesting, Energy
Transfer, andAmplification of Fluorescence
Emission in Chromophore-Labeled
Self-AssembledMonolayers**
Lysander A. J. Chrisstoffels, Alex Adronov, and
Â
Jean M. J. Frechet*
Light harvesting and energy transfer have received consid-
erable attention in the literature because of their important
role in natural photosynthesis. These processes involve the use
of a light-absorbing antenna (donor) moiety that is capable of
Â
[*] Prof. J. M. J. Frechet, L. A. J. Chrisstoffels, A. Adronov
Department of Chemistry, 718Latimer Hall
University of California at Berkeley
Berkeley, CA 94720-1460 (USA)
and
Division of Material Sciences
Lawrence Berkeley National Laboratory
Berkeley, CA 94720 (USA)
Fax : (‡1)510-643-3079
E-mail: frechet@cchem.berkeley.edu
[**] This research was supported by the office of Naval Research, the
AFOSR ± MURI program, as well as fellowships from the Nether-
lands Scientific Organization (NWO), and from the Eastman Kodak
Company, which are gratefully acknowledged.
Supporting information for this article is available on the WWW under
http://www.wiley-vch.de/home/angewandte/ or from the author.
Angew. Chem. Int. Ed. 2000, 39, No. 12
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
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