R. Frei and H. E. Blackwell
7a,b and 50 structurally divergent aryl-iodides (9; see Sup-
porting Information for structures) as library building
blocks. The stilbene products (11a,b) were isolated in
ꢁ100 nmol per spot quantities, which was more than suffi-
cient for analytical testing and numerous biological assays.[5]
A subset of the library (20 randomly selected compounds)
was evaluated by HPLC, and high product conversions and
purities were obtained in almost all cases (Table 1).[31] These
results are significant, as they represent to our knowledge
the first demonstration of metal-mediated coupling reactions
in small molecule macroarray synthesis. Notably, we were
able to prepare the 100 stilbenes (11a,b) in under 12 h start-
ing from unfunctionalized cellulose 2 (including all reac-
tions, washing, drying, cleavage, and compound elution), fur-
ther highlighting the efficiency of this synthesis method for
the generation of libraries of biologically relevant mole-
cules.
Figure 2. Luminescence (LuxR) inhibition data for the five most potent
stilbenes in library 11a,b (1:1 against OHHL; 5 mm compound). Two of
the most active stilbenes are shown. Strain: V. fischeri ES114 (D-luxI).
Neg. control=DMSO. Pos. control=OHHL. Assays performed in tripli-
cate (see Supp. Info. for assay protocol and full stilbene structures).
V. fischeri mutant strain comparable to some of the most
potent known native and non-native LuxR antagonists (e.g.,
N-(3-oxo-dodecanoyl)-l-homoserine lactone (OdDHL);
Figure 2).[19] Indeed, these stilbenes were capable of inhibit-
ing LuxR by ꢂ 80% at a 1:1 ratio against OHHL. Addi-
tional experiments are required to elucidate the mechanism
by which these stilbenes elicit their LuxR inhibitory effects.
Nevertheless, these screening data suggest that stilbenes
with structures beyond the resveratrol (1) scaffold are capa-
ble of modulating QS responses. Few compounds with struc-
tures dissimilar to native QS signals have been shown to in-
terfere with QS;[18,20] therefore, the discovery of these active
ligands from such a small library of compounds (100-
member) is noteworthy.
Table 1. Representative purity and conversion data for the stilbene mac-
roarray products 11a,b.
Stilbene R1
R2
R3
R4
R5
Conversion
[%][a]
Purity
[%][b]
11a-4
H
H
H
H
H
H
NO2
H
NO2
CN
H
H
F
F
CF3
H
NO2
H
CN
H
H
F
F
NO2
CF3
CH2CN
H
CN
H
H
CH3
H
H
CH3
H
CH2CN
H
CN
H
CH3
H
H
CH3
H
H
H
NO2
H
H
H
H
H
H
H
99
95
98
99
92
94
97
98
98
96
93
88
87
88
92
94
99
97
96
93
88
92
93
94
11a-15
11a-22
11a-26
11a-27
11a-38 NO2
11a-41 CH3
11a-44
11a-48
11a-50
11b-4
11b-15
11b-22
11b-26
11b-27 NO2
11b-38 CH3
11b-41
11b-44
11b-48
11b-50
CH3 96
H
H
H
H
H
H
H
H
H
99
97
95
91
88
>99
99
NO2
NO2
H
H
H
NO2
H
H
H
H
H
H
H
H
H
In summary, we have demonstrated that palladium-medi-
>99
ꢀ
CH3 98
ated, carbon carbon bond forming reactions are compatible
H
H
H
H
H
H
H
>99
99
99
93
>99
93
with the small molecule macroarray approach. As a test
case, a 100-member macroarray of unique stilbenes was con-
structed via spatially addressed Heck reactions in high con-
versions and purities. Subsequent biological testing of the
stilbene library (11a,b) in a bacterial QS assay revealed sev-
eral new and potent stilbene-derived inhibitors of a QS re-
ceptor in the Gram-negative bacterium, V. fischeri. Overall,
this work serves to highlight the emerging potential of the
small molecule macroarray platform for chemical biology
research. Ongoing work is directed at further extending the
scope of metal-mediated couplings on planar cellulose sup-
ports, as well as a thorough biological evaluation of the stil-
bene library, and will be reported in due course.
NO2
NO2
H
H
H
H
H
H
H
[a] Calculated by comparing initial styrene loadings and the quantity of
styrene remaining after the Heck reaction using UV calibration curves;
see the Supporting Information. [b] HPLC UV detection at 278 nm (for
stilbenes 11a) and 254 nm (for stilbenes 11b).
We next sought to evaluate the activity of the stilbene li-
brary (11a,b) as QS inhibitors, and performed a competitive
antagonism screen against the LuxR receptor in the bacteri-
al symbiont V. fischeri.[19] V. fischeri contains the canonical
QS system in Gram-negative bacteria based on LuxR-type
receptors, and thus represented an excellent model organism
for this initial study.[18,20] We utilized a V. fischeri mutant
strain that reported LuxR inhibition via luminescence, and
examined 5 mm stilbene against 5 mm of V. fischeriꢀs native
QS ligand, N-(3-oxo-hexanoyl)-l-homoserine lactone
(OHHL; Figure 2).
Experimental Section
Representative Heck reaction protocol on styrene-derivatized cellulose
support 8a,b: Spotting solutions were prepared by dissolving aryl iodides
(9, 0.25 mmol), PdACHTNUTRGENNUG(OAc)2 (50 mL of a 0.166m PdACHTUNTGERN(NUGN OAc)2 solution in
NMP), and Na2CO3 (31.8 mg, 0.30 mmol) in NMP (50 mL). Aliquots
(3.0 mL) of this solution were pipetted onto the 100 spots of styrene-func-
tionalized support 8a,b. The support was heated at 708C for 12 min on a
sand bath and then washed by immersion and swirling in 150 mL portions
Preliminary assays revealed five stilbenes (11a-10, 11a-12,
11a-20, 11a-37, and 11b-9) with inhibitory activities in the
2694
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 2692 – 2695