LuxS Inhibitors
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 10 3009
HRESI-MS: m/z calcd for C35H52N2O8SNa+ (M + Na+) 683.3337,
found 683.3336.
2.78 (dd, J ) 14.4 Hz, 1.6 Hz, 1H), 2.72-2.59 (m, 2H), 2.09-
2.06 (m, 1H), 1.93-1.84 (m, 1H), 1.48 (s, 3H), 1.46 (s, 9H), 1.43
(s, 12H). 13C NMR (100 MHz, CDCl3): δ 171.3, 170.8, 155.3,
111.5, 82.1, 79.8, 79.0, 77.9, 53.4, 52.5, 34.4, 33.0, 28.7, 28.3, 28.0,
27.0, 25.8. HRESI-MS: m/z calcd for C21H37NO8SNa+ (M + Na+)
486.2132, found 486.2121.
(2S)-2-Amino-4-[(2R,3S)-2,3-dihydroxy-3-N-hydroxycarbam-
oylpropylmercapto]butyric Acid (10). A solution of 1 M BCl3 in
CH2Cl2 (0.50 mL, 0.50 mmol) was charged into a 10 mL round-
bottom flask and cooled to -78 °C, and compound 21 (53 mg,
0.080 mmol) in CH2Cl2 (0.72 mL) was added dropwise at -78 °C.
The yellow reaction mixture was stirred at -78 °C for 3 h. MeOH/
CH2Cl2 (2:1, 1.08 mL) was then added at -78 °C, and the mixture
was stirred for another 5 min. The solvent was removed by rotary
evaporation, and 2 mL of MeOH was added and then removed by
rotary evaporation. The residue was purified by silica gel chroma-
tography (30% H2O in CH3CN) to give product 4 as a white gel
(15 mg, 71% yield, Rf ) 0.34). The product was further purified
by affinity chromatography with Affi-Gel boronate gel (Bio-Rad),
which was eluted with 30 mM Na2HPO4-NaH2PO4 buffers of the
following pH values: 8.5, 8.1, 7.6, 7.0, 6.75, 6.5, 6.25, 6.0, 5.5,
5.0, and 4.5. Compound 4 was collected over the pH range of 6.5-
tert-Butyl (2S)-2-tert-Butoxycarbonylamino-4-{(4R,5R)-5-N-
hydroxycarbamoyl-2,2-dimethyl[1,3]dioxolan-4-ylmethylmer-
capto}butyrate (26). To a solution of ester 25 (63 mg, 0.14 mmol)
in MeOH (1 mL) cooled in icy water were added hydroxylamine
hydrochloride (40 mg, 0.55 mmol) and 85% KOH (40 mg, 0.61
mmol). This reaction mixture was stirred at rt for 36 h. The solvent
was removed under reduced pressure, and the white residue was
suspended in water. The aqueous mixture was carefully adjusted
to pH ≈ 5 with 1 N HCl and extracted with CHCl3 (3 × 10 mL).
The organic phase was concentrated and purified by silica gel
chromatography (1:1 EtOAc/hexanes) to produce 26 as a colorless
1
semisolid (44 mg, 70% yield, Rf ) 0.25). H NMR (400 MHz,
1
CDCl3): δ 9.22 (br s, 0.8H), 5.62 (br s, 0.2H), 5.18 (br m, 0.7H),
4.28-4.14 (m, 2H), 3.95 (br s, 0.3H), 3.22-3.04 (ABm, 1H), 2.80-
2.64 (ABm, 1H), 2.65-2.64 (m, 2H), 2.08-2.04 (m, 1H), 1.89-
1.88 (m, 1H), 1.46 (s, 12H), 1.44 (s, 12H). 13C NMR (100 MHz,
CDCl3): δ 171.4, 167.4, 155.5, 111.3, 82.2, 79.9, 79.5, 53.5, 34.2,
33.0, 28.7, 28.3, 28.0, 27.0, 26.0. HRESI-MS: m/z calcd for
C20H36N2O8SNa+ (M + Na+) 487.2085, found 487.2075.
6.0. H NMR (400 MHz, D2O): δ 4.09 (d, J ) 4.4 Hz, 1H), 3.86
(quintet, J ) 4.4 Hz, 1H), 3.68 (t, J ) 6.0 Hz, 1H), 2.65 (dd, J )
14.0 Hz, 4.0 Hz, 1H), 2.58-2.51 (m, 3H), 2.02-1.92 (m, 2H). 13
C
NMR (100 MHz, D2O): δ 174.2, 170.1, 72.8, 71.1, 53.9, 33.0,
30.3, 27.4. HRESI-MS: m/z calcd for C8H15N2O6S- (M - H-)
267.0651, found 267.0656.
Methyl (4R,5S)-5-Hydroymethyl-2,2-dimethyl[1,3]dioxolane-
4-carboxylate (23). To a solution of dimethyl (-)-2,3-O-isopro-
pylidene-L-tartrate (22) (0.95 mL, 5.0 mmol) in MeOH (25 mL)
was added 85% KOH pellet (0.33 g, 5.0 mmol). The solution was
stirred overnight at rt under an argon atmosphere. The solvent was
removed by rotary evaporation, and the residue was kept under
high vacuum for 3 h. The resultant white solid was mixed with
anhydrous THF (9.8 mL) and treated with 1 M BH3 in THF solution
(6.5 mL, 6.5 mmol) in an ice-water bath. The reaction mixture
was stirred for 8 h. Saturated NaHCO3 solution was slowly added
to the above mixture until bubbling stopped. The solvent was
removed by rotary evaporation, and the remaining aqueous phase
was extracted with EtOAc (100 mL). The organic phase was dried
over MgSO4 and concentrated. The residue was purified by silica
gel chromatography (1:1 EtOAc/hexanes) to provide 23 as a
(2S)-2-Amino-4-[(2R,3R)-2,3-dihydroxy-3-N-hydroxycarbam-
oylpropylmercapto]butyric Acid (11). Compound 26 (42 mg, 0.09
mmol) was dissolved in 1 mL of TFA, and the solution was stirred
at rt for 1 h. TFA was removed by rotary evaporation, and the
remaining residue was treated with 1 N HCl for 4 h at rt. The
mixture was concentrated, and the crude product was purified on
a silica gel column eluted with 30% H2O in CH3CN to produce a
1
white solid (24 mg, quantitative yield, Rf ) 0.34). H NMR (400
MHz, D2O): δ 4.25 (d, J ) 2.8 Hz, 1H), 4.02-3.98 (m, 1H), 3.79-
3.76 (m, 1H), 2.75-2.67 (m, 2H), 2.64 (t, J ) 7.6 Hz, 2H), 2.15-
2.00 (m, 2H). 13C NMR (100 MHz, D2O): δ 174.1, 170.9, 72.0,
70.6, 53.8, 33.6, 30.3, 27.2. HRESI-MS: m/z calcd for C8H15N2O6S-
(M - H+) 267.0651, found 267.0628.
D-Erythronohydroxamic Acid (12). This compound was syn-
1
colorless oil (0.34 g, 36% yield over two steps, Rf ) 0.29). H
thesized according to a literature procedure.31
NMR (400 MHz, CDCl3): δ 4.48 (d, J ) 7.6 Hz, 1H), 4.27-4.23
(m, 1H), 3.96 (dd, J ) 12.4 Hz, 3.2 Hz, 1H), 3.81 (s, 3H), 3.76
(dd, J ) 12.4 Hz, 3.2 Hz, 1H), 1.91 (br s, 0.8H), 1.50 (s, 3H), 1.48
(s, 3H).
(2S)-2-Amino-6-{2-[(5S)-5-amino-5-carboxypentylcarbamoyl-
methyldithio]acetylamino}hexanoic Acid (33). To a solution of
2-mercaptoacetic acid (14 µL, 0.20 mmol) in MeOH (0.5 mL) was
added H2O2 (20 µL, 0.18 mmol). The mixture was stirred for 1 h
at rt, and the solvent was evaporated. The white solid obtained was
kept under high vacuum for 6 h and mixed with l-NR-Boc-Lys-O-
tBu (61 mg, 0.20 mmol), followed by the addition of CH2Cl2 (1.5
mL), dicyclohexylcarbodiimide (42 mg, 0.21 mmol), and (dim-
ethylamino)pyridine (24 mg, 0.20 mmol). The reaction mixture was
stirred under argon for 18 h at rt. The mixture was filtered, and the
white precipitate was rinsed with EtOAc. The filtrate was pooled,
concentrated, and treated with TFA (0.8 mL) for 30 min. After
rotary evaporation of TFA, the residue was washed with CHCl3
and purified by silica gel chromatography (eluted with 30% H2O
in CH3CN) to afford 33 as a white solid (13 mg, 30% yield, Rf )
0.23). 1H NMR (400 MHz, D2O): δ 3.60 (t, J ) 6.4 Hz, 2H), 3.34
(s, 4H), 3.14 (t, J ) 6.8 Hz, 4H), 1.78-1.68 (m, 4H), 1.51-1.44
(m, 4H), 1.36-1.26 (m, 4H). 13C NMR (100 MHz, D2O): δ 174.8,
171.4, 54.7, 41.0, 39.5, 30.1, 28.0, 21.8. HRESI-MS: m/z calcd
for C16H30N4O6S2Na+ (M + Na+) 461.1504, found 461.1472.
(2S)-2-Amino-6-{3-[2-(5S)-5-amino-5-carboxypentylcarbamoyl-
ethyldithio]propionylamino}hexanoic Acid (34). This compound
was prepared in a manner similar to that of compound 33. 1H NMR
(400 MHz, D2O): δ 3.59 (t, J ) 6.0 Hz, 2H), 3.08 (t, J ) 6.8 Hz,
4H), 2.83 (t, J ) 6.8 Hz, 4H), 2.54 (t, J ) 6.8 Hz, 4H), 1.78-1.70
(m, 4H), 1.45-1.37 (m, 4H), 1.31-1.25 (m, 4H). 13C NMR (100
MHz, D2O): δ 174.7, 174.1, 54.7, 39.0, 35.0, 33.4, 30.1, 28.0, 27.1,
21.8. HRESI-MS: m/z calcd for C18H34N4O6S2Na+ (M + Na+)
489.1812, found 489.1801.
Methyl (4R,5R)-5-Bromomethyl-2,2-dimethyl[1,3]dioxolane-
4-carboxylate (24). To a solution of alcohol 23 (279 mg, 1.47
mmol) in CH2Cl2 (15 mL) were added triphenylphosphine (0.40 g,
1.53 mmol) and carbon tetrabromide (0.51 g, 1.53 mmol) in an
ice-water bath. The solution was stirred overnight at rt under argon.
The solvent was removed by rotary evaporation, and the residue
was purified by column chromatography (1:3 EtOAc/hexanes) to
give 24 as a colorless oil (0.23 g, 62% yield, Rf ) 0.47). 1H NMR
(250 MHz, CDCl3): δ 4.45-4.38 (m, 2H), 3.81 (s, 3H), 3.70-
3.64 (ABm, 1H), 3.60-3.54 (ABm, 1H), 1.52 (s, 3H), 1.46 (s, 3H).
Methyl (4R,5R)-5-[(3S)-3-tert-Butoxycarbonyl-3-tert-butoxy-
carbonylaminopropylsulfanylmethyl]-2,2-dimethyl[1,3]dioxolane-
4-carboxylate (25). Freshly prepared l-BocNHCH(CH2CH2SH)-
CO2tBu29 (142 mg, 0.48 mmol) was dissolved in dry DMF (2.5
mL), and the solution was purged with argon for 10 min and chilled
in an ice-water bath. A 1.5 M solution of LDA in cyclohexane
(0.6 mL, 0.9 mmol) was added, and the resulting solution was stirred
at 0 °C for 10 min, followed by the addition of bromide 24 (129
mg, 0.51 mmol) in DMF (1.5 mL). This reaction mixture was stirred
at rt for 2 days. The solvent was then removed by rotary
evaporation, and the yellow residue was suspended in saturated
NH4Cl solution and extracted with EtOAc (3 × 10 mL). The organic
layer was dried over MgSO4, concentrated, and purified by silica
gel chromatography (1:3 EtOAc/hexanes) to afford 25 as a colorless
1
semisolid (111 mg, 50% yield, Rf ) 0.32). H NMR (400 MHz,
CDCl3): δ 5.08 (br d, J ) 7.2 Hz, 0.8H), 4.37-4.32 (m, 2H), 4.25-
4.24 (m, 1H), 3.78 (s, 3H), 2.94 (dd, J ) 14.4 Hz, 3.6 Hz, 1H),
(2S)-2-Amino-6-{4-[3-(5S)-5-amino-5-carboxypentylcarbamoyl-
propyldithio]butyrylamino}hexanoic Acid (35). This compound