Wang et al.
JOCArticle
6.5 Hz, 1H), 4.72 (d, J = 16.0 Hz, 1H), 4.69 (d, J = 16.0 Hz, 1H),
4.47 (ddd, J = 7.5, 6.5, 6.0 Hz, 1H), 4.31 (d, J = 4.5 Hz, 1H),
3.76 (d, J = 11.5 Hz, 1H), 3.39 (d, J = 11.5 Hz, 1H), 2.90 (t, J =
7.5 Hz, 2H), 2.56 (t, J = 7.5 Hz, 2H), 2.51 (dd, J = 14.0, 7.5 Hz,
1H), 2.46 (dd, J = 14.0, 6.0 Hz, 1H), 2.26 (m, 2H), 2.16 (m, 1H),
1.63 (m, 2H), 1.60 (s, 3H), 1.31-1.29 (m, 8H), 0.91-0.88
(m, 6H), 0.84 (d, J = 7.0 Hz, 3H); 1H NMR (500 MHz, CDCl3)
δ 7.87 (s, 1H), 7.55 (br s, 1H), 7.32 (d, J = 9.0, 1H), 5.67 (dt, J =
15.5, 7.0 Hz, 1H), 5.56 (dd, J = 15.5, 6.0 Hz, 1H), 4.79 (dd, J =
16.0, 6.0 Hz, 1H), 4.71 (dd, J = 16.0, 5.5 Hz, 1H), 4.51 (m, 1H),
4.47 (m, 1H), 3.79 (d, J = 11.5 Hz, 1H), 3.41 (d, J = 11.5 Hz,
1H), 2.87 (t, J = 7.5 Hz, 2H), 2.53 (t, J = 7.5 Hz, 2H), 2.50
(m, 1H), 2.45 (dd, J = 15.0, 8.5 Hz, 1H), 2.28 (m, 2H), 2.20 (m,
1H), 1.63 (dt, J = 14.0, 7.0 Hz, 2H), 1.59 (s, 3H), 1.30-1.25 (m,
8H), 0.92 (d, J = 7.0 Hz, 3H), 0.89-0.86 (m, 6H); 13C NMR
(125 MHz, CD3OD) δ 199.7, 175.0, 172.3, 169.9, 163.7, 148.1,
133.4, 128.9, 122.3, 84.8, 68.9, 43.5, 43.4, 40.9, 40.3, 32.0, 31.4,
31.0, 29.3, 28.6, 28.5, 27.7, 25.4, 23.6, 22.2, 18.5, 16.7, 13.0;
2924, 2853, 1735, 1689, 1450, 1272, 1168 cm-1; HRMS calcd for
C29H36O4S [M þ Na]þ 503.2232, found 503.2237.
Ester (32). A solution of 2,4,6-trichlorobenzoyl chloride
(1.9 μL, 12 μmol) and i-Pr2NEt (2.2 μL, 12 μmol) in THF
(120 μL) was added to acid 30 (7.2 mg, 12 μmol). The mixture
was stirred at 40 °C for 5 h before being concentrated under
vacuum. A solution of β-hydroxy-ester 31 (12.0 mg, 24.9 μmol)
in toluene (120 μL) was added to the residue followed by the
addition of DMAP (1.5 mg, 12 μmol). The mixture was stirred
for 16 h before a saturated aqueous solution of NH4Cl was
added. The mixture was extracted with ethyl acetate, the extract
was dried over Na2SO4, filtered, and concentrated. The residue
was purified by silica gel column chromatography (hexanes-
ethyl acetate, 4:1 to 3:2) to give 32 (11.0 mg, 10.6 μmol, 85%) as
mixture of C2-epimers (2R:2S = 1.5:1): HRMS calcd for
C58H64N4O8S3 [M þ Na]þ 1063.3784, found 1063.3789.
Largazole (1) and 2-epi-Largazole (33). To a rt solution of 32
(7.0 mg, 6.7 μmol) in CH2Cl2 (0.5 mL), was added diethylamine
(0.25 mL). After stirring for 3 h, the volatiles were removed
under vacuum, and the residue was redissolved in CH2Cl2
(0.5 mL) and i-Pr2NEt (0.1 mL). After the resulting solution
stirred for 10 min, the solvent was removed under vacuum, and
the residue was azotropically dried twice with toluene (2 ꢀ
2 mL). The residue was dissolved in CH3CN (7 mL), and
2-(1H-7-azabenzotriazole-1-yl)-1,1,3,3-tetramethyl uronium hexa-
fluorophosphate (HATU, 5.1 mg, 13 μmol), 1- hydroxy-7-
azabenzotriazole (HOAt, 1.8 mg, 13 μmol), and i-Pr2NEt
(4.6 μL, 27 μmol) were added. The resulting solution was stirred
for 12 h before being concentrated under vacuum. The residue
was purified by silica gel column chromatography to give a
mixture of 1 and 33 (3.0 mg, 4.8 μmol, 72%). This mixture was
separated by preparative TLC (hexanes-ethyl acetate-methanol,
10:10:1) to give 1 (1.2 mg, 1.9 μmol) and 33 (1.8 mg, 2.9 μmol) as
[R]22 -24 (c 0.16, MeOH); IR (neat) 3381, 3082, 2957, 2927,
D
2856, 1671, 1652, 1606, 1538, 1514, 1461, 1408, 1184, 1045 cm-1
;
HRMS calcd for C29H44N4O6S3 [M þ Na]þ 663.2315, found
663.2322.
Fmoc-Amino Acid (30). Thiazoline 5 (18.3 mg, 35.7 μmol) was
dissolved in CH2Cl2/TFA (1:1 v/v, 2 mL) and stirred at rt for 2 h.
The solvent was removed, and the residue was dried under high
vacuum for 1 h. Saturated aqueous NaHCO3 (0.4 mL) was
added followed by 9-fluorenylmethyl chloroformate (FmocCl,
9.2 mg, 0.43 mmol) in 1,4-dioxane (0.4 mL). After vigorous
stirring for 1 h, 1 M aqueous KHSO4 was added until pH 2 was
attained. The mixture was then extracted with ethyl acetate, and
the combined extracts were dried over Na2SO4, filtered, and
concentrated. The residue was purified by silica gel column
chromatography (chloroform-methanol, 1:0 to 20:1) to yield
30 (19.8 mg, 34.3 μmol, 96%) as a colorless oil: Rf 0.14 (HPTLC,
CHCl3-MeOH, 10:1);1H NMR (500 MHz, CD3OD) δ 8.18 (s,
1H), 8.02 (br t, J = 5.5 Hz, 1H), 7.81 (d, J = 7.5 Hz, 2H), 7.67 (d,
J = 7.5 Hz, 2H), 7.62 (d, J = 8.5 Hz, 2H), 7.40 (t, J = 7.5 Hz,
2H), 7.31 (d, J = 7.5 Hz, 2H), 4.60 (s, 2H), 4.45 (d, J = 6.5 Hz,
2H), 4.38 (m, 1H), 4.24 (t, J = 6.5 Hz, 1H), 3.78 (d, J = 11.5 Hz,
1H), 3.39 (d, J = 11.5 Hz, 1H), 2.11 (m, 1H), 1.61 (s, 3H), 0.92
(d, J = 7.0 Hz, 3H), 0.88 (d, J = 7.0 Hz, 3H); 13C NMR
(125 MHz, CD3OD) δ 175.4, 175.4, 172.9, 172.9, 171.7, 163.8,
157.4, 148.3, 143.8, 141.3, 127.4, 126.8, 124.8, 122.3, 119.6, 84.7,
66.7, 57.4, 57.3, 48.5, 30.5, 23.6, 18.2, 16.7; [R]22D -36.1 (c 0.90,
MeOH); IR (neat) 3385, 2967, 1726, 1661, 1520, 1450, 1252,
1194, 1143, 1041 cm-1; HRMS calcd for C29H30N4O5S2 [M þ
Na]þ 601.1555, found 601.1562.
1
colorless oils. Analytical data for largazole (1): H NMR (500
MHz) δ 7.76 (s, 1H), 7.18 (d, J = 9.5 Hz, 1H), 6.44 (dd, J = 9.5,
3.0 Hz, 1H), 5.83 (dt, J = 15.5, 6.5 Hz, 1H), 5.67 (app t, J = 7.0
Hz, 1H), 5.53 (dd, J = 16.0, 7.0 Hz, 1H), 5.30 (dd, J = 17.5, 9.5
Hz, 1H), 4.62 (dd, J = 9.5, 3.5 Hz, 1H), 4.29 (dd, J = 17.5, 3.0
Hz, 1H), 4.06 (d, J = 11.5 Hz, 1H), 3.29 (d, J = 11.5 Hz, 1H),
2.91 (t, J = 7.0 Hz, 2H), 2.86 (dd, J = 16.5, 10.0 Hz, 1H), 2.70
(dd, J = 16.0, 2.5 Hz, 1H), 2.53 (t, J = 7.5 Hz, 2H), 2.32 (br q,
J = 7.5 Hz, 2H), 2.11 (m, 1H), 1.87 (s, 3H), 1.65 (m, 2H),
1.29-1.27 (m, 8H), 0.88 (m, 3H), 0.70 (d, J = 6.5 Hz, 3H), 0.53
(d, J = 6.5 Hz, 3H); 13C NMR (125 MHz) δ 199.4, 173.6, 169.4,
168.9, 167.9, 164.6, 147.5, 132.7, 128.4, 124.2, 84.5, 72.0, 57.8,
44.2, 43.4, 41.1, 40.5, 34.2, 32.3, 31.6, 28.9, 28.9, 27.9, 25.7, 24.2,
22.6, 18.9, 16.7, 14.1; [R]22D þ21 (c 0.10, MeOH); IR (neat) 3370,
β-Hydroxy-fluorenylmethanol Ester (31). To a suspension of
thiazolium salt 27 (49 mg, 0.21 mmol) in CH2Cl2 (0.2 mL) was
added i-Pr2NEt (71 μL, 0.21 mmol). The mixture was agitated
manually for 1 min and then added to a solution of aldehyde 4
(58 mg, 21 mmol) and 9-fluorenylmethanol (159 mg, 810 μmol)
in CH2Cl2 (0.5 mL). The mixture was stirred for 30 min before
saturated aqueous NH4Cl was added. The mixture was ex-
tracted with diethyl ether, and the combined extracts were dried
over MgSO4, filtered, and concentrated. The residue was pur-
ified by silica gel column chromatography (hexanes-ethyl
acetate, 9:1) to give 31 (76 mg, 0.16 mmol, 77%) as pale yellow
oil: Rf 0.29 (hexanes-ethyl acetate, 4:1); 1H NMR (500 MHz) δ
7.81 (d, J = 7.5 Hz, 2H), 7.62 (d, J = 7.5 Hz, 2H), 7.42 (m, 2H),
7.34 (m, 2H), 5.71 (dt, J = 15.5, 6.5 Hz, 1H), 5.54 (dd, J = 15.5,
6.5 Hz, 2H), 4.47 (m, 3H), 4.14 (t, J = 6.0 Hz, 1H), 2.92 (t, J =
7.5 Hz, 2H), 2.61 (d, J = 1.5 Hz, 1H), 2.59 (d, J = 9.0 Hz, 1H),
2.55 (t, J = 7.5 Hz, 2H), 2.31 (q, J = 7.0 Hz, 2H), 1.67 (m, 2H),
1.33-1.19 (m, 8H), 0.89 (m, 3H); 13C NMR (125 MHz) δ 199.5,
172.0, 143.7, 143.6, 141.3, 132.7, 129.7, 127.9, 127.2, 125.0,
120.1, 68.5, 66.5, 46.8, 44.2, 41.6, 32.2, 31.6, 29.7, 28.9, 28.2,
3085, 2926, 2854, 1738, 1682, 1552, 1504, 1259, 1100, 1029 cm-1
;
HRMS calcd for C29H42N4O5S3 [M þ Na]þ 645.2210, found
645.2201. Analytical data for 2-epi-largazole (33): 1H NMR (500
MHz) δ 7.68 (s, 1H), 7.21 (d, J = 8.0 Hz, 1H), 6.37 (dd, J = 7.5,
5.0 Hz, 1H), 5.89 (dt, J = 15.5, 6.5 Hz, 1H), 5.80 (app t, J =
9.0 Hz, 1H), 5.43 (dd, J = 15.5, 8.5 Hz, 1H), 5.08 (d, J = 17.0,
8.0 Hz, 1H), 4.28 (d, J = 11.0 Hz, 1H), 4.28 (dd, J = 17.0, 2.0 Hz,
1H), 4.23 (dd, J = 16.5, 5.0 Hz, 1H), 3.20 (d, J = 11.0 Hz, 1H),
2.88 (dt, J = 7.5, 2.0 Hz, 2H), 2.82 (dd, J = 16.5, 10.5 Hz, 1H),
2.58 (d, J = 16.5 Hz, 1H), 2.53 (t, J = 7.5 Hz, 2H), 2.29 (br q,
J = 7.0 Hz, 2H), 2.13 (m, 1H), 1.80 (s, 3H), 1.64 (m, 2H),
1.30-1.23 (m, 8H), 0.97 (d, J = 7.0 Hz, 3H), 0.89 (d, J = 6.5 Hz,
3H), 0.88 (m, 3H); 13C NMR (125 MHz) δ 199.4, 173.6, 169.4,
167.7, 167.6, 162.2, 147.7, 134.6, 128.5, 124.2, 85.0, 72.5, 59.7,
44.2, 41.6, 40.8, 40.3, 32.2, 32.2, 31.6, 28.9, 28.9, 27.8, 26.6, 25.6,
22.6, 18.8, 18.0, 14.1; [R]22D þ43 (c 0.16, CDCl3); IR (neat) 3342,
3076, 2925, 2857, 1738, 1682, 1552, 1503, 1259, 1107, 1034 cm-1
;
HRMS calcd for C29H42N4O5S3 [M þ Na]þ 645.2210, found
645.2201.
Materials and Methods for Biological Assays. The MTT assay
for cell viability was performed according to previous reported
25.7, 22.6, 14.1; [R]22 -3.49 (c 1.58, CHCl3); IR (neat) 3461,
D
J. Org. Chem. Vol. 76, No. 4, 2011 1149