BINOL-Amino Acid Conjugates
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 26 6577
6.56 (broad s, 2 H), 6.68 (broad s, 2 H), 7.10 (broad s, 2 H), 7.77
(broad s, 2 H), 7.96 (broad s, 2 H). 1H NMR (DMSO-d6) δ:
1.95–2.11 (m, 6 H), 2.43–2.51 (m, 2 H), 3.38–3.41 (m, 2 H),
3.62–3.75 (m, 2 H), 4.47–4.52 (m, 2 H), 4.56–4.79 (m, 4 H),
6.93–7.01 (m, 2 H), 7.21–7.30 (m, 2 H), 7.32–7.38 (m, 2 H), 7.92
(dd, 2 H, J ) 4.0, J ) 7.8 Hz), 8.14 (d, 2 H, J ) 7.5 Hz). 13C
NMR (D2O) δ: 22.54 (CH2), 28.42 (CH2), 54.80 (CH2), 55.07
(CH2), 67.06 (CH), 113.23 (C), 119.33 (C), 123.47 (CH), 124.34
(CH), 128.08 (C), 128.12 (CH), 128.66 (CH), 134.03 (CH), 134.34
(C), 151.13 (C), 171.85 (C). Anal. Calcd (C32H34Cl2N2O6): C, H,
Cl, N.
neration of related transient electrophiles has been achieved in
excellent quantum yields using BINOL-amino acid and -amino
ester derivatives as the precursors. QM-trapping experiments
show that bis-alkylation is the result of the sequential generation
of two monoalkylating BINOL-QMs. The majority of the
BINOL-amino acid and -amino ester precursors, when pho-
toactivated at 360 nm in the presence of supercoiled plasmid
DNA (pBR322), displayed DNA cross-linking potency com-
parable to that of the quaternary ammonium salts (range of 1–5
µM). Unlike the latter, the amino acid methyl esters exhibit
potent photocytotoxicity against the human colorectal adeno-
carcinoma LoVo cell line in the nanomolar concentration range
(130–230 nM). Among the 3,3′-CH2Y-disubstituted BINOLs
tested, the L-proline methyl ester congener stands out as the
most promising lead because, contrary to other derivatives, it
showed remarkably high photoselectivity, displaying prominent
cell killing effects only after UV irradiation. In this connection,
it is worth recalling that PS, one of the most effective phototoxic
agents thus far reported, is about 4 times less potent than our
newly tested compounds. In addition, we have shown that
BINOLAMs efficiently reach their DNA target inside the cells.
However, their mechanism of action differs to some extent from
that of a photoactivable reference drug, such as PS. In fact, we
have displayed that the photogenerated QMs inside the cells
exhibit mono- and bis-alkylating properties, resulting in DNA
scission and cross-linking. Analysis of DNA sequence specificity
and alkylation product characterization represent the next step
toward the development of potent photocytotoxic-selective
compounds.
(R,S,S)-6·2HCl. White crystals. mp > 177 °C (dec.). 1H NMR
(D2O) δ: 1.82 (broad s, 2 H), 2.05 (broad s, 4 H), 2.44 (broad s, 2
H), 3.25 (broad s, 2 H), 3.62 (broad s, 2 H), 4.17 (broad s, 2 H),
4.42 (d, 2 H, J ) 11.3 Hz), 4.58 (d, 2 H, J )11.3), 6.59 (broad s,
2 H), 6.70 (broad s, 2 H), 7.12 (broad s, 2 H), 7.80 (broad s, 2 H),
8.01 (broad s, 2 H). 13C NMR (D2O) δ: 22.60 (CH2), 28.55 (CH2),
54.81 (CH2), 55.17 (CH2), 67.12 (CH), 113.33 (C), 119.37 (C),
123.57 (CH), 124.37 (CH), 128.00 (C), 128.22 (CH), 128.69 (CH),
134.06 (CH), 134.39 (C), 151.17 (C), 171.89 (C). Anal. Calcd
(C32H34Cl2N2O6): C, H, Cl, N.
7. Equimolar diastereomeric mixture. Yellow oil. 1H NMR
(CDCl3) δ: 1.25–1.45 (s, 6 H), 3.25–3.75 (m, 2 H), 3.8 (s, 6 H),
4.00–4.15 (m, 2 H), 4.25–4.45 (m, 2 H), 7.10–7.35 (m, 6 H),
7.70–7.90 (m, 4 H). 13C NMR (CDCl3) δ: 18.84 (CH3), 51.31
(CH2), 52.10 (CH), 55.40 (CH3), 123.06 (CH), 124.7(CH), 126.1
(CH), 127.7 (CH), 127.9 (CH), 133.65 (C), 153.18 (C), 174.77 (C).
Anal. Calcd (C30H32N2O6): C, H, N.
8. Equimolar diastereomeric mixture. Yellow oil. 1H NMR
(CDCl3) δ: 1.25–1.45 (s, 12 H), 3.10–3.25 (m, 2 H), 3.65–3.80
(m, 2 H), 3.85 (s, 6 H), 3.90–4.35 (m, 4 H), 7.10–7.35 (m, 6 H),
7.70–7.90 (m, 4 H). 13C NMR (CDCl3) δ: 18.97 (CH3), 51.81
(CH2), 51.93 (CH), 60.31 (CH3), 123.06 (CH), 124.7(CH), 126.1
(CH), 127.7 (CH), 127.9 (CH), 133.45 (C), 154.08 (C), 174.13 (C).
Anal. Calcd (C34H40N2O6): C, H, N.
Experimental Section
General Procedures. The BINOLs 2b and 3b,7b,26 the dialde-
hyde 11,20,28 and the dibromide 1229 have been synthesized
according to published procedures. The diastereomerically pure
(S,S,S)- and (R,S,S) BINOL-esters 4 and 5 have been previously
synthesized and characterized.7c The alkylation adducts 13 and 14
were purified and characterized by a comparison to authentic
samples.7b
General Reductive Amination for the Synthesis of 4, 5,
and 7–9. The followed procedure is a modified version that is
already published.19 A suspension of L-amino-ester HCl (5 mmol)
in CH2Cl2 (25 mL) was added to a CH2Cl2 solution of Et3N (1
mL). The solution was stirred at room temperature for 1 h, and
then a solution of dialdehyde 11 (700 mg, 2 mmol) in CH2Cl2 was
added together with molecular sieves at 4 Å. This solution was
stirred under nitrogen atmosphere, at room temperature. After 16 h,
NaBH(OAc)3 (880 mg, 4 mmol) was added. The resulting suspen-
sion was further stirred for another 3 h at room temperature, under
an inert atmosphere. At this time, a solution of Na2CO3 was added
to the mixture, then the organic layer was separated, and the residual
solution was extract twice with CH2Cl2.
The mixture of the reaction has been separated by silica-gel
column chromatography, eluting with 7:3 cyclohexane/ethylacetate.
Synthesis of 6 and 10 by Deprotection of 4 and 9: General
Procedure.21 The t-butyl amino ester (1 mmol) was deprotected
by dissolving it in a solution of trifluoroacetic acid (1.94 mL, 13
mmol) and dichloromethane (10 mL) in the presence of triethyl-
silane (0.8 mL, 2.5 mmol), at room temperature. After stirring for
25 min, 1 M HCl (1 mL) was added and the solvent was removed
in vacuo. The residue was suspended in diethyl ether, and the
product was isolated by filtration. The yields were almost quantita-
tive (93%), only using triethylsilane as the carbocation scavenger.
3,3′-Bis-(2-carboxypyrrolidin-1-ylmetil)-1,1′-dinaphtyl-2,2′-
diolo·2HCl (6). (S,S,S)-6 2HCl. White crystals. mp > 180 °C
(dec.). 1H NMR (D2O) δ: 1.85 (broad s, 2 H), 2.01 (broad s, 4 H),
2.41 (broad s, 2 H), 3.25 (broad s, 2 H), 3.59 (broad s, 2 H), 4.18
(broad s, 2 H), 4.40 (d, 2 H, J ) 11.3 Hz), 4.55 (d, 2 H, J )11.3),
9. The compound was not characterized by NMR and used for
the further step in the synthesis of 10.
10. Equimolar diastereomeric mixture. Yellow oil. 1H NMR
(D2O) δ: 1.30–2.10 (m, 12 H), 2.60–3.10 (m, 4 H), 3.75–3.95 (m,
2 H), 4.25–4.65 (m, 4 H), 6.90–7.00 (m, 2 H), 7.20–7.40 (m, 4 H),
7.80–8.15 (m, 4 H). 13C NMR (D2O) δ: 21.49 (CH2), 24.80 (CH2),
26.25 (CH2), 28.73 (CH2), 28.89 (CH2), 29.19 (CH2), 38.92 (CH2),
46.52 (CH2), 47.02 (CH2), 47.47 (CH2), 48.81 (CH), 52.74 (CH),
113.62 (C), 113.69 (C), 123.75 (CH), 123.81 (CH), 124.59 (CH),
128.3 (CH), 128.45 (C), 128.66 (C), 128.71 (CH), 133.0 (CH), 133.5
(CH), 133.6 (CH), 134.35 (C), 134.5 (C), 151.16 (C), 151.30 (C),
171.79 (C), 171.89 (C). Anal. Calcd (C34H44Cl2N4O6): C, H,
Cl, N.
1
(S,S)-15·HCl. Yellow oil. H NMR (D2O) δ: 1.55–1.75 (m, 2
H), 2.15–2.22 (m, 1 H), 2.28–2.45 (m, 1 H), 2.48–2.60 (m, 1 H),
3.15–3.25 (m, 1 H), 3.65–3.80 (m, 1 H), 3.85 (d, 1 H, J ) 13.2),
4.60 (d, 1 H, J ) 13.2), 5.60 (m, 2 H), 5.70 (m, 1 H, acid),
7.20–7.30 (m, 4 H), 7.30–7.40 (m, 2 H), 7.55–7.70 (m, 4 H), 8.50
(s, 2 H, acid). 13C NMR (C5D5N) δ: 23.39 (CH2), 29.93 (CH2),
53.14 (CH2), 57.27 (CH2), 61.39 (CH2), 66.25 (CH), 116.09 (C),
116.34 (C), 125.44 (CH), 125.84 (CH), 126.27 (CH), 126.43 (CH),
126.48 (CH), 126.61 (CH), 128.32 (CH), 128.89 (CH), 128.96 (CH),
129.26 (CH), 133.05 (C), 134.41 (C), 153.07 (C), 155.23 (C),
176.15 (C). Anal. Calcd (C27H26ClNO5): C, H, Cl, N.
(R,S)-15·HCl. Yellow oil. 1H NMR (C5D5N) δ: 1.60–1.80 (m,
2 H), 2.05–2.20 (m, 1 H), 2.25–2.40 (m, 1 H), 2.48–2.60 (m, 1 H),
3.00–3.15 (m, 1 H), 3.65–3.80 (m, 1 H), 3.90 (d, 1 H, J ) 13.2),
4.82 (d, 1 H, J ) 13.2), 5.62 (m, 2 H), 5.70 (m, 1 H, acid),
7.20–7.30 (m, 4 H), 7.30–7.40 (m, 2 H), 7.55–7.70 (m, 4 H), 8.50
(s, 2 H, acid). 13C NMR (C5D5N) δ: 23.39 (CH2), 29.93 (CH2),
53.14 (CH2), 57.27 (CH2), 61.39 (CH2), 66.25 (CH), 116.09 (C),
116.34 (C), 125.44 (CH), 125.84 (CH), 126.27 (CH), 126.43 (CH),
126.48 (CH), 126.61 (CH), 128.32 (CH), 128.89 (CH), 128.96 (CH),
129.26 (CH), 133.05 (C), 134.41 (C), 153.07 (C), 155.23 (C),
176.15 (C). Anal. Calcd (C27H26ClNO5): C, H, Cl, N.