P. Lo Meo et al. / Tetrahedron 60 (2004) 9099–9111
9109
purified by chromatography on silica gel with light
petrol–ethyl acetate mixtures as eluents (yield 60–80%).
In some cases it was convenient to isolate the product
as the sodium salt: the product was dissolved in a
minimum amount of methanol and an equimolar amount
of a methanol concentrated NaOH solution was care-
fully added; the resulting solution was then dropped in a
ten-fold volume of Et2O, and the finely precipitated
product was filtered off.
4.1.11. N-(p-Nitro-phenyl)-1,3-diamino-propane (21).
Yellow crystals, mp 108–110 8C. IR (nujol) nmax 3358,
3298, 3275, 3229, 1603, 1549, 1504 cmK1 1H NMR
.
(250 MHz, DMSO-d6) d 1.48 (br s, 2H, –NH2), 1.68
(quint., JZ6.7 Hz, 2H, –CH2–CH2–CH2–), 2.58 (t, JZ
6.7 Hz, 2H, –CH2–NH2), 3.25 (br t, JZ6.7 Hz, 2H,
–NHCH2–), 6.68, 8.05 (2d, JZ9.2 Hz, 2HC2H, pNO2C6-
H4NH–), 7.39 (br s, 1H, –NH–). Anal. Calcd for
C9H13N3O2: C, 55.37; H, 6.71; N, 21.52. Found: C, 55.40;
H, 6.90; N, 21.29.
4.1.7. N-(p-Nitro-phenyl)-(D)-alanine sodium salt (17-
R$Na) and N-(p-Nitro-phenyl)-(L)-alanine sodium salt
(17-S$Na). Red-orange powder, 82–84 8C. IR (nujol) nmax
4.1.12. N-(p-Nitro-phenyl)-1,4-diamino-butane (22).
Yellow-orange crystals, mp 100 8C. IR (nujol) nmax 3352,
3269, 1611, 1580, 1547, 1501 cmK1. H NMR (250 MHz,
3294, 3216, 3167, 1600, 1550, 1500 cmK1 1H NMR
.
1
DMSO-d6) d 1.43 (d, JZ6.9 Hz, 3H, –CH3), 4.03–4.12 (m,
1H, –NHCH(CH3)–), 6.69, 8.02 (2d, JZ8.8 Hz, 2HC2H,
pNO2C6H4NH–), 7.42 (d, JZ7.2 Hz, 1H, –NH–). Anal.
Calcd for C9H9N2NaO4: C, 46.56; H, 3.91; N, 12.07. Found:
C, 46.42; H, 3.88; N, 11.91.
(250 MHz, DMSO-d6) d 1.36 (br s, 2H, –NH2), 1.40–1.52,
1.57–1.69 (2m, 2HC2H, –CH2–CH2–), 2.55–2.64 (m, 2H,
–CH2NH2), 3.15–3.22 (m, 2H, –NHCH2–), 6.68, 8.03 (2d,
JZ9.2 Hz, 2HC2H, pNO2C6H4NH–), 7.39 (bt, 1H, –NH–).
Anal. Calcd for C10H15N3O2: C, 57.40; H, 7.23; N, 20.08.
Found: C, 57.70; H, 7.49; N, 20.21.
4.1.8. N-(p-Nitro-phenyl)-sarcosine (18). Yellow solid, mp
120–140 8C (decomp.), IR (nujol) nmax 1740, 1599, 1583,
1518 cmK1. 1H NMR (250 MHz, DMSO-d6) d 3.16 (s, 3H,
pN–CH3), 4.35 (s, 2H, –CH2–), 6.82, 8.11 (2d, JZ9.4 Hz,
2HC2H, pNO2C6H4No), 12.95 (br s, 1H, –COOH). Anal.
Calcd for C9H10N2O4: C, 51.43; H, 4.80; N, 13.33. Found:
C, 51.72; H, 4.68; N, 13.41.
4.1.13. N-(p-Nitro-phenyl)-1,5-diamino-pentane hydro-
chloride (23$HCl). Yellow-orange powder, mp 161–
1
163 8C. IR (nujol) nmax 3321, 1603, 1528, 1501 cmK1. H
NMR (250 MHz, DMSO-d6) d 1.40–1.52 (m, 2H, –CH2–
CH2–CH2–CH2–CH2–), 1.57–1.73 (m, 2HC2H, –CH2–
CH2–CH2–CH2–CH2–), 2.77–2.86 (quint., JZ6.4 Hz, 2H,
–NHCH2–), 3.14 (br t, JZ6.4 Hz, 2H, –CH2NHC3 ), 3.50 (br
s, 3H, –NHC3 ), 6.71, 8.03 (2d, JZ9.3 Hz, 2HC2H, pNO2-
C6H4NH–), 7.53 (br s, 1H, –NH–). Anal. Calcd for
C11H18ClN3O2: C, 50.87; H, 6.99; N, 16.18. Found: C,
50.69; H, 7.08; N, 15.98.
4.1.9. N-(p-Nitro-phenyl)-(D)-proline (19-R). Orange-
brown solid; mp O250 8C (decomp.). IR (nujol) nmax
1
1720 cmK1. H NMR (250 MHz, DMSO) d 1.96–2.40 (m,
4H, –CH2–CH2CH2–CHo), 3.43–3.64 (m, 2H, pN–CH2–),
4.47 (dd, JZ8.6, 2.4 Hz, 1H, pCH–COOH), 6.63, 8.12 (d,
JZ9.3 Hz, 2H, pNO2C6H4No). Anal. Calcd for
C11H12N2O4: C, 55.93; H, 5.12; N, 11.86. Found: C,
55.77; H, 6.45; N, 11.40.
4.1.14. N-(p-Nitro-phenyl)-1,6-diamino-exane (24).
Yellow-orange crystals, mp 89–90 8C. IR (nujol) nmax
1
3225, 3178 1607, 1551, 1504 cmK1. H NMR (250 MHz,
DMSO-d6) d 1.36–1.45, 1.55–1.64 (2m, 6HC2H, –CH2–
CH2–CH2–CH2–), 1.87 (br s, 2H, –NH2), 2.54–2.57 (m, 2H,
–CH2NH2), 3.15–3.22 (m, 2H, –NHCH2–), 6.68, 8.03 (2d,
JZ9.3 Hz, 2HC2H, pNO2C6H4NH–), 7.36 (br t, 1H, –NH–).
Anal. Calcd for C12H19N3O2: C, 60.74; H 8.07; N 17.71.
Found: C, 60.57; H, 7.94; N, 17.81.
Diamine derivatives 20–25 were prepared as follows:
p-fluoro-nitrobenzene (10 mmol) was dissolved in DMSO
(20 mL) and 5 equiv of the appropriate diamine were added.
The mixture was allowed to react at 80 8C under stirring till
completion (TLC). The mixture was poured into water
(200 mL), acidified with HCl up to pHZ4 and extracted
with CH2Cl2. The aqueous phase was then treated with a
concentrated NaOH solution up to pHZ12 and extracted
with ethyl acetate. The organic extracts were dried on
anhydrous Na2SO4 and distilled in vacuo. The residue was
finally purified by crystallization from methanol (yield 75–
90%). Sometimes it was convenient to isolate the low-
melting product as hydrochloride: the product was dissolved
in a minimum amount of methanol and a slight excess of
12 M HCl was slowly added; the resulting solution was then
dropped in a ten-fold amount of Et2O and the product was
finally recovered by filtration.
4.1.15. N,N-Dimethyl-N0-(p-nitro-phenyl)-1,2-diamino-
ethane hydrochloride (25$HCl). Yellow powder, mp
178–180 8C. IR (nujol) nmax 3244, 2611, 2469, 1594,
1
1539, 11498 cmK1. H NMR (250 MHz, DMSO) d 2.85
(s, 6H, –NH(CH3)2C), 3.31 (2H, t, JZ6.6 Hz, –CH2-
NHCo), 3.62–3.70 (m, 2H, –NHCH2–), 6.81, 8.08 (2d,
JZ9.2 Hz, 2HC2H, pNO2C6H4NH–), 7.39 (br t, 1H, –NH–),
10.86 (br s, 1H, –NH(CH3)C2 ). Anal. Calcd for
C10H16ClN3O2: C, 48.88; H, 6.56; N, 17.10. Found: C,
48.69; H, 6.67; N, 16.95.
Stock phosphate buffer solutions were prepared according to
literature reports and used within a few days, after checking
the actual pH value. Freshly double-distilled water was used
for the preparation of the buffers, which were in turn used as
solvents for the preparation of the measurement solutions.
4.1.10. N-(p-Nitro-phenyl)-1,2-diamino-ethane (20).
Yellow solid, mp 138–141 8C. IR (nujol) nmax 3360, 3359,
1
3224, 3171, 1600, 1550, 1501 cmK1. H NMR (250 MHz,
DMSO-d6) d 1.68 (br s, 2H, NH2), 2.78 (t, JZ6.3 Hz, 2H,
–CH2NH2), 3.13–3.23 (m, 2H, –NHCH2–), 6.70, 8.04 (2d,
JZ9.3 Hz, 2HC2H, pNO2C6H4NH–), 7.36 (br t, 1H, –NH–).
Anal. Calcd for C8H11N3O2: C, 53.03; H, 6.12; N, 23.19.
Found: C: 52.81; H, 5.99; N, 23.31.
4.2. Measurement of pKa or pKCBH of 17–18 and 20–25
(i) A weighed amount (ca. 40 mmol) of the sodium salts of