Reaction of naphthalene-2,3-dicarbaldehyde with cyanide; a unique oxidative condensation product

Article abstract of DOI:10.1002/jhet.5570420401

Naphthalene-2,3-dicarbaldehyde (NDA), a reagent used for the fluorescent detection of amino acids in the presence of cyanide, self-condenses in the presence of cyanide ion and methanol at room temperature to yield a unique crystalline product 2, 15-hydroxybenzo[g]benzo[6,7]isochromeno[4,3-c]isochromen- 7(15H)-one. The product is proposed to result from facile air oxidation of NDA to a methyl ester in combination with benzoin condensation. Product 2 does not to form in the absence of air. The gHMBC spectrum of 2 distinguishes it from a possible alternative isomeric condensation product.

Full text of DOI:10.1002/jhet.5570420401

May-Jun 2005
Reaction of Naphthalene-2,3-dicarbaldehyde with Cyanide;
A Unique Oxidative Condensation Product
475
Colin M. McGill, Kristian E. Swearingen, Kelly L. Drew, Brian T. Rasley,
*
and Thomas K. Green
Institute of Arctic Biology, Department of Chemistry & Biochemistry
University of Alaska Fairbanks, Fairbanks, Alaska 99775
fftkg@uaf.edu
Received February 2, 2004
Naphthalene-2,3-dicarbaldehyde (NDA), a reagent used for the fluorescent detection of amino acids in the
presence of cyanide, self-condenses in the presence of cyanide ion and methanol at room temperature to
yield a unique crystalline product 2, 15-hydroxybenzo[g]benzo[6,7]isochromeno[4,3-c]isochromen-7(15H)-
one. The product is proposed to result from facile air oxidation of NDA to a methyl ester in combination
with benzoin condensation. Product 2 does not to form in the absence of air. The gHMBC spectrum of 2 dis-
tinguishes it from a possible alternative isomeric condensation product.
J. Heterocyclic Chem., 42, 475 (2005).
Introduction.
tion of possible side products was made. We report here
the structural characterization of the condensation product,
2, 15-Hydroxybenzo[g]benzo-[6,7]isochromeno-[4,3-c]-
isochromen-7(15H)-one, that forms when NDA is reacted
with cyanide in the absence of amino acid, as shown in
Scheme 1. The product is isolated within 10 minutes reac-
tion time at room temperature as a yellow crystalline prod-
uct. It conveniently reacted to the full acetals 3a and 3b in
HCl and alcohol.
Naphthalene-2,3-dicarbaldehyde (NDA) 1 in the pres-
ence of cyanide was first introduced as a reagent for the
fluorescence detection of amino acids and peptides by
Carlson et al. in 1986 [1,2]. The reagent has been shown to
react rapidly with amino groups to form stable, highly flu-
orescent 2-substituted 1-cyanobenz[f]isoindoles as shown
below. Since that time, NDA has become a widely used
analytical reagent for amino acid and peptide analysis by
HPLC [3] and capillary electrophoresis [4].
NDA
isoindole
As initially reported, sodium cyanide is added to a
methanolic solution of NDA, immediately followed by an
aqueous solution of the amino acid [1]. The formation of a
pale yellow solution after addition of cyanide but prior to
addition of amino acid was reported, but no characteriza-
Structure Proof of 2.
The structure of 2 is supported by its IR spectrum, ele-
mental analysis, mass spectrum, and NMR spectra
1
13
including H, C, gCOSY (Figure 1), NOESY, gHSQC
(Figure 2), and gHMBC (8 Hz and 3 Hz, Figure 3-5)
Scheme 1
Condensation of NDA in the presence of air and cyanide in methanol.

476
C. M. McGill, K. E. Swearingen, K. L. Drew, B. T. Rasley, and T. K. Green
Vol. 42
1
spectra. Assignments of all H resonances and all but
relates with 7.65 in gCOSY. Therefore H-10 is 7.65 and
C-10 is 127.5. H-10 is coupled to 7.75 (gCOSY) so H-11
is 7.75 and C-11 is 130.1. H-11 is correlated to 8.20.
Therefore, H-12 is 8.20 and C-12 is 128.3. Irradiation of
8.36 singlet results in positive NOE at 8.20 so H-13 is 8.36
and C-13 is 119.9
13
two C resonances are made and are discussed below.
F2
(ppm)
NMR Assignments of C-H Groups on Right Side of
Molecule.
6.4
6.6
6.8
7.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
Irradiation of H-15 at 6.66 shows a positive NOE at
8.00. Therefore H-16 is 8.00 and C-16 is 125.3. H-5 must
be 8.15 and C-5 is 118.1. In the gHSQC, H-2 and H-3 are
at 7.55, which correlates to 126.7, and 7.58, which corre-
lates to 127.2.
Assignments of Quaternary Carbons of Left Side of
Molecule using gHMBC.
In Figure 3, H-8 shows 3-bond correlations with C-7
(C=O) carbon at 160.1, with C-9 at 129.8, with 12a and 13a
at 127.9 and 135.8. H-9 also shows a 3-bond correlation to
135.8. Therefore C-12a is 135.8 and C-13a is 127.9. C-9
also correlates to 132.5 (C-8) and 130.1, which must be C-
11. Besides C-12 at 128.3, H-13 correlates to 119.0 and a
broader peak at 131.5. The center of the peak at 131.5 has
no corresponding carbon, as shown in Figure 4, and is prob-
ably an overlap of 130.9 and 132.0. 119.0, 130.9, 132.0
correspond to C-7a, C-8a, C-13b. The HMBC spectrum (3
8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0 6.8 6.6
F1 (ppm)
Figure 1. gCOSY Spectrum of 2 in DMSO-d
6
F2
(ppm)
7.4
7.6
7.8
8.0
8.2
8.4
8.6
8.8
9.0
9.2
132
130
128
126
124
122
120
F1 (ppm)
Figure 2. gHSQC Spectrum of 2 in DMSO-d
6
NMR Assignments of C-H Groups on Left Side of
Molecule.
Hz, Figure 5) shows a clear correlation to 130.9 (apparent
de-emphasis of 132.0). H-12 also shows a correlation to
132.0 (shoulder) and therefore C-8a must be 132.0. H-12
correlates to 127.5, which must be C-10. The only carbons
Irradiation of H-8 at 8.96 shows a positive NOE at 8.25.
Therefore H-9 is 8.25 and C-9 is 128.8 (gHSQC). H-9 cor-

May-Jun 2005
Reaction of Naphthalene-2,3-dicarbaldehyde with Cyanide
477
F2
(ppm)
6.6
6.8
7.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
8.8
9.0
9.2
160
150
140
130
F1 (ppm)
120
110
100
Figure 3. gHMBC Spectrum of 2 in DMSO-d
6
F2
(ppm)
7.8
8.0
8.2
8.4
8.6
8.8
9.0
138
136
134
132
130
128
126
124
122
120
118
F1 (ppm)
Figure 4. Expanded gHMBC Spectrum (8 Hz) of 2 in DMSO-d
6
left unassigned on the left side are C-7a and C-13b, which
must be 119.0 and 130.9. The more downfield carbon at
130.9 is logically assigned to C-13b due to the oxygen
directly bonded to it. Additionally, the anomeric H-15 cor-
relates to 130.9, confirming it as C-13b.
H-15 correlates with 130.9 (C-13b), 125.2 (C-16), and
121.9, which must be C-5a. H-16 correlates with 93.1 (C-
15), 128.2 (C-1), 121.9 (C-5a) and 133.1, which must be C-
4a. H-5 correlates to what appears to a broad peak at 133.2,
which are probably two overlapping peaks. gHMBC (3 Hz,
Figure 3b) clearly shows the correlations of H-5 with 129.8
(apparent de-emphasis of adjacent peak). H-OH shows a
two-bond correlation to C-15 (93.1) but also a 3-bond corre-
Assignments of Quaternary Carbons of right side of
Molecule using gHMBC.

478
C. M. McGill, K. E. Swearingen, K. L. Drew, B. T. Rasley, and T. K. Green
Vol. 42
F2
(ppm)
7.6
7.7
7.8
7.9
8.0
8.1
8.2
8.3
8.4
8.5
8.6
136
134
132
130
128
126
124
122
120
F1 (ppm)
Figure 5. Expanded gHMBC Spectrum (3 Hz) of 2 in DMSO-d
6
lation to 129.8. Therefore C-15a must be 129.8. H-4 shows
only a single correlation to 126.7, which is a CH carbon that
must be C-2, assuming a 3-bond correlation. This leaves
127.2 as C-3. Finally, 132.7 and 133.8 remain unassigned
and must be C-5b and C-16a. Assignments are summarized
in Table 1 and Figure 4.
Table 1
1
13
NMR Correlations for 2 using H, C, NOE, gCOSY, gHSQC, gHMBC
O
9
8
7
10
11
7a
O
6
12a
13a
5b
5
4
1
12
13
13b
5a
4a
3
2
O
14
15a
16a
15
16
OH
C atoms separated by
One Bond Three Bonds
δ , ppm
H-#
J
gCOSY
δ
δ [a]
H
HH
c
c
8.96(s)
8.36(s)
8.25(d)
8.20(d)
8.15(s)
8.10(dd)
8.00(s)
7.98(dd)
7.91(d)
7.75(ddt)
7.65(dt)
7.58(dt)
7.55(dt)
6.66(d)
H-8
H-13
H-9
H-12
H-5
H-4
H-16
H-1
H-OH
H-11
H-10
H-3
--
--
132.4
119.9
129.8
128.3
118.1
128.4
125.3
128.2
129.8
130.1
127.5
127.2
126.7
93.1
127.9, 129.8, 135.8, 160.1
119.0, 128.3, (130.9,132.0)
130.1, 132.4
119.9, 127.5, 132.0(shoulder)
129.8 (gHMBC 3 Hz, Fig 3b)
126.7
8.3. 1.3
8.3, 1.3
--
8.3, 1.3
--
7.65
7.75
7.58
93.1, 121.9, 128.2, 133.1
127.3 (shoulder)
8.3, 1.3
6.9
7.55
6.66
1.3, 7.0, 8.3
1.3, 7.0, 8.3
1.3, 7.0, 8.3
1.3, 7.0, 8.3
6.9
7.65, 8.20
7.75, 8.25
7.55, 8.10
7.58, 7.98
7.91
135.8, 129.8
128.3, 132.0
133.1 (gHMBC 3 Hz, Fig 3b)
--
121.9, 125.2, 130.9
H-2
H-15
[a] All correlations are from gHMBC (8 Hz, Figure 3a) unless noted.

May-Jun 2005
Reaction of Naphthalene-2,3-dicarbaldehyde with Cyanide
479
We have no direct spectroscopic evidence for interme-
diate 1a; however, it is established that aromatic aldehy-
des oxidize to form methyl esters in methanol in the pres-
ence of manganese dioxide and cyanide [5,6]. This oxi-
dation was shown to proceed by oxidation of a cyanohy-
drin to an acyl cyanide, followed by methyl ester forma-
tion. One can envision a similar reaction here, except
with air as oxidizing agent, although it is surprising that
oxidation takes place so readily under such mild condi-
tions. Under identical reaction conditions, we found that
2-naphthaldehyde yields less than 5% methyl ester (NMR
yield) in 20 minutes, suggesting that only activated alde-
hydes, such as NDA, are efficiently air oxidized to
methyl esters in this time frame. In support of this idea,
we found that 4-acetylbenzaldehyde was quantitatively
reacted to methyl 4-acetylbenzoate in less than 20 min-
utes at room temperature.
Figure 6. Summary of NMR assignments of 2. Carbons 5b and 16a are
132.7 and 133.8 ppm.
Reaction Pathway.
The stoichiometry of the reaction demands that oxida-
tion of NDA takes place. The reaction conducted with
exclusion of air did not yield 2, but unidentified products,
demonstrating that formation of 2 requires the presence of
air. Thus we can propose a reaction pathway, shown in
Scheme 2, which involves (1) air oxidation of NDA to the
methyl ester 1a, catalyzed by cyanide, (2) benzoin conden-
sation to 1b, (3) cyclization to lactone 1c, (4) enolization to
1d, and finally (5) hemiacetal formation to 2. Steps 2-5
are reversible.
All of the steps in the proposed reaction Scheme 1 are
reversible except methyl ester formation. Thus 2' could
form from the alternative benzoin intermediate 1b' with a
similar reaction pathway as proposed for structure 2.
Scheme 2
Proposed Reaction Scheme for Formation of 2

480
C. M. McGill, K. E. Swearingen, K. L. Drew, B. T. Rasley, and T. K. Green
Vol. 42
13
13), 8.25 (d, 1H, 8.3 Hz, H-9), 8.20 (d, 1H, 8.3 Hz, H-12), 8.15 (s,
1H, H-5), 8.10 (dd, 8.3 Hz, 1.3 Hz, H-4), 8.00 (s, 1H, H-16), 7.98
(dd, 1H, 8.3 Hz, 1.3 Hz, H-1), 7.91 (d, 1H, 6.9 Hz, OH), 7.75 (ddt,
1H, 8.3 Hz, 7.0 Hz, 1.3 Hz, H-11), 7.65 (ddt, 8.3 Hz, 7.0 Hz, 1.3
Products 2 and 2' would be difficult to distinguish by
C
1
and H spectra alone according to ACD NMR predictive
software [7].
Hz, H-10), 7.58 (ddt, 1H, 8.3 Hz, 7.0 Hz, 1.3 Hz, H-3), 7.55 (ddt,
Proof of Structure 2 Versus 2'.
13
1H, 8.3 Hz, 7.0 Hz, 1.3 Hz, H-2), 6.66 (d, 1H, 6.9 Hz, H-15);
C
They can be distinguished by considering that H-13 at
8.36 ppm shows a 3-bond correlation with a C-13b at
130.9 (gHMBC, Figure 3). In addition, H-15 at 6.66 ppm
also correlates with C-13b. This is possible for structure 2,
as illustrated below. However, there is no carbon in 2' that
NMR (75 MHz, DMSO-d ): δ (ppm) 160.7 (C-7), 135.8 (C-12a),
6
133.8, 132.7 (C-5b,C-16a), 133.4 (C-4a), 133.1 (C-8), 132.4 (C-
8a), 130.9 (C-13b), 130.1 (C-11), 129.80 (C-9), 129.83 (C-15a),
128.5 (C-13a), 128.4 (C-4), 128.3 (C-12), 128.2 (C-1), 127.5 (C-
10), 127.2 (C-3), 126,7 (C-2), 125.3 (C-16), 121.9 (C-5a), 119.9
(C-13), 119.0 (C-7a), 118.1 (C-5), 93.1(C-15); gHMBC, gCOSY,
gHSQC, and NOESY spectra are available in the Supporting
Information; Mass Spectrometry; LRFAB (3-NBA) m/z 349.1
3
would show a J gHMBC correlation with both hydrogen
atoms. Thus 2' is excluded on the basis of gHMBC.
Additionally, AM1 calculations yield a heat of formation
of –46.3 kcal/mol for 2 and -30.9 (trans) and –26.8
kcal/mol (cis) for 2' so 2 is highly favored under equili-
brating conditions.
+
+
+
(M -OH), 366.1 (M ) (3-NBA/Li) 373.1 (M +Li).
Anal. Calcd. for C O : C, 78.7; H, 3.85; O,17.5.
H
24 14
4
Found: C, 78.9; H, 3.98; O 17.1.
15-Methoxybenzo[g]benzo[6,7]isochromeno[4,3-c]isochromen-
7(15H)-one (3a).
Compound 2 (8.0 mg, 0.022 mmol) was dissolved in 3 mL
methanol and 40 µL 6 N HCl was added. The reaction was
refluxed for 1 hour and cooled to 0 °C. The precipitate was cen-
trifuged, washed with cold water, dried and analyzed without fur-
1
ther purification, 90% mp 220-222 °C; H NMR (DMSO-d ): δ
6
(ppm) 9.02 (s, 1H, H-8), 8.52 (s, 1H, H-13), 8.29 (d, 1H, H-9),
8.26 (d, 1H, H-12), 8.23 (s, 1H, H-5), 8.16 (d,1H, H-4), 8.11 (s,
1H, H-16), 8.03 (d, 1H, H-1), 7.78 (dt, 1H, H-11), 7.70 (dt, 1H,
H-10), 7.63 (dt, 1H, H-3), 7.59 (dt, 1H, H-2), 6.54 (s, 1H, H-15),
3.64 (s, 3H, OCH ).
3
Anal. Calcd. for C H O C: 78.9; H, 4.24. Found: C, 79.1;
H, 4.21.
Conclusion.
25 16
4
NDA reacts with cyanide/methanol in the absence of
amino acid to yield an air-oxidized condensation product
2. The formation of 2 competes with formation of fluores-
cent isoindole in the NDA/cyanide/amino acid reaction in
methanol. We have noted formation of 2 as a minor prod-
15-Isopropoxybenzo[g]benzo[6,7]isochromeno[4,3-c]iso-
chromen-7(15H)-one (3b).
Compound 2 (5 mg, 0.014 mmol) was dissolved in 1 mL iso-
propanol and 3 drops of 6 N HCl was added. The reaction was
refluxed for 10 minutes and and cooled to 0 °C. The precipitate
was centrifuged, washed with cold water, dried and analyzed
1
uct by H NMR when reacting aspartic acid with
NDA/sodium cyanide in methanol. The key steps in for-
mation of 2 appear to be (1) facile cyanide-catalyzed air
oxidation of the NDA to either an acyl cyanide or methyl
ester and (2) benzoin condensation. Exclusion of air was
shown to avoid formation of 2.
1
without further purification, 85%, mp 208-210 °C; H NMR
(CDCl ): δ (ppm) 8.93 (s, 1H, H-8), 8.25 (s, 1H, H-13 or H-5),
3
8.23 (s, 1H, H-13 or H-5), 8.00 (d, 1H, H-9), 7.97 (d, 1H, H-12),
7.88 (d, 1H, H-4), 7.81 (d, 1H, H-1), 7.74 (s, 1H), 7.63 (dt, 1H,
H-11), 7.53 (dt, 1H, H-10), 7.48 (dt, 1H, H-3), 7.44 (dt, 1H, H-2),
6.41 (s, 1H, H-15).
Anal. Calcd. for C H O C: 79.4; H, 4.94. Found: C, 79.4;
H, 4.89.
27 20
4
EXPERIMENTAL
Acknowledgement.
Reaction of Naphthalene-2,3-dicarbaldehyde (NDA) (1) with
NaCN.
Mass spectrometry was provided by the Washington
University Mass Spectrometry Resource with support from the
NIH National Center for Research Resources (Grant No.
P41RR0954).
NDA (1) (35 mg, 0.22 mmol) was dissolved in 3.8 mL dry
methanol, then NaCN (12.3 mg, 0.25 mmol) was added and the
solution was reacted by shaking for 10 minutes. A yellow precip-
itate began to crystallize within 5 minutes. The solution was cooled
for 10 minutes in an ice bath and centrifuged and the supernatant
was removed. The precipitate was washed twice with cold water to
remove excess sodium cyanide. The product was dried under vac-
uum and identified as 6-hydroxybenzo[g]benzo-[5,6]indeno[1,2-
c]isochromen-14(6H)-one (2), 29.5% mp 287-289; IR (KBr):
REFERENCES AND NOTES
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(1987).
1
3439 (OH) 1725 (doublet, O-C=O) 1624, 1279, 1155; H NMR
(300 MHz, DMSO-d ): δ (ppm) 8.96 (s, 1H, H-8), 8.36 (s, 1H, H-
6

May-Jun 2005
Reaction of Naphthalene-2,3-dicarbaldehyde with Cyanide
481
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