Synthesis of schaefferals A and B, unusual phenylhydrazine derivatives from mushrooms of the genus agaricus

Article abstract of DOI:10.1055/s-0029-1218790

Schaefferals were identified as chromogens responsible for the development of an orange to red color after treating the caps of certain Agaricus species with aniline and nitric acid (Schaeffers cross reaction). The structures of schaefferals A and B were confirmed by total synthesis. The color reaction can be explained by reaction of their aldehyde group with aniline and protonation of the azomethine thus formed, yielding a red delocalized cation. Georg Thieme Verlag Stuttgart - New York.

Full text of DOI:10.1055/s-0029-1218790

PAPER
2287
Synthesis of Schaefferals A and B, Unusual Phenylhydrazine Derivatives from
Mushrooms of the Genus Agaricus
S
ynthesisof Scha
e
e
fferals ngin Kileci-Ksoll,b Christian Winklhofer,a Wolfgang Steglich*a
a
Department Chemie und Biochemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5–13, 81377 München, Germany
Fax +49(89)218077756; E-mail: wos@cup.uni-muenchen.de
b
Kekulé-Institut für Organische Chemie und Biochemie der Universität Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
Received 16 April 2010
Dedicated to Professor Rolf Huisgen on the occasion of his 90th birthday
confirm the structures of the chromogens 1a and 1b, their
total synthesis was carried out.
Abstract: Schaefferals were identified as chromogens responsible
for the development of an orange to red color after treating the caps
of certain Agaricus species with aniline and nitric acid (Schaeffer’s
cross reaction). The structures of schaefferals A and B were con-
firmed by total synthesis. The color reaction can be explained by re-
action of their aldehyde group with aniline and protonation of the
azomethine thus formed, yielding a red delocalized cation.
The synthesis commenced with 4-aminobenzylamine (2),
which on treatment with methyl trifluoroacetate furnished
amine 3 in 96% yield by selective acylation of the aliphat-
ic amino group (Scheme 1). Diazotization of 3 followed
by reduction of the resulting diazonium salt with tin(II)
chloride gave the phenylhydrazine derivative 4 in 54%
yield, which on condensation with aromatic aldehydes af-
forded the hydrazones 5. After removal of the trifluoro-
acetyl group with aqueous barium hydroxide, the primary
amines 6 were transaminated with isonicotinaldehyde and
1,8-diazabicyclo[5.4.0]undec-7-ene3 to afford schaeffer-
als A (1a) and B (1b) in 55% and 33% yield, respectively.4
Using the same sequence, the corresponding nitro ana-
logue 1d was also prepared.
Key words: schaefferals, 4-hydrazinobenzaldehyde derivatives,
Agaricus, Schaeffer reaction
In 1933 the mycologist Julius Schäffer1 discovered that on
drawing crosswise lines of aniline and nitric acid on the
caps of certain Agaricus species, a fire-orange color
developed at the crossing point. The test, known as
Schaeffer’s cross reaction, is of value for the taxonomy of
the genus Agaricus and characteristic for species of the
section Flavescentes. Since the chemical basis of this re-
markable color reaction was still unknown, we set out to
study it in more detail.
CH2NH2
CH2NHCOCF3
b
CH2NHCOCF3
c
a
We were able to isolate three Schaeffer-active com-
pounds, named schaefferals A, B, and C, in amounts of
about 10 mg per kg fresh weight from the methanol ex-
tract of the edible mushrooms Agaricus silvicola (Vitt.)
Sacc. (German: Anis-Egerling) and A. arvensis Schff. ex
Fr. (German: Schaf-Champignon).2 From their spectro-
scopic properties, structures 1a and 1b could be proposed
for schaefferals A and B, respectively (Figure 1). Schaef-
feral C possesses the same general structure; however, the
nature of the substituent R remains unknown. In order to
NH2
NH2
HNNH2 ⋅ HCl
2
3
4
CH2NHCOCF3
CH2NH2
e
d
1
NH
H
NH
H
N
N
R
R
6
5
7
6
3
5'
6'
CHO
H
N
a R = H
b R = OH
d R = NO2
5
7'
1
2
R
4'
1'
N
4
H
3'
2'
Scheme 1 Reagents and conditions: F3CCO2Me, MeOH, r.t., 1 h,
96%; (b) NaNO2, HCl, –5 °C, 30 min, then SnCl2·2 H2O, 0 °C, 54%;
(c) 4-RC6H4CHO, acetate buffer pH 5, overnight 68% (5a), 60% (5b),
94% (5d); (d) Ba(OH)2, aq MeOH, r.t., 65% (6a), 71% (6b), 89%
(6d); (e) isonicotinaldehyde, DBU, DMF, r.t., overnight, then aq
KHSO4, 55% (1a), 33% (1b), 36% (1d).
1a, R = H, schaefferal A
1b, R = OH, schaefferal B
1c, R = X (unknown), schaefferal C
1d, R = NO2, nitro analogue
Figure 1 Schaeffer chromogens from Agaricus sp. and a synthetic
nitro analogue
All three synthetic compounds exhibited the Schaeffer re-
action, which was performed by spraying the TLC spots
on silica gel plates with aniline (yellow color) and subse-
quently with a mineral acid (orange-red color).5 The for-
SYNTHESIS 2010, No. 13, pp 2287–2291
Advanced online publication: 20.05.2010
DOI: 10.1055/s-0029-1218790; Art ID: C01810SS
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x
.
2
0
1
0

2288
R. Kileci-Ksoll et al.
PAPER
N-(4-Aminobenzyl)-2,2,2-trifluoroacetamide (3)
Ph
N
To a stirred soln of 4-aminobenzylamine (2, 1.10 g, 9 mmol) in de-
gassed MeOH (15 mL) at 0 °C was added dropwise methyl trifluo-
roacetate (0.90 mL, 9 mmol). After 15 min, the ice bath was
removed and the mixture was stirred at r.t. for a further 1 h. Then,
the mixture was concentrated under reduced pressure and the resi-
due was recrystallized (Et2O) to yield 3 (1.88 g, 96%) as colorless
crystals; mp 112 °C.
H
CHO
H+
PhNH2
NH
H
NH
H
– H2O
N
N
1H NMR (300 MHz, DMSO-d6): d = 4.19 (d, J = 5.6 Hz, 2 H), 5.02
(s, 2 H, NH2), 6.52 (d, J = 8.3 Hz, 2 H), 6.94 (d, J = 8.3 Hz, 2 H),
9.78 (br t, J = 5.6 Hz, 1 H, NH).
R
R
13C NMR (75.5 MHz, DMSO-d6): d = 42.3 (CH2), 113.7 (2 CH),
1
7 (yellow)
1
116.0 (q, JCF = 288 Hz), 124.2 (Cq), 128.5 (2 CH), 148.0 (Cq),
Ph
NH
Ph
156.0 (q, 2JCF = 36.5 Hz).
H
N
H
N
N
MS (EI): m/z (%) = 219 (10) [M + H]+, 218 (100) [M]+, 217 (13),
149 (4) [M – CF3]+, 121 (5) [M+ – CF3CO], 119 (6), 106 (86) [M –
CF3CONH]+, 77 (9), 65 (4).
H
Anal. Calcd for C9H9F3N2O (218.18): C, 49.55; H, 4.16; N, 12.84.
Found: C, 49.55; H, 4.22; N, 12.62.
N
H
NH
H
H
2,2,2-Trifluoro-N-(4-hydrazinobenzyl)acetamide Hydrochlo-
ride (4)
R
To a stirred suspension of 3 (2.72 g, 12.48 mmol) in 6 M HCl (40
mL) at –5 °C was slowly added aq NaNO2 soln (0.86 g, 12.48
mmol). The mixture was stirred at –5 °C for a further 30 min and
filtered and then added to a soln of SnCl2·2 H2O (14.40 g, 63.7
mmol) maintained at 0 °C. A white precipitate developed and the
suspension was stirred at 0 °C for a further 30 min and then left
overnight without stirring. The precipitate was collected by filtra-
tion and suspended in a mixture of concd HCl (0.7 mL) and H2O (41
mL), saturated with H2S. The white suspension turned dark brown.
The soln was stirred for 15 min and then filtered through Celite to
remove the SnS2. The filtrate was concentrated under reduced pres-
sure, the residue was treated with concd HCl and the precipitate was
collected by filtration to yield 4 (1.81 g, 54%) as a white, shiny pow-
der; mp 202 °C.
R
8 (orange-red)
Scheme 2 Proposal for the mechanism of the Schaeffer reaction
mation of the colors can be explained by the reaction
sequence given in Scheme 2. In the first step, aniline re-
acts with the aldehyde group of the schaefferal 1 to form
a yellow azomethine 7. Protonation of the imine nitrogen
then converts 7 into the delocalized cation 8, which could
explain the development of the orange-red color.
In conclusion, the structures of schaefferals A and B have
been confirmed by total synthesis, which afforded these
compounds in five steps from 4-aminobenzylamine with
overall yields of 12% and 7%, respectively. The aldehyde
group of the schaefferals offers an explanation for the for-
mation of the bright orange-red color in Schaeffer’s cross
reaction. The schaefferals 1 are new additions to a family
of hydrazine derivates occurring in Agaricus species.6,7
Further work is needed to evaluate their risk for human
consumption and to establish the final structure of schaef-
feral C (1c).
1H NMR (300 MHz, DMSO-d6): d = 4.30 (d, J = 6 Hz, 2 H, CH2),
6.97 (d, J = 8 Hz, 2 H), 7.19 (d, J = 8 Hz, 2 H), 8.31 (br, 1 H,
+
NHNH3 ), 10.00 (t, J = 6 Hz, 1 H, CH2NH), 10.31 (br s, 3 H,
+
NHNH3 ).
13C NMR (75.5 MHz, DMSO-d6): d = 42.1 (CH2), 114.5 (2 CH),
1
116.0 (q, JCF = 288 Hz), 128.2 (2 CH), 130.4 (Cq), 144.8 (Cq),
156.2 (q, 2JCF = 36 Hz).
MS (EI): m/z (%) = 234 (8) [M – HCl + H]+, 233 (100) [M – HCl]+,
232 (6), 218 (5), 202 (6), 121 (31), 104 (5).
Anal. Calcd for C9H10F3N3O·HCl (269.65): C, 40.09; H, 4.11; N,
15.58; Cl, 13.15. Found: C, 40.11; H, 4.33; N, 15.55; Cl, 13.18.
Hydrazones 5; General Procedure
Melting points (uncorrected): Reichert Thermovar hot stage micro-
scope. UV/Vis: Perkin-Elmer Lambda-16. IR: Perkin-Elmer Spec-
trum-1000. NMR: Bruker ARX 300, relative to DMSO-d6
(dH = 2.49, dC = 39.7) and acetone-d6 (dH = 2.04, dC = 29.8) as inter-
nal standard. MS (EI, 70 eV): Finnigan MAT 90 and Finnigan MAT
95Q. HRMS (EI, 70 eV): Finnigan MAT 95Q. TLC: Silica gel 60
Hydrazine 4 (200 mg, 0.74 mmol) was suspended in AcOH (0.5
mL) and H2O (10 mL), and the mixture was adjusted to pH 5 by ad-
dition of NaOAc. Then, a soln of the aromatic aldehyde (0.75
mmol) in MeOH (20 mL) was added. The mixture was stirred over-
night and the precipitate was collected by filtration and dissolved in
EtOAc. The soln was washed with H2O (3 ×), dried (MgSO4), and
concentrated under reduced pressure to yield the solid hydrazone 5.
A second batch of 5 was obtained by extraction of the filtrate with
EtOAc, the combined organic phases were washed with H2O and
dried (MgSO4) and the concentrated soln was subjected to chroma-
tography (silica gel).
F
254 aluminum foils (Merck). Column chromatography: silica gel 60
(40–63 mm, Merck). HPLC: Analytical HPLC: Waters M 6000A
pump with gradient controller and photodiode array detector M 990
equipped with a Knauer Lichrosorb RP-18 column (7 mm, 250 × 4
mm). Elemental analyses were performed by the Microanalytical
Laboratory, Ludwig-Maximilians-Universität München. 4-Amino-
benzylamine (2) was purchased from Sigma-Aldrich.
Synthesis 2010, No. 13, 2287–2291 © Thieme Stuttgart · New York

PAPER
Synthesis of Schaefferals
2289
N-[4-(N¢-Benzylidenehydrazino)benzyl]-2,2,2-trifluoroacet-
amide (5a)
UV/Vis (MeOH): lmax (log e) = 204 (4.51), 263 (4.21), 418 nm
(4.39).
Following the general procedure using benzaldehyde (0.08 mL,
0.81 mmol). Chromatography (CHCl3–MeOH, 100:1) afforded 5a
as a white solid; total yield: 162 mg (68%); mp 175 °C.
Anal. Calcd for C16H13F3N4O3 (366.29): C, 52.46; H, 3.58; N,
15.30. Found: C, 52.69; H, 3.79; N, 15.31.
1H NMR (300 MHz, DMSO-d6): d = 4.29 (d, J = 5.7 Hz, 2 H), 7.04
(d, J = 8.7 Hz, 2 H), 7.15 (d, J = 8.7 Hz, 2 H), 7.28 (‘t’, J = 7.2 Hz,
1 H), 7.38 (‘t’, J = 7.2 Hz, 2 H), 7.64 (‘d’, J = 7.2 Hz, 2 H), 7.85 (s,
1 H, CH=N), 9.88 (br t, J = 5.7 Hz, 1 H, NH), 10.35 (br s, 1 H, NH).
Amines 6; General Procedure for Hydrolysis of N-Trifluoro-
acetyl Derivatives 5
All steps were carried out under argon with degassed solvents. The
N-trifluoroacetyl derivative 5 (10 mmol) was dissolved in MeOH–
H2O. Then, excess Ba(OH)2·8 H2O was added and the mixture was
kept at r.t. After disappearance of the starting material (TLC con-
trol), the suspension was extracted with EtOAc and the extract was
washed with H2O (3 ×). The combined extracts were dried (MgSO4)
and concentrated under reduced pressure to yield the oily amine 6.
13C NMR (75.5 MHz, DMSO-d6): d = 43.7 (CH2), 113.2 (2 CH),
1
117.2 (q, JCF = 287 Hz), 126.7 (2 CH), 128.8 (CH), 128.9 (Cq),
129.4 (2 CH), 129.9 (2 CH), 137.0 (Cq), 137.9 (CH), 146.0 (Cq),
157.4 (q, 2JCF = 36.4 Hz).
MS (EI): m/z (%) = 322 (19) [M + H]+, 321 (100) [M]+, 217 (5), 209
(13) [M – NHCOCF3]+, 106 (7), 104 (6), 77 (7).
4-(N¢-Benzylidenehydrazino)benzylamine (6a)
From 5a (150 mg, 0.47 mmol) and Ba(OH)2·8 H2O (6.00 g, 19.03
mmol) in H2O (20 mL) and MeOH (50 mL); 6a (68 mg, 65%) was
obtained as a brown oil.
1H NMR (300 MHz, DMSO-d6): d = 2.63 (br s, 2 H, NH2), 3.62 (s,
2 H, CH2), 7.02 (d, J = 8.6 Hz, 2 H), 7.18 (d, J = 8.6 Hz, 2 H), 7.27
(‘t’, J = 7.4 Hz, 1 H), 7.38 (‘t’, J = 7.4 Hz, 2 H), 7.63 (‘d’, J = 7.4
Hz, 2 H), 7.84 (s, 1 H, CH=N), 10.26 (s, 1 H, NH).
UV/Vis (MeOH): lmax (log e) = 202 (4.50), 235 (4.15), 307 (4.13),
345 (4.41), 429 nm (1.38).
Anal. Calcd for C16H14F3N3O (321.30): C, 59.81; H, 4.39; N, 13.08.
Found: C, 59.72; H, 4.48; N, 13.31.
2,2,2-Trifluoro-N-{4-[N¢-(4-hydroxybenzylidene)hydrazi-
no]benzyl}acetamide (5b)
13C NMR (75.5 MHz, acetone-d6): d = 45.2 (CH2), 111.7 (2 CH),
125.4 (2 CH), 127.6 (Cq), 127.8 (2 CH), 128.5 (2 CH), 134.4 (Cq),
135.79 (CH), 135.83 (CH), 143.7 (Cq).
Following the general procedure using 4-hydroxybenzaldehyde (91
mg, 0.75 mmol). Chromatography (EtOAc–hexanes, 2:3) yielded
5b as a slightly pinkish solid; total yield: 149 mg (60%); mp 182 °C.
MS (EI): m/z (%) = 226 (14) [M + H]+, 225 (100) [M]+, 224 (20),
210 (6), 209 (38), 120 (10), 106 (13), 94 (14), 77 (7).
HRMS: m/z [M]+ calcd for C14H15N3: 225.1174; found: 225.1120.
IR (KBr): 3312 (s), 1705 (s), 1614 (s), 1555 (m), 1528 (m), 1514 (s),
1263 (s), 1217 (s), 1177 (s), 1135 (m), 1096 (m), 996 (w), 981 (w),
945 (w), 912 (w), 836 (m), 804 (w), 727 (w), 651 (w), 601 (w), 529
(w), 435 cm–1 (w).
1H NMR (300 MHz, DMSO-d6): d = 4.27 (d, J = 5.4 Hz, 2 H), 6.78,
6.98, 7.11, 7.46 (each d, J = 8.5 Hz, 2 H), 7.77 (s, 1 H), 9.61 (s, 1 H,
OH), 9.87 (br t, J = 5.4 Hz, 1 H, NH), 10.06 (br s, 1 H, NH).
4-{[4-(Aminomethyl)phenyl]hydrazonomethyl}phenol (6b)
From 5b (120 mg, 0.36 mmol) and Ba(OH)2·8 H2O (2.50 g, 7.93
mmol) in H2O (10 mL) and MeOH (10 mL); 6b (61 mg, 71%) was
obtained as a brownish oil.
1H NMR (300 MHz, DMSO-d6): d = 3.62 (s, 2 H, CH2), 4.36 (br s,
3 H, NH2, OH), 6.78 (d, J = 8.1 Hz, 2 H), 6.96 (d, J = 8.0 Hz, 2 H),
7.15 (d, J = 8.0 Hz, 2 H), 7.46 (d, J = 8.1 Hz, 2 H), 7.76 (s, 1 H,
CH=N), 9.97 (br s, 1 H, NH).
13C NMR (75.5 MHz, DMSO-d6): d = 42.3 (CH2), 111.6 (2 CH),
1
115.5 (2 CH), 116.0 (q, JCF = 288.5 Hz), 126.7 (Cq), 126.8 (Cq),
127.1 (2 CH), 128.6 (2 CH), 137.3 (CH), 145.0 (Cq), 156.1 (q,
2JCF = 36.1 Hz), 157.8 (Cq).
MS (EI): m/z (%) = 338 (19) [M + H]+, 337 (100) [M]+, 225 (10) [M
– NHCOCF3]+, 120 (6), 106 (7).
13C NMR (75.5 MHz, DMSO-d6): d = 45.0 (CH2), 111.4 (2 CH),
115.5 (2 CH), 126.8 (Cq), 127.0 (2 CH), 128.0 (2 CH), 133.0 (Cq),
136.7 (CH), 144.3 (Cq), 157.7 (Cq).
UV (MeOH): lmax (log e) = 202 (4.47), 249 (4.02), 306 (4.26), 346
nm (4.40).
MS (EI): m/z (%) = 242 (15) [M + H]+, 241 (100) [M]+, 240 (17),
225 (22) [M – NH2]+, 224 (18), 122 (8), 121 (13), 120 (25),119 (9),
106 (18), 94 (32), 93 (17), 77 (14), 65 (15).
Anal. Calcd for C16H14F3N3O2 (337.30): C, 56.97; H, 4.18; N,
12.46. Found: C, 56.95; H, 4.16, N, 12.30.
HRMS: m/z [M]+ calcd for C14H15N3O: 241.1171; found: 241.1193.
2,2,2-Trifluoro-N-{4-[N¢-(4-nitrobenzylidene)hydrazino]ben-
zyl}acetamide (5d)
Following the general procedure using 4-nitrobenzaldehyde (112
mg, 0.74 mmol). Immediately, a blood-red precipitate was formed.
The mixture was stirred at r.t. for 5 h. Chromatography (EtOAc–
hexanes, 1:2) yielded 5d (256 mg, 94%); mp 196 °C.
4-[N¢-(4-Nitrobenzylidene)hydrazino]benzylamine (6d)
From 5d (225 mg, 0.61 mmol) and Ba(OH)2·8 H2O (4.70 g, 14.9
mmol) in H2O (10 mL) and MeOH (25 mL); 6d (147 mg, 89%) was
obtained as a dark red oil.
1H NMR (300 MHz, DMSO-d6): d = 4.31 (d, J = 5.7 Hz, 2 H), 7.12
(d, J = 8.6 Hz, 2 H), 7.19 (d, J = 8.6 Hz, 2 H), 7.87 (d, J = 9 Hz, 2
H), 7.94 (s, 1 H), 8.22 (d, J = 9 Hz, 2 H), 9.91 (br t, J = 5.7 Hz, 1 H,
NH), 10.90 (br s, 1 H, NH).
1H NMR (300 MHz, DMSO-d6): d = 3.70 (s, 2 H, CH2), 3.78 (br s,
2 H, NH2), 7.11 (d, J = 8.1 Hz, 2 H), 7.25 (d, J = 8.1 Hz, 2 H), 7.85
(d, J = 9 Hz, 2 H), 7.92 (s, 1 H, CH=N), 8.21 (d, J = 9 Hz, 2 H),
10.92 (1 H, NH).
13C NMR (75.5 MHz, DMSO-d6): d = 44.4 (CH2), 112.3 (2 CH),
124.0 (2 CH), 125.8 (2 CH), 128.5 (2 CH), 133.2 (Cq), 142.6 (CH),
143.2 (Cq), 145.8 (Cq) (1 Cq obscured).
MS (EI): m/z (%) = 271 (16) [M + H]+, 270 (100) [M]+, 269 (32),
254 (26) [M – NH2]+, 240 (8), 208 (5), 178 (5), 121 (9) [C7H9N2],
120 (21), 106 (9), 94 (19), 77 (6).
13C NMR (75.5 MHz, DMSO-d6): d = 42.2 (CH2), 112.5 (2 CH),
1
116.0 (q, JCF = 288 Hz), 123.9 (2 CH), 125.9 (2 CH), 128.67 (2
CH), 128.71 (Cq), 133.6 (Cq), 142.5 (CH), 143.7 (Cq), 145.9 (Cq),
156.1 (q, 2JCF = 36 Hz).
MS (EI): m/z (%) = 367 (17) [M + H]+, 366 (100) [M]+, 349 (5), 319
(7), 254 (14) [M – NHCOCF3]+, 217 (5), 147 (6), 122 (5), 106 (6),
104 (7), 94 (5), 77 (5).
HRMS: m/z [M]+ calcd for C14H14N4O2: 270.1058; found:
270.1087.
Synthesis 2010, No. 13, 2287–2291 © Thieme Stuttgart · New York

2290
R. Kileci-Ksoll et al.
PAPER
Aldehydes 1; General Procedure from Amines 6
The spectroscopic data of synthetic 1b agreed with those of the nat-
ural product, and the identity of both compounds was confirmed by
HPLC comparison including co-chromatography.
To a soln of amine 6 (1 equiv) and isonicotinaldehyde (2.2 equiv) in
DMF was added DBU (1 equiv) and the mixture was stirred at r.t.
overnight. The color of the soln changed from initially dark green
to dark red. The reaction was quenched with aq 1.1 M KHSO4 (20
mL) and the resulting suspension stirred for an additional 30 min.
H2O and Et2O were added, and the aqueous phase was extracted
several times with Et2O. The combined organic phases were dried
(MgSO4) and concentrated, and the resulting residue was purified
by chromatography (silica gel).
4-[N¢-(4-Nitrobenzylidene)hydrazino]benzaldehyde (1d)
From amine 6d (96 mg, 0.36 mmol), isonicotinaldehyde (0.073 mL,
0.78 mmol), and DBU (0.054 mL, 0.36 mmol) in DMF (10 mL).
The soln was stirred overnight and then treated with 1.1 M aq
KHSO4 (10 mL). Usual work-up yielded an oil, which was purified
by column chromatography (EtOAc–hexanes, 2:1) to afford 1d (34
mg, 36%) as a dark red solid; mp 213 °C.
Schaefferal A (1a)
1H NMR (300 MHz, DMSO-d6): d = 7.27 (d, J = 8.5 Hz, 2 H, H3,
H5), 7.80 (d, J = 8.5 Hz, 2 H, H2, H6), 7.95 (d, J = 8.7 Hz, 2 H, H2¢,
H6¢), 8.07 (s, 1 H, H7¢), 8.24 (d, J = 8.7 Hz, 2 H, H3¢, H5¢), 9.77 (s,
1 H, H7), 11.42 (br s, 1 H, NH).
13C NMR (75.5 MHz, acetone-d6): d = 112.2 (2 CH), 123.9 (2 CH),
126.7 (2 CH), 128.4 (Cq), 131.7 (CH), 137.4 (Cq), 141.5 (2 CH),
146.6 (Cq), 149.4 (Cq), 190.5 (CHO).
From amine 6a (260 mg, 1.16 mmol), isonicotinaldehyde (0.23 mL,
2.41 mmol), and DBU (0.16 mL, 1.07 mmol) in DMF (10 mL). The
reaction was quenched with aq 1.1 M KHSO4 (5 mL). After workup,
the resulting brown oil was chromatographed (EtOAc–hexanes,
1:2) to yield 1a (141 mg, 55%) as a yellow-ochre solid; mp 127 °C;
Rf = 0.39 (CH2Cl2).
IR (KBr): 3436 (m, br), 3253 (m), 1664 (m), 1604 (s), 1591 (s),
1578 (s), 1539 (s), 1303 (s), 1270 (s), 1219 (m), 1151 (m), 1128 (m),
1096 (m), 1070 (m), 694 cm–1 (m).
1H NMR (300 MHz, acetone-d6): d = 7.29 (d, J = 8.7 Hz, 2 H, H3,
H5), 7.36 (‘t’, J = 7.0 Hz, 1 H, H4¢), 7.42 (‘t’, J = 7.0 Hz, 2 H, H3¢,
H5¢), 7.74 (‘d’, J = 7.0 Hz, 2 H, H2¢, H6¢), 7.80 (d, J = 8.7 Hz, 2 H,
H2, H6), 8.01 (s, 1 H, H7¢), 9.81 (s, 1 H, H7), 10.07 (br s, 1 H, NH).
MS (EI): m/z (%) = 270 (17) [M + H]+, 269 (100) [M]+, 268 (15) [M
– H]+, 239 (10), 120 (9), 119 (5), 92 (13), 65 (7).
HRMS: m/z [M]+ calcd for C14H11N3O3: 269.0763; found:
269.0782.
UV/Vis (MeOH): lmax (log e) = 247 (4.05), 324 (4.09), 408 nm
(4.54).
13C NMR (75.5 MHz, acetone-d6): d = 112.8 (C3, C5), 123.3 (C1¢),
127.2 (C2¢, C6¢), 129.5 (C3¢, C5¢), 129.7 (C2, C6), 132.5 (C4¢),
136.3 (C1), 141.2 (C7¢), 151.2 (C4), 190.5 (CHO).
Acknowledgment
MS (EI, DI, 150 °C): m/z (%) = 225 (16) [M + 1]+, 224 (100) [M]+,
This work was financially supported by the Bundesministerium für
Bildung und Forschung and the Fonds der Chemischen Industrie.
We thank Dr. Kay Greenfield, Brisbane, for her help in improving
the manuscript.
223 (16), 195 (5) [M – CHO]+, 120 (10) [C7H6NO], 92 (7), 77 (5).
HRMS: m/z [M]+ calcd for C14H12N2O: 224.0863; found: 224.0906.
UV/Vis (MeOH): lmax (log e) = 240 (4.13), 310 (3.69), 372 nm
(4.68).
References
The spectroscopic data of synthetic 1a agreed with those of the nat-
ural product, and the identity of both compounds was confirmed by
HPLC comparison including co-chromatography.
(1) (a) Schäffer, J. Schweiz. Z. Pilzk. 1933, 11, 137.
(b) Schäffer, J. Dtsch. Blätter Pilzk. 1943, 5, 1.
(c) Schäffer, J.; Möller, P. Ann. Myc. 1938, 36, 64.
(2) (a) Hilbig, S. Ph.D. Thesis; University of Bonn: Germany,
1986. (b) Kileci-Ksoll, R. Ph.D. Thesis; University of Bonn:
Germany, 1989, details of the isolation procedure and the
structural elucidation of schaefferals A and B will be given
in a separate publication.
Schaefferal B (1b)
From amine 6b (200 mg, 0.83 mmol), isonicotinaldehyde (0.17 mL,
1.80 mmol), and DBU (0.13 mL, 0.83 mmol) in DMF (5 mL). The
reaction was quenched with aq 1.1 M KHSO4 (10 mL). After work-
up, the resulting oil was chromatographed (EtOAc–hexanes, 2:1) to
yield nearly pure 1b (66 mg, 33%) as a yellow solid. An analytically
pure sample was obtained by preparative HPLC (RP-18 column) as
a lemon yellow solid; mp 211 °C; Rf = 0.52 (EtOAc–hexanes, 1:1).
(3) Ohta, S.; Okamoto, M. Synthesis 1982, 756.
(4) The obvious synthesis of 1 from 4-(hydroxymethyl)phenyl-
hydrazine and aromatic aldehydes and subsequent oxidation
of the resulting (hydroxymethyl)-phenylhydrazones is less
effective and afforded schaefferals A and B only in 15% and
3.5% yield, respectively (Kilecy-Ksoll, R.; Steglich, W.
unpublished). The approach is hampered by difficulties in
the conversion of the hydroxymethyl group into the
aldehyde group in presence of the hydrazone moiety. Most
of the common reagents for this transformation, e.g. MnO2,
Ni2O3, and PDC or PCC, were either ineffective or led to
partial cleavage of the hydrazone function. The problem
could finally be solved by the use of nicotinium dichromate,
cf.: López, C.; González, A.; Cossio, F. P.; Palomo, C. Synth.
Commun. 1985, 15, 1197.
(5) Frank found that nitric acid is not mandatory for the
Schaeffer reaction and that it can also be performed with
other acids such as HCl and H2SO4, or even AcOH; see:
Frank, H. M. Z. Mykol. 1988, 54, 103; his suggestion that the
red color may be due to azo dye formation via coupling of a
diazonium ion is invalidated by our results.
IR (KBr): 3430 (s, br), 3306 (m), 1663 (m), 1595 (s), 1536 (m),
1513 (s), 1271 (m), 1225 (m), 1161 (m), 1127 (m), 834 cm–1 (m).
1H NMR (300 MHz, acetone-d6): d = 6.89 (d, J = 9.0 Hz, 2 H, H3,
H5), 7.24 (d, J = 8.7 Hz, 2 H, H3¢, H5¢), 7.60 (d, J = 8.7 Hz, 2 H,
H2¢, H6¢), 7.77 (d, J = 9.0 Hz, 2 H, H2, H6), 7.94 (s, 1 H, H7¢), 8.67
(br s, 1 H, OH), 9.78 (s, 1 H, H7), 9.87 (br s, 1 H, NH).
13C NMR (75.5 MHz, CD3OD): d = 112.6 (C3, C5), 116.6 (C3¢,
C5¢), 128.8 (C1¢), 129.1 (C2, C6 and C2¢, C6¢), 133.4 (C1), 142.5
(C7¢), 152.7 (C4), 159.9 (C4¢), 192.5 (CHO).
MS (EI, DI 180 °C): m/z (%) = 241 (15) [M + H]+, 240 (100) [M]+,
239 (7), 121 (6), 120 (25), 119 (14), 93 (8), 92 (10), 91 (9).
HRMS: m/z [M]+ calcd for C14H12N2O2: 240.0861; found:
240.0880.
UV/Vis (MeOH): lmax (log e) = 233 (3.90), 275 (3.37), 303 (3.72),
308 (3.73), 311 (3.75), 377 nm (4.52).
Synthesis 2010, No. 13, 2287–2291 © Thieme Stuttgart · New York

PAPER
(6) See, for example, agaritine: (a) Levenberg, B. J. Am. Chem.
Synthesis of Schaefferals
2291
(7) The biosynthesis of the schaefferals 1 from 4-(hydroxy-
methyl)phenylhydrazine and aromatic aldehydes appears
plausible. It is supported by the fact that these likely
precursors occur in certain Agaricus species.
Soc. 1961, 83, 503. (b) Baumgartner, D.; Hoesch, L.; Rast,
D. M. Phytochemistry 1998, 49, 465; and references cited
therein. Agaritinal: (c) Chulia, A. J.; Bernillon, J.; Favre-
Bonvin, J.; Kaouadji, M.; Arpin, N. Phytochemistry 1988,
27, 929. 4-(Hydroxymethyl)phenylhydrazine: (d) Toth, B.;
Nagel, D.; Patil, K.; Erickson, J.; Antonson, K. Cancer Res.
1978, 38, 177. Xanthodermin: (e) Hilbig, S.; Andries, T.;
Steglich, W.; Anke, T. Angew. Chem., Int. Ed. Engl. 1985,
24, 1063; Angew. Chem. 1985, 97, 1063.
Synthesis 2010, No. 13, 2287–2291 © Thieme Stuttgart · New York