Longiberine and O-methyllongiberine, dimeric protoberberine-benzyl tetrahydroisoquinoline alkaloids from Thalictrum longistylum

Article abstract of DOI:10.1021/np9902284

Two benzyltetrahydroisoquinoline - protoberberine dimers, longiberine (1) and O-methyllongiberine (2): were isolated from the roots of Thalictrum longistylum and represent a new class of dimeric alkaloids. The structure of longiberine (1) was established by spectral and chemical methods. Reductive cleavage of O-ethyllongiberine (4) with Na/liquid NH₃ yielded (+)-(S)-N- methylcoclaurine (5), which determined one-half of the dimer, and 1D and 2D NMR studies arranged the substituents on the protoberberine nucleus. Chemical conversion of thalidezine (6) to 1 via the O-acetyl N,N-didemethyl derivative 9, which was methylenated in the Mannich reaction and N-methylated by the Eschweiler-Clarke procedure, established the second asymmetric center as S and confirmed the ring size and the order of the substituents for 1. Methylation of 1 with diazomethane formed the O-methyl derivative 2, identical with the natural product.

Full text of DOI:10.1021/np9902284

1410
J . Nat. Prod. 1999, 62, 1410-1414
Lon giber in e a n d O-Meth yllon giber in e, Dim er ic P r otober ber in e-Ben zyl
Tetr a h yd r oisoqu in olin e Alk a loid s fr om Th a lictr u m lon gistylu m 1
Shoei-Sheng Lee,† Wu-Nan Wu,‡ J ohn H. Wilton,§ J ack L. Beal, and Raymond W. Doskotch*
Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University,
Columbus, Ohio 43210-1291
Received May 12, 1999
Two benzyltetrahydroisoquinoline-protoberberine dimers, longiberine (1) and O-methyllongiberine (2),
were isolated from the roots of Thalictrum longistylum and represent a new class of dimeric alkaloids.
The structure of longiberine (1) was established by spectral and chemical methods. Reductive cleavage
of O-ethyllongiberine (4) with Na/liquid NH3 yielded (+)-(S)-N-methylcoclaurine (5), which determined
one-half of the dimer, and 1D and 2D NMR studies arranged the substituents on the protoberberine
nucleus. Chemical conversion of thalidezine (6) to 1 via the O-acetyl N,N-didemethyl derivative 9, which
was methylenated in the Mannich reaction and N-methylated by the Eschweiler-Clarke procedure,
established the second asymmetric center as S and confirmed the ring size and the order of the substituents
for 1. Methylation of 1 with diazomethane formed the O-methyl derivative 2, identical with the natural
product.
The large family of benzylisoquinoline alkaloids contains
a homodimeric class of several hundred members, the so-
called bisbenzylisoquinolines, in addition to the smaller
numbered heterodimers. In these the monomeric units are
alkaloids derived biosynthetically from benzyltetrahydroiso-
quinolines.2-4 The derived alkaloids, themselves, may form
homodimers. The majority are biphenyl and/or diphenyl
ether connected and could contain up to three linkages. Of
the heterodimers, the aporphine-benzylisoquinolines2a,5
are the largest group, while the aporphine-pavine,1,2b
pavine-benzylisoquinoline,2c and cularine-morphinan2d
groups are represented by only a few examples. For
protoberberines, no heterodimers, and only two homodimers,
are recorded.2e
This report is on the first protoberberine-benzyltetra-
hydroisoquinoline dimers, longiberine (1) and its O-methyl
derivative 2, obtained from the roots of Thalictrum
longistylum DC. (Ranunculaceae). Earlier publications
described 12 alkaloids from this plant, some of which
possess hypotensive and antimicrobial activities.6,7
at δ 2.33 in the 1H NMR spectrum. The remaining two
oxygens must be diphenyl ethers. The absence of a NH
group as supported by lack of formation of an acetamide
on acetylation and the total carbon-bound protons from the
multiplicities of the 13C NMR off-resonance decoupled and
DEPT experiments, together with the phenolic proton,
accounted for all the required hydrogens. The presence of
seven methylene carbons (DEPT) was revealing, and
comparing the methine and methylene chemical shifts to
those of typical bisbenzyl tetrahydroisoquinolines showed
one methine upfield and one methylene downfield from the
usual positions. In 1, they overlapped at δ 57.2 and could
be assigned to positions C-8 and C-14 of a protoberberine
unit.8 This type of unit was supported by the presence of
an isolated AB quartet for H2-8 at δ 4.06 and 3.97 (J )
15.2 Hz).9
To gain information about the nature of the monomeric
units, the classic Na/liquid NH3 reductive cleavage proce-
dure was applied to O-ethyllongiberine (4), which gave
(+)-(S)-N-methylcoclaurine (5) as a phenolic product and
was identified from its physical properties (TLC, IR, 1H
NMR, specific rotation, and CD) when compared to an
authentic sample.10 This established the “left-hand” unit,
leaving three methoxyls and the phenolic group for the
protoberberine component.
Resu lts a n d Discu ssion
Longiberine (1) was obtained from the phenolic and
nonphenolic Et2O-soluble tertiary alkaloid fractions as a
crystalline material, mp 169-170 °C, and showed a HRMS
molecular ion as base peak, corresponding to the formula
The HRMS of 1, with a fragment ion at m/z 462 (C27H28
-
C
38H40N2O7. The formula and the intense molecular ion
NO6) was formed by loss of the tetrahydroisoquinoline from
cleavage between C-7′ and its oxygen and between C-1′ and
the C-9′ benzylic carbon, along with accepting a proton.11
Also, fragment ions at m/z 397 (C22H25N2O5) and 239
(C16H15O2) from a retro-Diels-Alder fragmentation12 of ring
C of the protoberberine and cleavage between the benzylic
carbon and the tetrahydroisoquinoline ring supported the
head-to-head dimerization and location of the phenolic
group in ring A. The fragment ion m/z 411 (C23H27N2O5)
from the O-methyl derivative 2 being 14 daltons larger
than the m/z 397 fragment from 1 confirmed the ring A
location of the phenolic hydroxyl (see below).
peak support a dimeric structure with at least two linkages,
most probably diphenyl ethers. The 1H NMR spectrum
showed one N-methyl and four O-methyl groups, leaving
three unassigned oxygens, one of which must be a phenolic
hydroxyl from the presence of absorption at 3540 cm-1 in
the IR spectrum and the bathochromic shift with strong
alkali in the UV spectrum. This was confirmed by forma-
tion of the monoacetate 3 showing a three-proton singlet
* To whom correspondence should be addressed. Tel.: (614) 292-6596.
Fax: (614) 292-2435. E-mail: doskotch@dendrite.pharmacy.ohio-state.edu.
† Current Address: School of Pharmacy, National Taiwan University,
Taipei, Taiwan, Republic of China.
1
The H-1H COSY and homonuclear decoupling experi-
‡ Current Address: R. W. J ohnson Pharmaceutical Research Institute,
Spring House, PA.
ments identified two 3-spin systems formed from a methine
and a methylene (H-14, H2-13 and H-1′, H2-9′), and a 4-spin
aromatic system for a 1,4-disubstituted benzene. Placement
§ Current Address: Millard Filmore Hospital, Clinical Pharmacokinetics
Laboratory, Buffalo, NY.
Deceased February 24, 1998.
10.1021/np9902284 CCC: $18.00
© 1999 American Chemical Society and American Society of Pharmacognosy
Published on Web 09/14/1999

Alkaloids from Thalictrum
J ournal of Natural Products, 1999, Vol. 62, No. 10 1411
F igu r e 1. NOED enhancements (in percent) for longiberine (1) at 300
MHz in CDCl3.
alkaloid isolated from the nonphenolic Et2O-soluble tertiary
alkaloid fraction. Its NMR spectral features are found in
Table 1.
The biosynthesis of 1 undoubtedly occurs from 6 and,
similarly, 2 most likely comes from hernandezine (10).10
Indirect evidence comes from the Macheta collection of
T. longistylum, from which 1 was not obtained but instead
gave an excellent yield of 6 (2.6 g from 5.4 kg of roots).
More importantly, if the biosynthesis involved phenol
coupling of a preformed protoberberine, it would have to
be 2,3,10-trioxygenated or 2,3,4,10-tetraoxygenated. The
authors are unaware of any naturally occurring proto-
berberines with only one oxygen in ring D. The six
protoberberines isolated from T. longistylum are all 9,10-
dioxygenated.7
of the substituents in the protoberberine unit and chemical
shift assignments of the protons in 1 were made by NOESY
and NOED experiments (Figure 1). The 2D NMR CH-
correlation and COLOC experiments allowed the 13C NMR
assignments to be made except for the methylene carbons
C-5, C-6, C-3′, C-4′, which were based on comparison with
those of model monomeric units,13,14 and the quaternary
carbons C-1 and C-4, which were distinguished by their
appearance in the fully 1H-coupled 13C NMR spectrum. C-1
(δ 141.0) appears as a very sharp singlet, while C-4 (δ
140.0) is more broadened and must result from the former
having only one proton (H-14) three-bonds away, while the
latter has two (H2-5), as well as the phenolic proton.
Comparing the structures of 1 and thalidezine (6),10 also
isolated from T. longistylum,15 indicated a very close
relationship; and examining a Dreiding model of 6 showed
that one of its conformations very easily led to a ring
closure in which the N-methyl of the highly oxygenated
tetrahydroisoquinoline ring could generate the C-8 meth-
ylene of the protoberberine unit (Figure 1). This cyclization
is not unlike the biosynthetic process well documented for
converting benzyl tetrahydroisoquinolines to protober-
berines.16 On the other hand, no conformation was possible
that would allow cyclization with the N-methyl of the
coclaurine unit. A synthetic transformation of 6, with its
stereochemical structure well established, to 1 was devised
to confirm longiberine’s structure and determine the
absolute configuration at the protoberberine asymmetric
center (C-14).
The molecular shape (Figure 1) of 1 as seen from a
Dreiding model is triangular, with two of the sides, formed
from the protoberberine unit and the tetrahyroisoquinoline
ring, positioned at an angle of about 65°. They are nearly
planar, but with a twist about the diphenyl ether linkage
of about 40°. Both right- and left-handed twists appear
possible. Figure 1 shows the left-handed form. The benzylic
unit, at the base of the triangle, is positioned more or less
perpendicular to the general plane of the other two sides.
The spectral data best fits the conformation for the
protoberberine unit as one of the two possible cis-fused B/C
ring arrangements in which both rings are in the half-chair
conformation. It is supported by the weak Bohlmann band
Thalidezine (6) was first acetylated to 7, then N-
demethylated with 2,2,2-trichloroethyl chloroformate17 to
generate first 8 then 9 with Zn-HOAc. Product 9 was
treated with HCHO in HCl to form the protoberberine unit
via the Mannich reaction18 followed by the Eschweiler-
Clarke reductive N-methylation of the isoquinoline unit by
HCHO and HCO2H.19 During the last step, the acetate
group was conveniently lost and the final product was 1,
identical (TLC, IR, 1H NMR, and CD) with the natural
product. Thus, longiberine has the same S,S-stereochem-
istry, substitution pattern, and ring size as 6.
near 2800 cm-1 in the IR spectrum, which is observed for
20,21
such cases,
(although that absorption has been long
associated, when strong, with a trans disposition22) and by
a bulky substituent at C-1, which causes the equilibrium
to favor the cis form.14 Also, the 13C NMR chemical shift
values for C-5 (δ 23.8) and C-6 (δ 48.0) are within the
Longiberine (1) was treated with diazomethane, and the
O-methylated product 2 was found to be identical with an

1412 J ournal of Natural Products, 1999, Vol. 62, No. 10
Lee et al.
Ta ble 1. 1H and 13C NMR Data for 1 and 2a
1
2
position
δH
δC
multiplicity
COLOC
δH
δC
1
1a
2
3
4
141.0
123.1
141.4
137.8
140.0
116.6
23.8
s
s
s
s
s
s
t
143.2
122.9b
144.6
142.4
145.2
123.3b
24.3
MeO-2
MeO-3
4a
5
2.85 hm
2.79 hm
2.99 hm
2.77 hm
4.06 d (15.2)
3.97 d (15.2)
6
8
48.0
57.1
t
t
48.3
57.3
4.05 d (15.3)
3.99 d (15.3)
8a
9
129.5
111.2
149.4
149.2
121.9
133.7
34.8
s
d
s
s
d
s
t
H2-8, H-12, H-13R
129.5
111.3
149.5
149.4
122.1
133.6
35.3
6.68 s
6.26 s
6.68 s
10
11
12
12a
13
H-9, H-12, MeO-10
H-9
H-13R
H-8, H-9, H-13R
6.23 s
3.95R br d (13.9)
2.58â dd (13.1, 9.9)
3.51 br d (10.9)
3.27 s
3.06R d (13.4)
2.57â dd (12.7, 10.3)
3.50 d (10.0)
3.25 s
14
57.1
60.9
61.1
d
q
q
57.3
60.9
61.18
61.22
57.0
MeO-2
MeO-3
MeO-4
MeO-10
HO-4
1′
3.82 s
3.82 s
3.81 s
3.92 s
3.92 s
5.50 br s
3.67 dd (11.4, 3.6)
56.8
q
65.0
128.5
45.3
d
s
t
3.66 dd (1.5, 3.4)
3.40 hm
65.3
128.6
45.6
1a′
3′
H-5′, H-9â′
H-8′
3.37 hm
2.87 hm
2.96 hm
2.73 hm
4′
24.9
t
25.2
4a′
5′
6′
7′
8′
127.7
112.3
148.8
142.3
119.5
38.6
s
d
s
s
d
t
128.2
112.3
149.1
142.3
119.5
39.0
6.52 s
6.53 s
H-5′, H-8′, MeO-6′
H-5′, H-8′
5.96 s
3.20â dd (12.4, 3.8)
2.75R dd (12.2, 12.2)
5.97 s
3.20â dd (13.4, 3.6)
2.75R dd (13.4, 13.4)
9′
10′
11′
12′
13′
14′
15′
MeO-6′
MeN-2′
134.1
133.0
122.1
159.6
121.5
129.2
55.6
s
H-9â′, H-14′
H-12, H-15′
134.3
133.1
122.3
159.7
121.7
129.3
55.6
6.23 dd (8.8, 1.5)
6.33 dd (8.8, 1.5)
d
d
s
d
d
q
q
6.23 br d (8.8)
6.34 br d (8.8)
7.28 br s
7.28 br s
3.46 s
7.28 br s
7.28 br s
3.48 s
2.56 s
42.7
2.56 s
42.9
a
Taken at 300 MHz in CDCl3 with data point resolution of 0.4 Hz for 1H and 1.9 Hz for 13C and chemical shift (δ) in ppm as referenced
to TMS with residual solvent peak (CHCl3) taken as internal standard at 7.26 ppm for 1H and 77.2 ppm for 13C. Spin-coupled patterns
are designated as follows: s ) singlet, d ) doublet, t ) triplet, q ) quartet, br ) broad, and h ) hidden or overlapped. The spin coupling
b
constant (J ) is given in parenthesis in Hz. May be interchanged.
Exp er im en ta l Section
narrow ranges observed for a series of â-positioned C-13
substituted protoberberines.23 However, in 1, C-8 (δ 57.1)
is downfield 9 ppm units and best fits a trans ring fusion.
This is due, undoubtedly, to the absence in 1 of the C-13
pseudoaxial substituent with its upfield γ-shift effect. The
C-8 chemical shift does fit the predicted value (δ 57.0) for
10,11-dioxygenated protoberberine.14 Other data do not
agree with the empirical rules in the literature. For
Gen er a l Exp er im en ta l P r oced u r es. The instruments
used and general procedures followed have been reported.7,25
P la n t Ma ter ia l. T. longistylum was identified and collected
by Mr. Mauricio Pinzon in the region of Macheta, province of
Cundinamarca, Colombia, during J une and J uly 1982, and in
the region of Zipacon, Colombia, during February and March
1982. Herbarium specimens are on file in the College of
Pharmacy, Ohio State University. The air-dried roots when
received were dried at 40 °C for 2 days in a force-draft plant-
drying oven, then ground in a Wiley Mill.
example, the H-14 chemical shift of δ 3.51 is less than δ
24
3.8 and would require a trans orientation,
and this
anomaly cannot be explained by a shielding from the
isoquinoline ring at C-1, as it is positioned away and on
the opposite side of ring A. Furthermore, the H-14 pattern
(br d, J ) 10.9 Hz) does not agree with either the trans or
cis forms.14,23 Clearly, additional studies are warranted
before the conformation of the protoberberine ring is
settled.
Extr a ction a n d In itia l Isola tion P r oced u r e. Extraction
of the roots and fractionation of the crude extracts to give the
alkaloid fractions were performed as recorded for the initial
study of T. longistylum.7 The Macheta collection (5.4 kg) gave
1.47 g of the nonphenolic Et2O-soluble, 4.05 g of the phenolic
Et2O-soluble, and 14.0 g of the CHCl3-soluble alkaloids; while
the Zipacon collection (4.7 kg) gave 2.16, 1.34, and 14.7 g of
those alkaloids, respectively.

Alkaloids from Thalictrum
J ournal of Natural Products, 1999, Vol. 62, No. 10 1413
Isola tion of Lon giber in e (1) a n d O-Meth yllon giber in e
(2). The nonphenolic Et2O-soluble alkaloids (1.9 g) from the
Zipacon collection were chromatographed on Si gel (80 g) with
MeOH in CDCl3 mixtures of 1, 1.5, 2.5, 3, 4, 5, 7, 10, and 50%.
The effluent fractions were monitored by TLC on Si gel with
PhMe-Me2CO-NH4OH (25:25:1). The 2.5% MeOH in CHCl3
solvent gave a fraction (400 mg) containing 2, with Rf 0.42 on
TLC, which was further separated on 15.6 g of Si gel with
PhMe-Me2CO-NH4OH (15:5:1) from which 159 mg of residue
was purified on 5 g of Si gel with 1% MeOH in CHCl3 to give
100 mg of homogeneous amorphous 2. A fraction (131 mg)
eluted from the first column with 4% MeOH in CHCl3 was
crystallized from MeOH-Et2O to give 50 mg of 1 as white
rosettes, with Rf 0.25 on TLC.
MeOH in CHCl3 gave from the last solvent 10 mg of a yellow
solid: [R]24D +86° (c 0.76, MeOH); CD (c 6.0 × 10-3 M, MeOH)
(deg) [θ]290 +10 800, [θ]278 0, [θ]276 -2910, [θ]262 0, and [θ]230
+44 000; with TLC, IR, and 1H NMR identical with an
authentic sample of (+)-(S)-N-methylcoclaurine (5).10
Isola tion of Th a lid ezin e (6). The phenolic Et2O-soluble
alkaloid fraction (4.05 g) from the Macheta collection gave from
Me2CO-hexane 1.8 g of crystalline 6, mp 158 °C. The mother
liquor residue was chromatographed on Si gel (50 g) with
CHCl3 and MeOH-CHCl3 mixtures of 0.5, 1, 2, 5, 10, and 20%
to give 0.76 g of 6, Rf 0.41 on TLC with PhMe-Me2CO-NH4-
OH (25:25:1).
Th a lid ezin e a cet a t e (7): Thalidezine (6) (200 mg) was
treated with Ac2O (5 mL) and pyridine (2 mL) for 16 h at
ambient temperature, evaporated with aid of PhMe, and
chromatographed on Si gel (6 g) with CHCl3 (100 mL) and 2%
MeOH in CHCl3 (50 mL) to give 190 mg of acetate 7: HRMS
Lon giber in e (1) fr om th e P h en olic Et2O-Solu ble Al-
k a loid F r a ction . The alkaloid fraction (1.3 g) from the
Zipacon collection was chromatographed on 100 g of Si gel with
650 mL of CHCl3-MeOH-NH4OH (96:4:0.2). After 265 mL
of effluent, the next 125 mL contained 740 mg of residue that,
on recrystallization from MeOH-Et2O, gave 393 mg of 1.
m/z 680.3105 (74%, C40H44N2O8, -0.7 mmu), 453.2012 (100,
1
C
25H29N206, 1.4); H NMR (90 MHz, CDCl3) δ 7.36 (1H, dd, J
) 8.3, 1.9 Hz, H-11′), 7.14 (1H, dd, J ) 8.3, 2.2 Hz, H-12′),
6.85 (2H, br s, H-14 and H-15), 6.79 (1H, dd, J ) 8.3, 2.2 Hz,
H-14), 6.55 (1H, br s, H-11), 6.52 (1H, s, H-5′), 6.30 (1H, dd, J
) 8.3, 1.9 Hz, H-15′), 6.01 (1H, s, H-8′), 3.93 (3H, s, MeO-13),
3.70 (3H, s, MeO-6), 3.36 (3H, s, MeO-6′), 3.24 (3H, s, MeO-7),
2.64 (3H, s, MeN-2′), 2.31 (3H, s, Ac-5), 2.29 (3H, s, MeN-2).26
Lon giber in e (1): mp 169-170 °C; [R]25 +43.8° (c 0.56,
D
MeOH); CD (c 5 × 104 M, MeOH) (deg.) [θ]305 0, [θ]289 +37
300, [θ]278 0, [θ]271 -23 400 (sh), [θ]248 -142 000, [θ]238 0, [θ]218
+221 000 and [θ]202 0; UV (MeOH) λmax (log ꢀ) 283 (4.14), 240
(sh 4.42) and 221 (end absorption 4.77), (0.01 N KOH, MeOH)
288 (4.19), 244 (sh 4.41) and 220 (end absorption 4.88) nm; IR
(CHCl3) νmax 3540 (OH), 3100, 2940, 2803, 1610, 1510, 1470,
1203, 1100, 1040, 950, 876, and 857 cm-1; HRMS m/z 636.2815
Din or t h a lid ezin e (N,N′-d id em et h ylt h a lid ezin e) a c-
eta te (9): Thalidezine acetate (7) (106 mg), PhH (10 mL), and
trichloroethyl chloroformate (99 mg, 2.2 equiv.)17 were refluxed
for 1.5 h, another 45 mg of reagent was added and refluxed
overnight. The residue, after evaporation under vacuum, was
chromatographed on Si gel (5 g) with CHCl3 (30 mL) and 0.5%
MeOH in CHCl3 to give 92 mg of the dicarbamate 8 of which
36 mg in 90% HOAc (1 mL) was stirred with activated Zn
powder (36 mg) for 2 h. The mixture was filtered and the
residue washed with H2O. The combined filtrate and wash
were basified with NH4OH to pH 9 and extracted with CHCl3
(3 × 30 mL). The CHCl3 residue was purified by preparative
TLC on Si gel (20 × 20 cm2, 0.75 mm) with CHCl3-MeOH-
(100%, M+, C38H40N2O7, 3.2 ppm error), 462.1873 (7, C27H28
-
NO6, 9.5), 397.1744 (7, C22H25N2O5, 4.8), 239,1048 (1, C16H15O2,
9.9), 205.073 (18, C11H11NO3, 2.2), 192.1015 (51, C11H14NO2,
5.1), 175.0628 (95, C10H9NO2, 3.2) 149.0589 (2, C9H9O2, 9.1),
1
107.0512 (22, C7H7O, 14.1); H and 13C NMR see Table 1.
O-Meth yllon giber in e (2): amorphous; [R]24D +31 ° (c 0.21,
MeOH); CD (c 4.3 × 10-3 M, MeOH) (deg) [θ]304 0, [θ]285 +17
200, [θ]274 0, [θ]266 -8400 (sh), [θ]246 -66 500, [θ]237 0, and [θ]221
+77 400; UV (MeOH) λmax (log ꢀ) 282 (4.01), 242 (sh, 4.42) and
220 (end 4.82) nm and no change in 0.01 N KOH; IR (CHCl3)
νmax 3010, 2940, 2803, 1610, 1510, 1470, 1422, 1202, 1100,
1067, 873 and 857 cm-1; HRMS m/z 650.299 (100, C39H42N2O7,
dev 0.7 mmu), 476.2052 (10, C28H30NO6, -2.1), 411.2136 (9,
NH4OH (93:7:1) to give, from the major band, 15 mg of 9: [R]25
D
+200° (c 0.7, CHCl3); IR (CHCl3) νmax 3600-3200, 3000, 2930,
2830, 1760, 1605, 1582, 1505, 1455, 1420, 1255, 1225-1190,
1123, 1010, 960, 873, and 830 cm-1; HRMS m/z 652.2816 (M+,
C
23H27N2O5, 21.6), 192.0978 (11, C11H14NO2 -4.7), 174.0885
1
(39, C11H12NO, -3.4) and 106.0443 (17, C7H6O, 2.4); H and
C
38H40N2O8, -3.1 mmu); FABMS (glycerol) m/z 653 (27, MH+),
13C NMR, see Table 1.
611 (45, M+ -CH2CO), 93 (100); 1H NMR (500 MHz, CDCl3) δ
7.43 (1H, dd, J ) 8.2, 2.0 Hz, H-11′), 7.17 (1H, dd, J ) 8.2, 2.5
Hz, H-12′), 6.88 (1H, d, J ) 8.1 Hz, H-14), 6.85 (1H, dd, J )
8.2, 2.5 Hz, H-14′), 6.75 (1H, dd, J ) 8.1, 1.8 Hz, H-15), 6.52
(1H, s, H-5′), 6.423 (1H, d, J ) 1.8 Hz, H-11), 6.419 (1H, dd, J
) 8.0, 2.0 Hz, H-15′), 6.02 (1H, s, H-8′), 4.27 (1H, dd, J ) 11.1,
5.4 Hz, H-1′), 4.03 (1H, d, J ) 9.7 Hz, H-1), 3.96 (3H, s, MeO-
13), 3.73 (3H, s, MeO-6), 3.40 (3H, s, MeO-6′), 3.34 (3H, s, MeO-
7), 3.30 (1H, dd, J ) 11.4, 5.0 Hz, H-9â′), 3.04 (1H, dd, J )
11.4, 11.4 Hz, H-9R′) 2.79 (1H, dd, J ) 13.6, 10.4 Hz, H-9â),
2.60 (1H, d, J ) 13.2 Hz, H-9R), 2.32 (3H, s, Ac-5).26
Lon gib er in e a cet a t e (3): Longiberine (1) (8 mg) was
treated with Ac2O in pyridine and the product purified as
described,1 with final purification on a Si gel (3 g) column with
1.0 and 1.5% MeOH in CHCl3 to give 7 mg of 3: 1H NMR (300
MHz, CDCl3) δ 7.33 (1H, dd, J ) 8.0, 1.8 Hz, H-15′), 7.28 (1H,
dd, J ) 8.0, 2.2 Hz, H-14′), 6.72 (1H, s, H-9), 6.54 (1H, s, H-5′),
6.36 (1H, dd, J ) 8.2, 2.2 Hz, H-12′), 6.28 (1H, s, H-12), 6.22
(1H, dd, J ) 8.2, 1.8 Hz, H-11′), 5.99 (1H, s, H-8′), 3.92 (3H, s,
MeO-10), 3.74 (3H, s, MeO-3), 3.49 (3H, s, MeO-6′), 3.26 (3H,
s, MeO-2), 2.62 (3H, s, MeN-2′) and 2.33 (3H, s, AcO-4); NOED
δ 2.33 (AcO-4) relaxed to 3.74 (MeO-3, 0.5%).
P r ep a r a tion of Lon giber in e (1). Compound 9 (15 mg),
37% HCHO (0.5 mL) MeOH (0.8 mL), and conc HCl (0.3 mL)
were refluxed for 1 h, then HCHO (0.4 mL) and HCl (0.2 mL)
were added and refluxed for 1 h. H2O (20 mL) was added, then
NH4OH to pH 9 and extracted with CHCl3 (3 × 30 mL). The
CHCl3 phase yielded 11 mg of N′-norlongiberine, which was
immediately treated with HCHO (0.4 mL), HCO2H (0.4 mL),
and MeOH (0.5 mL) and refluxed for 1 h. The mixture was
evaporated under vacuum and the residue diluted with H2O
(20 mL), basified with NH4OH to pH 9.0, and extracted with
CHCl3 (3 × 30 mL). The CHCl3 residue was separated by
preparative TLC on Si gel (20 × 20 cm2, 0.75 mm) with
CHCl3-MeOH-NH4OH (92:8:1). The 4.5 mg of product showed
identical physical properties (TLC, IR, 1H NMR, [R]D, and CD)
with natural 1.
Meth yla tion of Lon giber in e (1). Longiberine (1) (41 mg)
in 5 mL of MeOH was treated with CH2N2 in Et2O prepared
from 1.5 g of Diazald (Aldrich) and 0.4 g of KOH. After 1 week,
the residue was passed through neutral Al2O3 (6 g) with CHCl3
and 1% MeOH in CHCl3 to give 40 mg of a pale yellow solid
identical (TLC, UV, [R]D, and 1H NMR) with 2 isolated from
the plant.
O-Eth yllon giber in e (4): Longiberine (1) (150 mg) in 5 mL
of MeOH was treated for 5 days with diazoethane in Et2O
prepared from 2 g of N-nitrosoethylurea and 5 mL of 50%
aqueous KOH. The mixture was chromatographed on Si gel
(50 g) with CHCl3 and 1% MeOH in CHCl3 to give 85 mg of 4:
1H NMR (90 MHz; CDCl3) δ 4.05 (2H, CH3CH2O) and 1.38 (3H,
CH3CH2O).
Na /NH3 Clea va ge of O-Eth yllon giber in e (4). O-Ethyl-
longiberine (4) (80 mg) in 6 mL of THF was reacted with Na
(180 mg) in liquid NH3 (20 mL) at -30 to -50 °C, and the
products separated as described.7 The nonphenolic fraction (14
mg) yielded unidentified products, and the phenolic fraction
(18 mg) after Si gel chromatography with CHCl3, 2% and 4%
Ack n ow led gm en t. We thank Dr. C. E. Cottrell for the
NMR spectra at 11.75 T and Mr. C. R. Weisenberger and Mr.
D. Chang for the mass spectra obtained at The Ohio State
University Chemical Instrument Center. The FT-NMR spec-

1414 J ournal of Natural Products, 1999, Vol. 62, No. 10
Lee et al.
(12) Ohashi, M.; Wilson, J . M.; Budzikiewicz, H.; Shamma, M.; Slusarchyk,
W. A.; Djerassi, C. J . Am. Chem. Soc. 1963, 85, 2807-2810.
(13) Marsaioli, A. J .; Ruveda, E. A.; Reis, F. de A. M. Phytochemistry 1978,
17, 1655-1658.
(14) Kametani, T.; Fukumoto, K.; Ihara, M.; Ujiie, A.; Koizumi, H. J . Org.
Chem. 1975, 40, 3280-3283.
(15) Thalidezine (6) and hernandezine (10) from T. longistylum are
documented in the Ph.D. dissertation of S.-S. Lee.
(16) Beecher, C. W. W.; Kelleher, W. J . In Alkaloids, Chemical and
Biological Perspectives; Pelletier, S. W., Ed.; J ohn Wiley and Sons:
New York, 1988; Vol. 6, Chapter 4, pp 297-337.
tra at 11.75 T (500 MHz) were obtained using equipment
funded in part by NIH Grant No. 1-510RR0145-01A1.
Refer en ces a n d Notes
(1) Alkaloids of Thalictrum 38. For part 37, see: Lee, S.-S.; Doskotch, R.
W. J . Nat. Prod. 1999, 62, 803-810. This study is taken in part from
the Ph.D. dissertation of S.-S. Lee as accepted by the Graduate School,
The Ohio State University, December, 1985.
(2) Bentley, K. W. The Isoquinoline Alkaloids; Harwood Academic:
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(18) Kametani, T.; Ihara, M.; Honda, T. Heterocycles 1976, 4, 483-526.
(19) Moore, M. L. In Organic Reactions; Adams, R., Ed.; J ohn Wiley and
Sons: New York, 1949; Vol. 5, Chapter 7, pp 301-330.
(20) Takao, N.; Iwasa K. Chem. Pharm. Bull. 1976, 24, 3185-3194.
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(22) Bohlmann, F. Chem. Ber. 1958, 91, 2157-2167.
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(25) Lee, S.-S.; Doskotch, R. W. J . Nat. Prod. 1996, 59, 738-743.
(26) Assigned by comparison to values for thalidezine (6) whose highfield
1H NMR spectrum was analyzed by extensive 1D and 2D NMR
studies given in the Ph.D. dissertation of S.-S. Lee.NP9902284
(5) Guinaudeau, H.; Leboeuf, M.; Cave´, A. J . Nat. Prod. 1988, 51, 1025-
1053 and previous summaries listed therein.
(6) Wu, W.-N.; Beal, J . L.; Doskotch, R. W. Tetrahedron Lett. 1976, 3687-
3690.
(7) Wu, W.-N.; Beal, J . L.; Leu, R.-p.; Doskotch, R. W. J . Nat. Prod. 1977,
40, 281-289.
(8) Moulis, C.; Stanislas, E.; Rossi, J .-C. Org. Magn. Reson. 1978, 11,
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(9) Patra, A.; Montgomery, C. T.; Freyer, A. J .; Guinaudeau, H.; Shamma,
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of Natural Products by Mass Spectroscopy, Vol. 1, Alkaloids: Holden-
Day: San Francisco, 1965; pp 173-175.
NP9902284