The document describes a proposed synthesis of the marine alkaloid aaptamine using benzyne-mediated cycloaddition of 1,2,4-triazines. Aaptamine and its derivatives possess biological activities. Previous syntheses of aaptamine were low-yielding and used difficult conditions. The proposed synthesis uses a mild fluoride displacement to generate reactive benzyne which undergoes inverse electron demand Diels-Alder reaction with tethered 1,2,4-triazines to form the necessary isoquinoline framework for aaptamine synthesis in three high-yielding steps.

1. TMS
OTf
CsF, ACN
80 C
N
R1
R3
R2
N
N
N
R1
R3
R2
N
N
N
R1
N
R1
COOH
NH2
isoamyl nitrite, toluene
R3
R2
R3
R2
COOH
NH2
O
O
COOH
N
O
O
N
Cl
isoamyl nitrite, HCl
1,2 DCE
80 C
N
R1
R3
R2
N
N
N
R1
R3
R2
N
HN
O
O
N
R1
R3
R2
N
N
N
R1
R3
R2
H2N CO2Et
N
H2N
N CO2Et
H2N CO2Et
S
H
H
O
O N
N
N
CO2Et
H
H
Benzyne-mediated Cycloaddition of 1,2,4-triazines in the
Synthesis of Aaptamine
May Young, Tyler Casselman, Cuifang Cai, Kyle Strom, John K. Snyder
Boston University, Chemistry Department
The aaptamines are marine alkaloids1 with a benzo[de][1,6]naphthyridine framework isolated from marine sponges in the genera Aaptos and Suberites1 with members such as aaptamine, 9-demethylaaptamine, bisdemethylaaptamine, isoaaptamine, 9-
demethyloxyaaptamin, and 4-N-methylaaptamine. Aaptamine and isoaaptamine, both isolated from Aaptos aaptos, possess α-adrenoreceptor blocking activity on vascular smooth muscle as well as cytotoxicity against P-388, KB16, A549, and HT-29
tumor cells2. Previous syntheses of the aaptamines use either isoquinoline or quinoline components of the benzo[de][1,6]naphthyridine ring1, resulting in low yields, usage of uncommon reagents, difficult reaction conditions, and the production of
undesired side products. A simple three-step synthesis of aaptamine is proposed using inverse electron demand Diels-Alder chemistry in the intermolecular cycloaddition of benzyne with tethered 1,2,4-triazines to afford the isoquinolines necessary in
the synthesis of aaptamine.
N
Z
X
Y
N
N
R1
R2
N
Z
X
Y
R1
R2
+
Z = SMe, Cl
CH3CH2NO2
Pd(TFA)2, AgOAc (4 eq)
N
X
Y
R1
R2
O2N
OL 2013, 15, 1718
(EtO)3P, 120 oC
N
X
Y
R1
R2
HN
Chem Commun. 1987, 150
For Aaptamine, X = Y = OMe
Background
Synthesis Scheme
Benzyne-Mediated Diels Alder
Aryl Triflate Benzyne Generation
Arenediazonium-2-Carboxylate as a
Benzyne Precursor
2-Carboxy-4,5-Dimethoxy Benzenediazonium
Chloride as a Benzyne Precursor
Future Work
Works Cited
Acknowledgements
• Fluoride displacement of trimethylsilyl group allows benzyne
generation under mild conditions
• Determine generation of 2-carboxy-4,5-dimethoxy
benzenediazonium chloride through use in a known literature
• Aaptamine, an alkaloid isolated from Aaptos aaptos
• Aaptamine family are marine alkaloids isolated from Aaptos
and Suberites
• Works as well as aryl triflate benzyne generation
• Drawback is explosive nature of diazonium compounds
• Generated under much harsher conditions
• HOMO/LUMO of benzyne
• Work on HOMO for triazine – cannot lower LUMO further
with dihydrogen
Dr. John K. Snyder Tyler Casselman
Kyle Strom Boston University CIC
Cuifang Cai Boston University CMLD
Karen Noguera
1. Larghi, E.L.; Obrist, B.V.; Kaufman, T.S. A Formal Total
Synthesis of the Marine Alkaloid Aaptamine. Tetrahedron. 2008,
64, 5236 – 5245.
2. Shen, Y.C.; Lin, T.T.; Sheu, J.H., Duh C.Y. Structures and
Cytotoxicity Relationship of Isoaaptamine and Aaptamine
Derivatives. J. Nat. Prod. 1999, 62, 1264 – 1267.
3. Longley, R.E.; McConnell, O.J.; Essich, E.; Harmody D.
Evaluation of Marine Sponge Metabolites for Cytotoxicity and
Signal Transduction Activity. J. Nat. Prod. 1993, 56, 915 – 920.
4. Bassoli, A.; Maddinelli, G.; Rindone, B.; Tollari, S.; Chioccara,
F. A Simple Synthesis of Aaptamine, a 1H-benzo[de][1,6]-
naphthydine alkaloid. J. Chem. Soc., Chem. Commun. 1987, 150
– 151.
5. Zhang, M.; Hu, P.; Zhou, J.; Wu, G.; Huang S.; Su, W. Pd-
Catalyzed Multidehydrogenative Cross-Coupling between
(Hetero)Arenes and Nitroethan to Construct β-Aryl
Nitroethylenes. Organic Letters. 2013, 15(7), 1718 – 1721.
R1N
N
R2O
OMe
Aaptamine (1): R1= H,R2 = Me
Isoaaptamine (2): R1= Me, R2 = H
N
N
O
OMe
3
IC5's µg/mL
• Arynes or benzyne have a strained triple bond, making it highly
reactive
• Participates in inverse electron demand Diels Alder as
dienophile
• Benzo[de][1,6]naphthyridine framework
• Derivatives and other members include:
isoaaptamine,
demethoxy(loxy)aaptamine, 9-
demethylaaptamine, 4-methylaaptamine,
etc.
• Possess α-adrenoreceptor
blocking activity on vascular
smooth muscle and
cytotoxicity against numerous
cancer cell lines
• Previous synthesis
complicated, low yields
• Simple 3-step synthesis
proposed