Synthesis of 7,8-disubstituted benzolactam-V8 and its binding to protein kinase C

Article abstract of DOI:10.1016/S0960-894X(00)00609-0

7-methoxy-8-decynyl-benzolactam-V8 4 is synthesized using a catalytic asymmetric alkylation reaction as a key step. This compound shows potent activity to three PKC isozymes tested (K_i = 45.6, 91.1, and 121.3 nM to PKCα, δ, and ε, respectively), indicating that introduction of a suitable substituent at the 7-position of 8-decynyl-benzolactam-V8 only slightly reduces the PKC binding affinity.

Full text of DOI:10.1016/S0960-894X(00)00609-0

Bioorganic & Medicinal Chemistry Letters 11 (2001) 99±101
Synthesis of 7,8-Disubstituted Benzolactam-V8 and Its Binding to
Protein Kinase C
Dawei Ma,a,* Tao Zhang,a Guoqiang Wang,a Alan P. Kozikowski,b,*
Nancy E. Lewinc and Peter M. Blumbergc
aState Key Laboratory of Bio-organic and Natural Product Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China
bDrug Discovery Laboratory, Institute for Cognitive & Computational Sciences, Georgetown University Medical Center,
3970 Reservoir Road, N.W., Washington, DC 20007-2197, USA
cNational Cancer Institute, Bethesda, MD 20892, USA
Received 21 August 2000; accepted 12 October 2000
AbstractÐ7-Methoxy-8-decynyl-benzolactam-V8 4 is synthesized using a catalytic asymmetric alkylation reaction as a key step.
This compound shows potent activity to three PKC isozymes tested (Ki=45.6, 91.1, and 121.3 nM to PKCa, d, and e, respectively),
indicating that introduction of a suitable substituent at the 7-position of 8-decynyl-benzolactam-V8 only slightly reduces the PKC
binding anity. # 2001 Elsevier Science Ltd. All rights reserved.
PKCs are a growing family of isozymes involved in a
wide variety of cellular processes.1 Marked di€erences
in tissue distribution and substrate speci®cities have
suggested that these isozymes may play the di€erent
roles in physiological and pathophysiological pro-
cesses.1,2 The isozyme-speci®c modulators are highly
required in identifying these di€erent roles, especially in
vivo.1,2 However, although several isozyme-selective
inhibitors for PKCs have been developed in recent
years,3-6 few isozyme-selective activators have been
reported up to now.7 The teleocidins are a class of nat-
ural products that were found to have potent activity
for PKCs but with little selectivity.8 Endo and co-
workers reported that benzolactam-V8 1a (Fig. 1), a
twist-like conformation mimic of indolactam is still a
potent activator to PKCs.9 We felt that this compound
is a good lead compound for developing isozyme-selec-
tive activators owing to its simplicity. In a previous
report,10 we have mentioned that if an acetylene chain is
placed at the 8-position of benzolactam-V8, the gener-
ated compound 2a had improved isozyme-selectivity in
either activation or down-regulation to PKCs, while ana-
logue 2b with a saturated chain at the 8-position of benzo-
lactam-V8 did not show marked isoform-selectivity.
Further studies have shown that 2a had marked anti-
proliferative activity against two breast carcinoma cell
lines. These results implied that the substituted groups
at the aromatic ring of the benzolactam-V8s might play
some roles to their isoform-selectivity. Encouraged by
these results, we designed two new analogues 3 and 4, in
which a methoxy group was introduced at the 7-position
*Corresponding author. Tel.: +86-21-64163300; fax: +86-21-
64163300; e-mail: madw@pub.sioc.ac.cn
Figure 1. Structures of teleocidin family and benzolactam-V8 analogues.
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00609-0

100
D. Ma et al. / Bioorg. Med. Chem. Lett. 11 (2001) 99±101
of 1a and 2a, respectively, in order to check if a 7-sub-
stituted group could change the activity or selectivity of
this class of compounds to PKCs.
which was hydrolyzed with hydrochloric acid to pro-
duce the desired amino ester 8. In our laboratory, this
reaction was carried out in a scale of more than 20 g and
therefore proven to be a very practical procedure.
Because it was not easy to determine the enantiomeric
purity of the resultant a-amino acid derivative and the
absolute con®guration of the major enantiomer at this
stage, we planned to solve this problem by transforming
8 into the target molecules. Thus, N-protection of 8 with
Boc and reduction of ester with lithium borohydride
a€orded alcohol 9. Hydrogenation of 9 catalyzed by Pd/
C released amine 10, which was coupled with d-valine-
derived tri¯ate 11 to a€ord the substitution product 12.
After hydrolysis of 12 with 2 N NaOH, the generated
acid 13 was cyclized via the activated ester approach9,10
to give two lactams, which were subjected to reductive
methylation to provide separable 3 and 14 in a ratio of
3/1. By this result we concluded that the ee value of the
asymmetric alkylation step (from 7 to 8) was about
75%. The stereochemistry of 313 and 1413 was con-
®rmed by comparing their spectra with (2S,5S)- and
(2S,5R)-benzolactam-V8s.10,11 Therefore, we concluded
that the con®guration of the major enantiomer in step
alkylation should be S, which is consistent with Lygo's
report.12 In addition, by NOE studies and comparison
of the chemical shifts of 3 with those of (2S,5S)-benzo-
lactam-V8, it was found that compound 3 displayed the
twist-conformation in solution. It was notable that if the
cyclization method mediated by DPPA in the transfor-
mation of 12 to 3 was used, a quite lower yield (23%
yield) was obtained. This result gave an additional
example to demonstrate that the activated ester
approach was a general method for synthesizing this class
of lactams although the DPPA method gave a high yield in
some cases.14 Finally, iodination of 3 assisted by mercur-
y(II) chloride followed by palladium-catalyzed coupling
reaction with 1-decyne produced 415 in 75% yield.
Our synthesis for 3 and 4 is outlined in Scheme 1. 5-
Nitro-1,3-benzodioxane 5, prepared from 3-nitrophenol
according to the known procedure11 with an improved
yield, was re¯uxed in 1 N HCl for 48 h to provide alco-
hol 6 (87% yield based on about 30% starting material
recovery). Methylation of phenol 6 with iodomethane
under the assistance of K2CO3 followed by bromination
of the primary alcohol a€orded bromide 7. Next, we
tried to use a newly reported method to introduce the
chiral phenylalanine moiety.12 As a result, treatment of
7 with Schi€ base derived from tert-butyl glycinate12
under asymmetric phase transfer condition (catalyst:
cinchonidine-derived salt 15) gave the coupling product,
Compounds 3 and 4 have been evaluated for their abil-
ity to displace phorbol 12,13-dibutyrate (PDBU) bind-
ing from recombinant PKCa.5a Ki values for 3, 4,
benzolactam-V8 and 8-decynyl benzolactam-V8 were
7162, 45.6, 334 and 15 nM, respectively. This meant that
4 was 3-fold less potent than 8-decynyl benzolactam-V8,
while 3 was 22-fold less potent than benzolactam-V8. It
indicated that introduction of a suitable substituent at
the 7-position of 8-decynyl benzolactam-V8 only
slightly reduced its activity. In addition, compound 4
was found to have potent binding anities to PKCd
and e (Ki=91.1 and 121.3 nM, respectively), which
implied that this analogue had similar but poorer iso-
form-selectivity in comparison with 8-decynyl-benzo-
lactam-V8. Further development of more analogues
using this methodology, as well as their isoform-selec-
tivity studies are in progress.
Acknowledgements
The authors are grateful to the Chinese Academy of
Sciences, National Natural Science Foundation of China
(Project 29725205) and the NIHAU (CA79601) for their
®nancial support.
Scheme 1.

D. Ma et al. / Bioorg. Med. Chem. Lett. 11 (2001) 99±101
101
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(300 MHz, CDCl3) d 7.11 (t, J=8.1 Hz, 1H), 6.77 (br s, 1H),
6.65 (d, J=8.1 Hz, 1H), 6.48 (d, J=8.2 Hz, 1H), 3.82 (s, 3H),
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