J. Org. C h e m . 1992,57,2774-2783
2774
Articles Synthesis of Putative Intermediates in the Biosynthesis of the Kinamycin Antibiotics: Total Synthesis of Phenanthroviridin Aglycon and Related Compounds Makarand P. Gore, Steven J. Gould,* and Dwight D. Weller Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003
Received November 5 , 1 9 9 1
Phenanthroviridin aglycon, 14, recently isolated from Streptomyces viridiochromogenes DSM 3972, and the correspondingpyridone 10 have been synthesized from the common intermediate (bromoary1)naphthamide42. This was prepared by condensation of a (trimethylsily1)ethyl(bromoary1)cinnamate36 and a methoxy-substituted cyanophthalide anion 15, providing the ABD rings of the target benzo[b]phenanthridineskeleton. The aglycon 14 was obtained by a sequence of metal-halogen exchange and formylation,Hofmann rearrangement, cyclization, and deprotection. The pyridone was obtained by Hofmann rearrangement, metal-halogen exchange, cyclization, and deprotection. In addition, a route to cinnamate 36 via coumarin 49 was developed which would allow selective protection of the 1-hydroxylgroup for synthesis of glycosidic analogues of phenanthroviridin, 13. The methodology developed is useful for preparation of 10, 14, and analogues specificallylabeled at C-5 for study of biosynthesis of the kinamycin antibiotics. The kinamycin antibiotics (cf. kinamycin D, 1) were isolated from Streptomyces murayamaemis and characterized by Omura and co-~orkers.l-~These compounds are active against Gram-positive and-to a lesser degree-Gram-negative organisms. Antitumor activity is exhibited by kinamycin C against Ehrlich ascites carcinoma and against sarcoma-180.2 We have previously isolated four additional active metabolites: kinamycin E, 2, kinamycin F, 3, prekinamycin, 4, and ketoanhydrokinamycin, 5, from the same organism? Recently, 3-0-isobutrylkinamycin C, 6, and 4-deacetyl-4-0-isobutrylkinamycin C, 7, which are active against Grampositive bacteria, L1210 leukemia, IMC carcinoma, LX-1 human lung carcinoma, and SC-6 human stomach carcinoma were isolated from a Saccharothrix specie^.^ The remarkable benzo[ b]tetrahydrocarbazole skeleton and cyanamide moiety are unique to this group of metabolites.
HO
0
Rl
R2
R3
R4
1
Ac
2 3 6 7
H H
Ac Ac H
H H H
Ac
H H H COCbu
H
H
COkbu
H
H
H
(1)Ito, S.;Matsuya, T.; Otani, M.; Nakagawa, A.; Iwai, Y.; Ohtani, M.; Hate, T. J. Antibiot. 1970,23,315-317. (2)Hata, S.; Omura, S.; Iwai, Y.; Nakagawa, A.; Otani, M. J.Antibiot. 1971,24,353-359. (3)Omura, S.; Nakegawa, A.; Yamada, H.; Hata, T.; Furusaki, A,; Watanabe, T. Chem. Pharm. Bull. 1973,21,931-940. (4)Seeton, P. J.; Gould, S. J. J. Antibiot. 1989,42,189-197. (5)Ieshiki, K.;Sawa, T.; Nakagewa, H.; Matsuda, N.; Hattori, S.; Hamada, M.; Takeuchi, T.; Ooeono, M.; Ishizuka, M.; Yang, Z.; Zhu, B.; XU, W. J. Antibiot. 1989,42,467-469.
Previous investigations in our laboratory have established that the kinamycins are of polyketide origin, apparently derived from a decaketide 8,6,’ with the biosynthesis of the benzo[b]carbazole skeleton of the kinamycin antibiotics proceeding via the benzo[a]anthraquinone g7 (Figure 1). It appears that 9 undergoes an unusual oxidation/nitrogen insertion/ring contraction process leading to the formation of the N-cyanobenu>[b]carbaole skeleton to give prekinamycin, 4, by excision of C-5 and C-6 in which C-6 is lost and C-5 ends up in the cyanamide moiety? We had predicted that the hypothetical pyridone 10,which could be formed by oxidationa of 9 via a diacid intermediate 11 and/or the acid aldehyde intermediate 12, might be an intermediate in this remarkable transformation6 although naturally occurring compounds which have the benzo[b]phenanthridine skeleton were unknown at that time. However, the isolation of the first naturally occuring benzo[b]phenanthridine, phenanthroviridin, 13, and ita aglycon, 14,from S. uiridiochromgenes DSM 3972 has recently been r e p ~ r t e d .Both ~ compounds are active against lung carcinoma MBA9812 in mice. It seemed quite reasonable to also consider 14 as a potential intermediate in the formation of the benzo[b]carbazole skeleton, and a reasonable modification of the biosynthetic proposal which includes 14 is shown in Figure 1. The need for compounds with strategically placed isotopic labels for biosynthetic studies and the lack of useful methods of synthesis of the potentially therapeutic ben~~[blphenanthridines prompted us to initiate a program to develop a divergent methodology for the preparation of compounds 9-14. We have recently reported part of these studies leading to the total synthesis of phenanthroviridin aglycon 14.1° This article describes the details (6) Seaton, P. J.; Gould, S. J. J. Am. Chem. SOC.1988,110,5912-5914. (7)Seaton, P. J.; Gould, S. J. J. Am. Chem. SOC.1987,109,5282-5284. (8)For related biological oxidations see ref 30 in ref 7. (9)Fendrich, G.; Zimmermann, W.; Gruner, J.; Auden, J. A. L. Eur. Pat. Appl. EP 304,400(CI.C07D221/18),22 Feb 1989,CH Appl. 87/3, 196, 20 Aug 1987,13 pages; Chem. Abstr. 1990,112,75295q. (IO) Gore, M. P.; Gould, S. J.; Weller, D.D. J. Org. Chem. 1991.56, 2289-2291.
0022-3263/92/1957-2774$03.oO/00 1992 American Chemical Society
J. Org. Chem., Vol. 57, No. 10,1992 2775
Kinamycin Antibiotics
9
CH~C-SCOA7 COOH
HO 0
9
8
*-
d
-
0
HO
10
H
'
/ I
-c
HO
0
"CN
3
"'OH H3
\
0
HO
0
I
HO
5
4
MeHN H
& -14. R =
I
I
' $'OAc
N'*CN
0 1
Figure 1. Biosynthesis of kinamycin D in S. murayamaensis. Scheme I'
Scheme 11"
CHO 21
OH
16, R = COOCH, 18, R I NO?
17
a
-c
I
IC
b
~o OCH3 15
H3CO
6
19, R = COOCH3 (70 %) 20, R = NO2 (45 %)
H3C0
0
21, R = COOH 22, R OH
23
KOH/HzO/THF.
of the divergent methodology developed for the total synthesis of 10 and 14 and analogues, along with some of the potentially biologically important aspects of the chemistry of these compounds that were discovered during these studies.
Results and Discussion In order to obtain the angular tetracyclic ring system, we envisioned that the ABD rings could be constructed via coupling of a cyanophthalide with a substituted cinnamate or nitrostyrene." This would allow specific introduction of isotopic labels at C-5 (and nitrogen at position 6 in the case of 10 and 14)near the end of the synthesis. Readily available cyanophthalide 15,which has the required substitution, was used for the synthesis.12 Initially the desired cinnamate 16 was prepared in good yield from aldehyde 1713by Knoevenagel c~ndensation'~ with malonic acid to give the corresponding cinnamic acid followed by esterification with diazomethane (Scheme I). (11) For use of cyanophthalidefor synthesis of linear tetracycles see refs 5-8 in ref 10. (12) Li, T.; Wu, Y. L. J.Am. Chem. SOC.1981,103,7009-7011. (13) Hauser, F. M.; Ellenberger, S. R. Synthesis 1987, 723-724. (14) Jones, G. Org. React. 1967,15,204-599.
22
'Key: (a) OH-; (b) NH,; (c) air (02).
Key: (a) K2S208,Cuz-; (b) malonic acid/py/piperidine; (c) CH2N2; (d) CH3NOz/bitylamine; (e) LDA then 16 or 18; (0 a
Later, conditions were found for successful ~ondensation'~ with nitromethane to yield the nitrostyrene 18. Consensation of 16 and 18 with the anion of the cyanophthalide1°J2 15 followed by oxidative workup gave the corresponding quinones 19 and 2016 in 70% and 45% yields, respectively. Treatment of 19 with potassium hydroxide in methanol yielded a mixture of two acidic products, which were soluble in NaHC03 and were reprecipitated by aqueous HC1. One of the products (43%) was the desired acid 21. The other was shown to be the hydroxyquinone 22 (44%). The mass spectrum of 22 had a molecular ion at mlz 324 (go%), and there was no acid or ester carbonyl resonance in the 13C NMR spectrum." The conversion of 21 to 22 can be explained by the mechanism shown in Scheme 11. The formation of 22 seemed analogous to the biogenesis proposed for 10 and 14 (Figure 2), in this case with hydroxyl as the nucleophile. Therefore, acid 21 was treated ~
(15) Scha!es, 0.;Graete, H. A. J.Am. Chem. SOC.1952,74,4486-4490. (16) Studies to prepare 4 using 20 are in progress.
(17) Assignment of the structure 22 was confirmed by preparation of the corresponding ethoxycarbonylatedderivative. The authentic pure acid 21 could be obtained in good yield by treatment of the tert-butyl analogue of 19 with sulfuric acid, or by recrystallization,but the overall yields were low due to lower (-40%) yield in the phthalide cyclization reaction.
2776 J. Org. Chem., Vol. 57, No.10, 1992
Gore et al. Scheme IVa Br
Br
I
14
33
32
.I
NH
3-
10
HO 0
HO OH
Br R=H,34;R=Me, 35 R = TMSE, 36
T K E=
"Key:
lio 0 ) 4 Figure 2. Possible biogenesis of 4 from 14: the naphthoquinone aa a "2-proton, 4-electron sink". Scheme 111"
fl H3
' 0
H,CO
H,CO
19
COOCH, 6CH3 24 (88%)
c,d COOH H3C0
OCH,
H,Ch
bCH3
25 (95%)
26 (93%)
H3C0 H ~ CI O W
-
H
3
I
H3C0
OCH,
NHCOOCH:,
H,Ch
b
270 "C dec; IR (KBr) 3336,1681, 1653, 1583, 1479, 1338, 1285, 1246, 1123, 1015 cm-'; 'H NMR (CDC13)6 9.43 (br s, 1H), 7.89 (d, J = 1Hz, 1 H), 7.72 (m, 2 H), 7.27-7.24 (m, 1H), 7.13 (d, J = 1Hz, 1 H), 4.05 (s,3 H), 3.97 (s, 3 H), 2.53 ( ~ , H); 3 13CNMR (CDCl3) 6 181.2, 176.2, 161.0,160.0, 157.6, 142.4, 137.9, 136.4, 135.4, 129.9, 120.0, 119.9, 119.5, 118.0, 117.6, 117.5, 116.4, 56.6, 56.4, 22.0; MS m / e 349.1 (100); HRMS calcd for C d 1 6 N 0 5349.0950, found 349.0949. 3-Methyl-GH-benzo[b]phenanthrido-'l,l2-quin-5-one, 10. A solution of BBr3 (0.1 mL, 1.0 M in CH2C12,0.1 mmol) was added to a solution of 51 (0.004 g, 0.01 mmol) in CHzClz(1mL) at -78 "C, and the mixture was warmed to room temperature and stirred for 1h. Ethylene dichloride (1mL) was added, and the mixture was sonicated for 3 h and then stirred for 23 h. Methanol (3 X 3 mL) was added, and the solution waa concentrated (3 X) to ca. 2 mL by boiling. The solvent was then completely evaporated, and the residue was dissolved in 1M aqueous NaOH. Acidification to pH 2.0 using concd HC1, extraction with CHCl, (3 X 5 mL), drying of the organic layers, and concentration gave purple crystalline 1015(0.003 g, -81% yield): mp >265 OC; IR (KBr) 3475,3276,1684,1638,1463cm-'; 'H NMR (D20,NaOD) 6 7.40 (t,J = 8 Hz, 1H), 7.17 (8, 1H), 7.06 (d, J = 8 Hz, 1H), 6.89 (d, J = 8 Hz, 1H), 6.72 (s, 1H), 2.38 (s,3 H);13CNMR (CF3COOD, CDCl3) 6 186.3,180.6,163.2,161.9,154.8, 145.3,138.8,132.7,127.9, 126.4, 125.9, 123.1, 122.2, 119.2, 118.2, 21.3; FAB HRMS calcd for C18H12N05 322.0720, found 322.0720 (MH+). 2-Bromo-6-hydroxy-4-methylbenzaldehyde, 50. Boron tribromide (1.0 mL, 1.0 M in CH2C12,1.00 mmol) was added to a solution of the aldehyde 30 (0.229 g, 1.00 mmol) in CH2C12(3 mL) cooled to -78 "C. The mixture was stirred for 15 min at -78 "C and 1h at room temperature. The mixture was then poured cautiously onto ice-water (5 mL) and saturated aqueous NaHC03 (5 mL) and was stirred for 15 min. Extraction with EtOAc (3 X 10 mL), drying of the organic layers, and concentration gave a pink oil. Flash chromatography (1.5 X 17.5 cm, 25% CH2C12/hexane)gave rhombic colorless plates of 50 (0.190 g, 88%): mp 53-54 "C; IR (KBr) 2800,1650,1561,1514,1388,1303,1211, 1183, 774 cm-'; 'H NMR (CDC13)15 12.00 (8, 1H), 10.24 (8, 1H), 6.99 (d, J = 1Hz, 1H), 6.74 (br s, 1H), 2.34 (8, 3 H); 13CNMR (CDC13) 6 196.9, 163.7, 149.6, 127.1, 125.5, 117.8, 115.6, 21.8; MS m / e 213.9 (711,215.9 (30). Anal. Calcd for C8H7Br02: C, 44.68, H, 3.28; Br, 37.15. Found C, 44.65; H, 3.13; Br, 37.13. 5-Bromo-7-methylcoumarin, 49. A solution of salicylaldehyde 50 (0.130 g, 0.60 mmol) and freshly fused potassium acetate (0.035 g, 0.35 mmol) in acetic anhydride (0.5 mL, xs) was heated at reflux (bath temperature 150-160 "C) for 5 h. The mixture was cooled to -100 "C and poured into water (10 mL) and then extracted with EtOAc (3 X 10 mL). The organic layers were washed with saturated aqueous NaHC03 (10 mL) and dried. Evaporation gave a yellowish solid which was purified by flash chromatography (1.5 (45) Phenanthridone 10 is only sparingly soluble in most of the solvents including DMSO. We believe that two of the carbon resonances in the aromatic region are not visible due to overlap with the solvent (CF,COOD) signals.
15 cm, CH2C12)to give white needles (0.136 g, 94%) of 49 mp 140-141 "C; IR (KBr) 1750,1739,1726,1610,1201,1139,1108, 855, 843 cm-'; 'H NMR (CDC1,) b 7.96 (d, J = 9 Hz, 1 H), 7.30 (br 8, 1H), 7.04 (d, J = 1 Hz, 1HI, 6.39 (d, J = 9 Hz, 1H), 2.42 (s,3 H); '3c NMR (CDC13)6 160.0,154.4,143.7,141.9,129.2,121.7, 116.5, 116.3, 116.2, 21.3; MS m / e 237.9 (72), 239.9 (81). Anal. Calcd for C1&I7BIo2: C, 50.24, H, 2.95; Br, 33.42. Found: C, 49.89; H, 2.98; Br, 33.45. 2-(Trimethylsily1)ethyl 2-Bromo-4-methyl-6-hydroxycinnamate, 51. A solution of butyllithium (1.50 mL, 1.41 M in hexanes, 2.11 mmol) was added to a solution of 2-(trimethylsilyl)ethanol(O.35mL, 2.44 mmol) in dry THF (4 mL) at -78 "C, and the solution was warmed to room temperature and stirred for 15 min. A solution of coumarin 49 (0.478 g, 2.00 mmol) in dry THF (4 mL) was added at -78 OC, and the mixtwe was heated at reflux for 2 h. The reaction was quenched using acetic acid (0.2 mL, xs), and the solvent was evaporated. Extraction with ether (3 X 10 mL), drying, and evaporation of the ether layers gave a yellow solid. Flash chromatography (2 X 20 cm, 18% EtOAc/hexane) gave 0.699 (72% yield) of white crystalline 51: mp 145-147 "C; IR (KBr) 3234,3226,3212,1685,1675,1603,1565, 1380,1317,1285,1203cm-'; 'H NMR (CDC13)6 8.81 (br s, 1H), 7.93 (d, J = 16 Hz, 1 H), 7.07 (d, J = 16 Hz, 1H), 6.90 (s, 1H), 6.61 (8, 1H), 4.28 (br t, 3 H), 2.15 (s, 3 H), 1.02 (br t, 2 H), 0.00 (a, 9 H); '3c NMR (CDCl,) 6 170.2,157.6,142.2,141.2,127.0,125.7, 121.9, 118.3, 116.5, 63.5, 21.0, 17.3, -1.4; CIMS (CHI) m / e 359 (18), 357 (18), 315 (98), 313 (100). And. Cdcd for Cl6HZ1Bfi3Sk C, 50.42, H, 5.92; Br, 22.36. Found C, 50.43; H, 5.90; Br, 22.32. X
Acknowledgment. This work was supported by US. Public Health Service Grant GM 31715 t o S.J.G. Dr. Gabriele Fendrich, Ciba-Geigy Pharma Biotechnology, Basel, Switzerland, is thanked for an authentic sample of phenanthroviridin aglycon and data for its spectroscopic characterization. The multinuclear Bruker AC 300 NMR spectrometer was purchased through grants from the Public Health Service Division of Research Resources (RR04039-01) and the National Science Foundation (CHE-8712343) to Oregon State University. The multinuclear Bruker AM 400 NMR spectrometer was purchased in part through grants from the National Science Foundation (CHE-8216190) and from the M.J. Murdock Charitable Trust to Oregon State University. Registry NO.LO, 137057-04-6; 14,124903-84-0;15,81060-27-7; 16,139976-02-6;17,57415-35-7;18,139976-03-7;19,139976-04-8; 20,139976-05-9; 21,139976-06-0; 22,139976-07-1; 23,139976-082; 24,139976-09-3;25,139976-10-6; 26,139976-11-7; 27,133129-381; 28,139976-12-8;29,139976-13-9;30,133129-29-0; 31,72623-20-2; 32,72638-60-9; 33,78998-97-7; 34,139976-14-0;35,139976-15-1; 36,139976-16-2;37,139976-17-3; 38,133129-31-4; 39,139976-18-4; 40,140110-69-6;42,133129-33-6; 43,133129-34-7; 44,133129-37-0; 45,133129-39-2;46,139976-23-1; 47,139976-24-2; 48,139976-19-5; 49,139976-20-8; 50,139976-21-9; 41,133129-36-9; malonic acid, 141-82-2;2-methoxy-4-methylcinamicacid, 53005-58-6; 2,5dimethylphenol, 95-87-4; kinamycin, 131439-64-0. Supplementary Material Available: 'H and 13C NMR spectra of selected compounds (38 pages). This material is contained in many libraries on microfiche, immediately follows this article in the microfilm version of the journal, and can be ordered from the ACS; see any current masthead page for ordering information.
