Isao Kubo



Research Interests

Natural products chemistry

Research Description

Our group has been searching for ecologically sound pest control agents based on natural products (including biopolymers such as enzymes) that fundamentally regulate nature. Our studies have focused on developing alternative insect control agents, but the scope has now extended to microorganisms and weeds.

Current Projects

A number of biologically active natural products have been isolated but only a few are useful to us as pest control agents. This is mainly due to the lack of their rational exploration, even though understanding their effects on biological systems and the biochemical changes involved are known to be essential. For example, plant resistance to pests usually involves combinations of compounds, many of them short-lived. Their dynamic analysis and functional understanding are needed. Our group has been pursuing this type of study.

Based on our observation during a simple lettuce seedling assay, we found that the lettuce exuded a polyphenol oxidase (PPO) from the roots of the seedlings into the rhizosphere. This can be visualized when an exogenous substrate such as catechin is present in the test solution, the root caps and solution surrounding the roots are stained yellow to orange. Thus, the enzyme exuded from the root of lettuce seedlings oxidizes catechin although the corresponding o-quinone has not yet been characterized. In addition to lettuce, a number of crops such as tomato, alfalfa, corn and wheat also exude PPOs that are membrane-bound copper containing glycoproteins. The role of the PPO exuded from lettuce seedling, as well as other plants, may be a line of passive defense against soil microorganisms and insects. This led us to investigate the role of PPO, using a series of simple phenolic compounds as a model in order to gain new insights into their actions on a molecular basis. The enzyme has been isolated from the lettuce exudate and its structural characterization is underway. This study has been extended to a similar oxidase present in insects known as tyrosinase because it is one of the key enzymes in the insect molting process. We have reported that ecdysteroid-22-O-acyltransferase in the tobacco budworm, Heliothis virescens plays an important role as a line of defense against exogenous ecdysteroids. Accumulation of this kind of knowledge may provide clues to design more appropriate pesticides.

Another aspect of our research is identifying the antimicrobial activity of natural products. This ongoing project has begun to encompass the underlying rationale for structure-antimicrobial activity relationships.

Selected Publications

Synergistic effects of anacardic acids and methicillin against methicillin-resistant Staphylococcus aureus. [H. Muroi, K. Nihei, K. Tsujimoto and I. Kubo. (2004) Bioorg. Med. Chem. 12, 583-587].

2-Hydroxy-4-isopropylbenzaldehyde, a potent partial tyrosinase inhibitor. [K. Nihei, Y. Yamagiwa, T. Kamikawa and I. Kubo. Bioorg. Med. Chem. Lett. (2004) 14, 681-683].

Hydroquinone, a control agent of agglutination and adherence of Streptococcus mutans induced by sucrose. [M. Himejima, K. Nihei and I. Kubo. (2004) Bioorg. Med. Chem. 12, 921-925].

Characterization of xanthine oxidase inhibition by anacardic acids. [N. Masuoka and I. Kubo. (2004) Biochim. Biophys. Acta 1688, 245-249].

Structural criteria for depigmenting mechanism of arbutin. [I. Hori, K. Nihei and I. Kubo. (2004) Phytother. Res. 18, 475-479].

Arudonine, an allelopathic steroidal glycoalkaloid from the root bark of Solanum arundo Mattei. [K. Fukuhara, K. Shimizu and I. Kubo. (2004) Phytochemistry 65, 1283-1286].

Molecular design of multifunctional food additives: Antioxidative antifungal agents. [K. Nihei, A. Nihei and I. Kubo. (2004) J. Agric. Food Chem. 52, 5011-5020].

Oxidation products of quercetin by mushroom tyrosinase. [I. Kubo, K. Nihei and K. Shimizu. (2004) Bioorg. Med. Chem. 12, 5343-5347].

Methyl-p-coumarate, a melanin formation inhibitor in B16 mouse melanoma cells. [I. Kubo, K. Nihei and K. Tsujimoto. (2004) Bioorg. Med. Chem. 12, 5349-5354].

Pachyelasides A, B, C, and D; Novel molluscicidal triterpene saponins from Pachyelasma tessmannii. [K. Nihei, B-P Ying, H. Murakami, N. Matsuda, M. Hashimoto, and I. Kubo. (2005) J. Agric. Food Chem. 53, 608-613].

Insect antifeedants from tropical plants: Structures of zumsen, zumsenin and zumsenol. [K. Nihei, Y. Asaka, Y. Mine and I. Kubo. (2005) J. Nat. Prod. 68, 244-247].

Lipoxygenase inhibitory activity of anacardic acids. [T. J. Ha and I. Kubo. (2005) J. Agric. Food Chem. 53, 4350-4354].

Naturally occurring antifungal agents against Zygosaccharomyces bailii and their synergism. [K. Fujita and I. Kubo. (2005) J. Agric. Food Chem. 53, 5187-5191].

Multifunctional action of antifungal polygodial against Saccharomyces cerevisiae: Involvement of pyrrole formation on cell surface in antifungal action. [K. Fujita and I. Kubo. (2005) Bioorg. Med. Chem. 13, 6742-6747].

Antioxidant activity of anacardic acids. [I. Kubo, N. Masuoka, T. J. Ha and K. Tsujimoto. (2006) Food Chem. 99, 555-562.

Mani├žoba, a quercetin-rich Amazonian dish. [I. Kubo, N. Masuoka, K. Nihei and B. Burgheim. (2006) J. Food Composit. Anal. 19, 579-588].

Musidunin and musiduol, insect antifeedants from Croton jatrophoides. [K. Nihei, Y. Asaka, Y. Mine, Y. Ymada, M. Iigo, T. Yanagisawa and I. Kubo. (2006) J. Nat. Prod. 69, 975-977].

Anethole, a potential antimicrobial synergist, converts a fungistatic dodecanol to a fungicidal agent. [K. Fujita, T. Fujita and I. Kubo. (2007) Phytother. Res. 21, 47-51].

Slow-binding inhibition of soybean lipoxygenase-1 by dodecyl gallate. [T. J. Ha and I. Kubo. (2007) J. Agric. Food Chem. 55, 446-451.

Anisaldehyde, a potent melanogenesis potenciator. [T. Nitoda, M. D. Fan and I. Kubo. (2007) Z. Naturforsch. C: J. Biosci. 62, 143-149].

Molecular design of anti-MRSA agents based on the anacardic acid scaffold. [I. R. Green, F. E. Tocoli, S. H. Lee, K. Nihei and I. Kubo. (2007) Bioorg. Med. Chem. 15, 6236-6241.

Effects of cuminaldehyde on melanoma cells. [T. Nitoda, M. D. Fan and I. Kubo. (2008) Phytother. Res. 22, 809-813].

Design and evaluation of anacardic acid derivatives as anti-cavity agents. [I. R. Green, F. E. Tocoli, S. H. Lee, K. Nihei and I. Kubo. (2008) J. Eur. Med. Chem. 43, 1315-1320].

Effects of phenolic compounds isolated from Rabdosia japonica on B16-F10 melanoma cells. [T. Nitoda, T. Isobe and I. Kubo. (2008)] Phytother. Res. 22, 867-872].

Antifungal activity of alkanols against Zygosaccharomyces bailii and their effects on plasma membrane. [K. Fujita, T. Fujita and I. Kubo. (2008) Phytother. Res. 22, 1349-1355].

Sweet and bitter constituents of Wilbrandia species. [M. Ochi, K. Moriyama, K. Ohmae, Y. Fukuyama, K. Nihei and I. Kubo. (2009) Food Chem. 115, 61-65].

Recent Teaching

  • 119 - Chemical Ecology
  • 193 - Introduction to Research in Toxicology
  • 199 - Supervised Independent Study and Research
  • 299 - Nutritional Sciences and Toxicology Research

Contact Information


Office: 232A Hilgard Hall

Office Phone: 510-643-6303

Fax: 510-643-5438

Office Hours

Thursday 1:30-4:30, By Appointment, Updated: 2010/08/20

Research Group(s)

Mailing Address

Dept of Environmental Science, Policy, & Management
UC Berkeley
130 Mulford Hall #3114
Berkeley, CA 94720