Tumbuhan merupakan sumber yang kaya dari senyawa-senyawa bioaktif. Senyawa bioaktif yang berasal dari tanaman dapat digunakan sebagai obat atau prekursor dari obat semisintetis, dan dapat memberikan masukan berharga untuk pengembangan desain produk obat. Oleh karena itu ekstrak tanaman telah digunakan dan masih digunakan untuk mencegah dan mengobati beberapa jenis penyakit meskipun mekanisme aksinya terkadang belum diketahui. Akhirnya, terdapat permintaan global utuk proses produksi yang lebih “hijau”, yang lebih ekonomis, dan tersedia dalam waktu yang lama (Hendrawati et al. 2012).

Di seluruh dunia, lebih dari 50.000 sepesies tumbuhan digunakan untuk keperluan medis (Gómez et al. 2007). World Health Organization (WHO) hmemperkirakan bahwa lebih dari 80% dari populasi negara yang kurang berkembang di dunia bergantung pada pengobatan herbal untuk keperluan dasar kesehatan (Vines, 2004). Pasar obat herbal saat ini telah mencapai level US$62 miliar, diperkirakan akan bertumbuh hingga US$5 triliun pada 2050 (Joshi et al. 2004). Pasar dunia untuk obat herbal menunjukkan pertumbuhan tahunan yaitu 5– 15% (Kumar et al. 2008). Di Inggris Raya, lebih dari 25% populasi menggunakan obat-obatan herbal pada keperluan sehari-hari (Vines, 2004).

Pada 30 tahun terakhir, lebih dari 25% dari obat-obatan baru disetujui yang berasal dari tanaman dan sepertiganya yaitu sekitar 980 produk farmasi baru dihasilkan atau terinsipirasi dari produk alami (Newman et al., 2007; dan Terryn et al., 2006). Sekitar 50% dari penjualan bahan kimia tertinggi adalah berasal dari pengetahuan metabolik sekunder tumbuhan (Terryn et al., 2006). Sekitar 40% dari produk farmasi di Amerika Serikat dan Eropa menggunakan tanaman sebagai sumber bahan mentah (Ganapathy, 2006).

Selain tanaman dan ekstrak tanaman, senyawa murni yang dihasilkan dari tanaman memainkan peranan penting dalam pengobatan dan farmasi kontemporer. Senyawa khas tanaman yang biasa digunakan adalah terpenoid, alkaloid, polyketide, phenylpropanoid, dan flavonoid. Sebagai contoh, struktur disajikan dalam gambar 1, morphine dan codeine dari Papaver somniferum L., artemisinin dari Artemisia annua L., paclitaxel dari Taxus brevifolia Nutt, genistein dari Glycine max L. (Merr.), scopolamine dari Dubosia species, campothecin dari Camptotheca acuminata Decne, dan podophyllotoxin dari Podophyllum species (Hendrawati et al. 2012).

Gambar 1. Struktur kimia dari beberapa senyawa turunan yang penting dalam farmasi.

Sebagian besar metabolit sekunder diturunkan dari jalur shikimate, terpenoid, dan polyketide (Gambar 2). Jalur shikimate adalah sumber penting dari phenylpropanoid dan senyawa aromatis (Bentley et al., 1990; dan Hermann et al., 1999), seperti flavonoid, coumarin, isoquinoline dan indole alkaloid, lignan, lignin, dan anthocyanin.

Jalur terpenoid menyediakan sepertiga dari semua metabolit sekunder yang diketahui, meliputi mono-, sesqui-, di-, tri-, dan tetraterpene. Jalur ini juga merupakan sumber dari C5 pada isoprene pada beberapa skeleton dari beberapa sumber biosintetik, seperti anthraquinone, naphthoquinone, cannabinoid, furanocoumarine, dan terpenoid indole alkaloid (Veerporte, 2000).

Jalur polyketide merupakan sumber yang kaya akan senyawa bioaktif seperti anthranoids. Jalur ini menarik sebagai model studi rekayasa metabolik karena struktur kompleks yang dihasilkan dari unit C2 sederhana yang dikombinasikan pada jalur lain dan pengaturan konstruksi dari katalis ensimatis yang dapat mengontrol struktur enzim (Koffas et al. 1999).

Gambar 2. Jalur biosintetik yang telah disederhanakan dari metabolisme primer dan sekunder pada tanaman (Kumar et al. 2008).

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