How Can I Put Meta_Compare in the Database-Query? [Wordpress]

Question

or something like > current date

<?php
$currentdate = date("Y-m-d G:i:s", $timestamp);

$querystr = "
SELECT * FROM $wpdb->posts
LEFT JOIN $wpdb->postmeta AS term ON(
$wpdb->posts.ID = term.post_id
AND term.meta_key = 'vst_ort'
)
LEFT JOIN $wpdb->postmeta AS course ON(
$wpdb->posts.ID = course.post_id
AND course.meta_key = 'vst_date'
)
WHERE $wpdb->posts.post_status = 'publish'
AND term.meta_value = '$value3'
ORDER BY course.meta_value ASC
    ";
     $pageposts = $wpdb->get_results($querystr, OBJECT);
?>

thank you!